Are LDR pres the ultimate passive? [Archive]

Figlet108

26-05-2014, 15:39

Yesterday I was over at Macca's gaff where we had ourselves a mini passive pre bake-off.

Both of us seem to be attracted to the concept of how LDRs work and certainly on paper from an objectivist perspective they should sound very transparent and uncoloured. We had both bought a cheap Stereo Coffee single input LDR pre kit (http://www.ebay.com.au/itm/Light-Dependant-Resistor-Single-input-Preamp-Kit-/291041024249?pt=AU_Electronics_Audio_Amplifiers&hash=item43c36598f9) (~£50) about 8 months ago! and it was high time to try them out and see if Objectivist theory and Subjectivist reality would converge...

I made mine into a 2cm thick limestone box:

https://lh4.googleusercontent.com/-CtmUlRzQ_pM/U4NWDAY3IGI/AAAAAAAAC7w/VLJWNJi8KDE/w849-h566-no/2014-05-26+14.42.39_resize.jpg

Meanwhile I'd also bought a Tortuga LDR3x.V2 kit (http://www.tortugaaudio.com/product/ldr3x-passive-preamp-controller-version-2/) (~£250) with dual LCD displays and manual and remote control.

Not made the case for this yet, so here it is languishing naked next to the 12v power supply I made for it:

https://lh3.googleusercontent.com/-WoeEibW-Sd8/U4NXoHd22NI/AAAAAAAAC78/geoGECRT2NI/w849-h566-no/2014-05-26+14.28.37_resize.jpg

Macca has an NVA P90SA pre (£640) which uses these Shinkoh/Elms 24 stepped attenuators (http://www.hificollective.co.uk/catalog/glasshouse-shinkohelma-stepped-attenuator-mono-p-2179.html) and I can imagine it's as good a stepped attenuator passive as any out there and probably better than many. (I also used to have one of these for a couple of years before I moved it on and liked it).

We used the excellent Red Hot Chillies album 'Blood, Sugar, Sex, Magic' as music fodder and tried to level match as best as we could with the sound meter on my phone (not perfect but close enough).

It was clear pretty quickly that both LDRs were very close to each other and a step up on the stepped attenuator. The stepped attenuator was more fuzzy, less detailed, less transparent than both LDRs. The LDRs had better slam on the bass and more of a sparkle at the top end with cymbals and high-hats etc. We both remarked on the excellent reverb and decay.

In the end the LDRs were addictive to listen to and we didn't want to turn them off, in a way that the Stepped Attenuator wasn't.

While the 2 LDRs were very similar we both thought that maybe the Tortuga just had the edge by a whisker. The other thing about the Tortuga is the awesome engineering and attention to detail that's gone into it as a product. It's clearly a labour of love by a genuine hifi geek and it's the kind of thing I'd love to be doing if I had the skills.
The stand out features are that it has built in and automatic channel matching controlled by the embedded software. The Apple Remote control option and the dual LCD displays are icing on the cake. I also understand that in the near future it will be software update-able via it's built in USB interface and there will also be an android/iphone app to control it.

On the other hand, the Stereo Coffee LDR is wonderfully affordable at only £100 for 3 inputs and considering it sounds 95%-99% as good as the Tortuga it's also a very compelling proposition.

I needed 2 pres so I didn't have to choose between them, but if I had to rank them on their overall package of sound and features it would be thus:
1. Tortuga LDR3x.V2 (~£250 for 3 inputs and with all the options: manual and remote control, dual LCD displays)
2. Stereo Coffee LDR (£85 for 3 input version)
3. NVA PS90SA (£640 with 6 inputs)

To make sure these comments are put in the right perspective, all 3 pres were excellent and it wasn't night and day between any of them. The comments are relative to 3 very good passive pre amps.

I'm looking forward to some long term listening with the 2 LDRs and will post more comments, but I'm now wondering if LDRs have matured to the point that make them the ultimate passive pre?

Sovereign

26-05-2014, 15:56

Great read, thanks

kenworthy100

26-05-2014, 16:01

Fascinating stuff, very tempted to try one of these in my office system.

Figlet108

26-05-2014, 16:05

It'll be well worth it John, and both are super easy to connect up - no compulsory soldering involved.

It's also worth mentioning that Tortuga also have fully made up products as well as DIY kits, and that Stereo Coffee are also planning a fully made up product in the future. Obviously these are more expensive, but sometimes not having to do DIY is worth the extra money...

Puffin

26-05-2014, 16:13

Macca

26-05-2014, 16:24

It was very hard to tell the difference between the Stereo Coffee and the Tortuga. If we had more time to swap them in or out we probably could have worked it out but it was very close. I do wonder if the differences between the two LDRs and the NVA stepped attenuator might not have been down to the LDRs being a better match for the power amp, especially as for me the main difference was in the bass, with the LDRs offering just a little more of everything, slam, drive and tone. When we hooked up the Coffee pre to a different power amp from my usual XTZ I though the bass performance deteriorated noticeably.

Of course there is no such thing a free lunch and we have yet to see how these pre amps fair up to daily use over a period of time and if they will exhibit any of issues that have previously hampered this technology from delivering consistently.

Marco

26-05-2014, 16:53

Macca

26-05-2014, 17:53

Marco

26-05-2014, 17:58

We defo should... I could probably get to your gaff in less than an hour! :)

Or you could bring your passive up here... I don't believe you drive, Martin? However, I bet that you could get a train straight to Chester station, where I could pick you up.

Marco.

Macca

26-05-2014, 18:01

Yep when I've got the LDR passive up and running and I'll bring both.

Marco

26-05-2014, 18:09

Sounds like a plan, so let me know! :)

Marco.

Barry

26-05-2014, 18:09

Great write up Jason!

I've always been interested in the idea of LDR controls, if only for their elegance and simplicity. Yet I had niggling doubts concerning the linearity of the LED/LDR devices themselves. Following you review/appraisal it would seem that LDR attenuators do have advantages over a simple resistor stepped attenuator.

What would be nice would be a 'bake off' between the LDR device and a stepped transformer attenuator.

Figlet108

26-05-2014, 19:07

I made several LDR pre-amps both for myself and others following the disclosure by Mr Stanscheff of his circuit. There was a long thread on Diyaudio about 3-4 years ago. The one that I use in my system now is the first one I built on a piece of perfboard and cost about £15 including a simple 7805 circuit to power it. I was amazed by the sound then and I still am. I later added a motorised Alps pot as I had a remote board and controller from a previous project. IMO it has a lot of the quality's of a good active pre. I am also amazed that it is still working perfectly (tempting fate here!)

Rob, it's interesting that you have had your LDR for a while and that you still really rate it. The test of time is obviously not something I have experience of yet.
It's also interesting that unlike other pres, you can be confident that adding something like a remote motorised volume control can't (in theroy) effect the signal path in any way, so it's a guiltless option :)

Figlet108

26-05-2014, 19:14

Pity there wasn't a good valve preamp in there to add another interesting and valid facet to the test... If you guys had said you were doing this, I'd have popped down and brought the Croft! ;)

Marco.

Marco, actually Martin and I were thinking about having a listening session over at mine when he comes to collect his Stereo Coffee LDR once I connect it up. Why don't you join us and we can all have a listen to your Croft, the NVA and one or both of the LDRs?

Figlet108

26-05-2014, 19:22

Great write up Jason!

I've always been interested in the idea of LDR controls, if only for theor elegance and simplicity. Yet I had niggling doubts concerning the linearity of the LED/LDR devices themselves. Following you review/appraisal it would seem that LDR attenuators do have advantages over a simple resistor stepped attenuator.

What would be nice would be a 'bake off' between the LDR device and a stepped transformer attenuator.

Barry, what I would have liked to happen was for this mass bake off that Macca was trying to organise to go ahead, and for folks to bring their passive pres so that there would be representation from all different types of passives, including transformer based ones.

I know I only have one data point so far, but I suspect that LDRs in general will be better in general as a technology compared to resistor stepped attenuators. I don't think there is anything wrong with the NVA we used, I think it's more the technology that has its limits.
So yes, I'd be interested in taking the next step and comparing with stepped transformer attenuators.

Who has a good one and can we arrange a bake off?

Marco

26-05-2014, 19:33

Marco, actually Martin and I were thinking about having a listening session over at mine when he comes to collect his Stereo Coffee LDR once I connect it up. Why don't you join us and we can all have a listen to your Croft, the NVA and one or both of the LDRs?

I'm well up for that - just let us know when you fancy it! :cool:

Marco.

jandl100

26-05-2014, 19:40

I had a DIY Paradise Eva2 LDR passive pre for quite a while, and yes it was excellent in its way - transparent and well detailed. But it didn't have the drive of a decent active pre, imho, it sounded a just a little bit limp in the systems I used it in. Not a very 'exciting' listen. I kept it as a spare for quite a while, but never really felt the need to reinstate it so sold it on.

One of these ....

http://i9.photobucket.com/albums/a52/jasnev/ebay%20hifi%20sale/Eva21.jpg

Figlet108

26-05-2014, 20:30

Absolutely Jerry, and I'm not at all suggesting passives are for everyone.
This isn't really an active vs passive thread.

But for those like me that are firmly determined to build systems around passives, I'd like to find out if any of the passive technologies are generally and fundamentally better than all the others. Or are passives technology-agnostic and it's just down to the individual products?

Figlet108

26-05-2014, 20:39

I'm well up for that - just let us know when you fancy it! :cool:

Marco.

Yep, I'll PM you both.

Marco

26-05-2014, 20:55

Coolio on the forthcoming sesh :) I'm curious about this statement, though:

But for those like me that are firmly determined to build systems around passives...

Why? For me, that kind of thinking is way too restrictive.

I'd never be "firmly determined to build a system" around ANY specific component, as by doing so I might be missing out on using something else that's better...!

Therefore, my system building methodology has always been to keep an open mind, dismiss nothing out of hand, listen to as much different kit as possible, and be prepared to update my opinion, as to what is considered as 'best', at any time!! ;)

Marco.

Figlet108

26-05-2014, 21:28

I actually agree with you Marco. It's just where I am right now in my hifi journey. I just want to focus on passives for now, but I didn't say it would be that way forever.

Marco

26-05-2014, 21:29

Sure, that's fair enough :)

Marco.

CornishPasty

26-05-2014, 23:13

Light Dependant Resistor

26-05-2014, 23:46

Figlet108

27-05-2014, 00:27

What it is about a passive that floats your boat Figlet?

I have a Django TVC which I use occasionally, currently configured to +6dB but can easily be reset to 0dB and a B4 buffer stage which whilst it's powered is unity gain. It's a very interesting listen. However I've pretty much returned to my Grounded Grid valve preamp in my main system for the same reason Jandl gave.

Hi Ralph, the thing is that in my system the negatives that Jerry describes about his former LDR, (the same criticisms that I've heard in general about passives), I just don't experience. I get the transparency and detail but with plenty of drive, lots of excitement and not at all limp (so I guess er... stiff :) )

The Young DAC I use sends a strong signal and has a low impedance, the EAR509s have a relatively high impedance and my speakers have super simple cross-overs that are really easy to drive. Passives just work really well in that setup.

On the other hand if Marco's Croft blows me away it will certainly change my perspective.

Figlet108

27-05-2014, 00:31

Hi Jason
Magnificent effort with all of the hifi hardware including building casework, and arranging a bake-off with more to come.

Would be interested to know if you used our earlier control board or the last one we sent you ? As usual updates are sent without cost to our customers, and some improvements are being researched.

Cheers / Chris

Hi Chris,

I used the latest control board you sent and the latest (500k) pot too.
And the PSU was back up to 12v as we discussed.
The only thing that I realise now I forgot to do was remove the ground connection from the control board. I think you said that would improve things slightly and I'll make sure I make that change.

Light Dependant Resistor

27-05-2014, 00:49

Hi Chris,

I used the latest control board you sent and the latest (500k) pot too.
And the PSU was back up to 12v as we discussed.
The only thing that I realise now I forgot to do was remove the ground connection from the control board. I think you said that would improve things slightly and I'll make sure I make that change.

Hi Jason
The latest control boards already break that connection to other circuitry. So you can try with or without. The effect with J2 Control board ground connected with the latest boards is to place in parallel with the DC output a small capacitor and resistor if you wish to use it.

Cheers / Chris

Marco

27-05-2014, 09:30

On the other hand if Marco's Croft blows me away it will certainly change my perspective.

As ever in life, it's a benchmark thing, and so ultimately a question of what one is used to. In that respect, sampling a glass of Cava may initially be wonderful, but only until one savours the delights of Dom Pérignon... ;)

Marco.

awkwardbydesign

27-05-2014, 12:35

Paul Hynes

27-05-2014, 12:46

Puffin

27-05-2014, 14:57

Rob, it's interesting that you have had your LDR for a while and that you still really rate it. The test of time is obviously not something I have experience of yet.
It's also interesting that unlike other pres, you can be confident that adding something like a remote motorised volume control can't (in theroy) effect the signal path in any way, so it's a guiltless option :)

I have a very good valve pre (current price £800) and I prefer the LDR pre:)

r100

27-05-2014, 15:01

thank's for the write-up guys.

Techno Commander

27-05-2014, 16:15

Yomanze

27-05-2014, 17:36

CornishPasty

27-05-2014, 21:46

Interesting Jason, thank you. I should have a listen to an LDR preamp at some point then. I have seen on a forum somewhere some guy in the States who uses an LDR volume control in place of the conventional pot in an active preamp. I never thought much about it at the time but the cogs have starting turning.

r100

28-05-2014, 19:54

Or how about "low-impedance shunt"?

http://www.audialonline.com/online-topics/introducing-the-model-a/

"Back in 2002 I followed the (main)stream that dictated the use of high impedance input amplifier, and that was why I settled on and experimented with input buffer. (The one I recommended was very good one though, dare I say.) Since those days I moved however practically entirely to quite capable sources, which can drive sub 1 kOhm impedances with no issues. Apart from putting an input buffer out of equation, this also made possible to design volume control at lower impedances, which appeared to improve potentiometer based volume control to previously unexpected level. Such a volume control clearly overcame any other option, whether it is based on a classic pot, resistive attenuator, TVC, LDR, or even digital potentiometer."

looks very interesting, .. do you own an Audial A1 amp or have any info about its sound ?

Yomanze

29-05-2014, 11:30

No, but I want to try one. If his DAC is anything to go by it will be dead neutral and grain free with no false character, just gets out of the way allowing the "musicality" to shine through.

r100

29-05-2014, 16:17

i like the fact that the manufacturer/ designer sells directly to his clients. The hardware certainly looks pro. Would love to hear from you when you get one ;-)

Figlet108

30-05-2014, 14:22

This is interesting. I have been following Jason's limestone box build over at the other place, as I am using the same stone on my speakers. Then I get a PM from Chris mentioning this pre (I used to buy opamps from him). And I use a Promitheus TVC! Sadly Plymouth is a bit far to pop over for a bake off, but I will be back in Manchester next month visiting friends, so maybe something could be arranged. Hopefully someone else will turn up with a comparable TVC so I can see how it compares with the LDR.
I don't know what it would cost to make the LDR pre, but it is something that might interest me.

Hi Richard, very interesting. If the Manchester trip yields any opportunity that would great. You are of course welcome to pop over to Macc with your TVC if time permits.
In terms of costs, I think you can build a single input Stereo coffee LDR without a case for about £50.
OTOH, I believe Chris Daly is planning to circulate a fully made up demo LDR amongst the AOS members for trial.

P.S the 'other place' Richard refers to is the Wam, not the lair of Voldermort and his Death Eaters...

Figlet108

30-05-2014, 14:28

I first tried using LDRs for volume control around 20 years ago and was immediately impressed with their musical attributes compared to any other volume control I had used. Still using them, and still not found anything better for use in my system.

For those new to LDR volume control there is a very long thread on DIY Audio Forum covering the ins and outs of using them at :-

http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html

Paul

Hi Paul, that's a pretty strong endorsement.
I assume then that you haven't suffered any channel imbalance or any other issues that some nay-sayers like to bray about?

Yes I've dipped into that 'thread' - it's 5213 posts long! And spans 8 years from 2006-2014. So I'm guessing there must be something valid about LDRs as a pre technology.

Figlet108

30-05-2014, 14:30

I have a very good valve pre (current price £800) and I prefer the LDR pre:)

Care to share what that valve pre is?

Figlet108

30-05-2014, 14:35

I always thought this (http://www.akustyk.com/stereo_selector.html) little beasty from Poland looked pretty good for a reasonably cheap passive.

http://www.akustyk.com/stereo_selector/1.jpg

With the Yamamoto (http://www.ebay.co.uk/itm/Yamamoto-Sound-Craft-High-end-Attenuator-AT-03-3A-/201001669130?pt=UK_AudioTVElectronics_HomeAudioHiF i_Amplifiers&hash=item2ecca2120a) at the scary end of the scale.

http://www.phileweb.com/news/photo/201006/yamaa_big.jpg

Yep, those are definitely up there with the best of the stepped attenuators from what I have understood.
The KHOZMO was baked off with the Tortuga (I forget where I read it) and the Tortuga came out top. But I'd certainly like to hear a KHOZMO for myself and compare them. They do look very appealing.

Ali Tait

30-05-2014, 14:36

Jazon, you get the PM?

Figlet108

30-05-2014, 14:41

Or how about "low-impedance shunt"?

http://www.audialonline.com/online-topics/introducing-the-model-a/

"Back in 2002 I followed the (main)stream that dictated the use of high impedance input amplifier, and that was why I settled on and experimented with input buffer. (The one I recommended was very good one though, dare I say.) Since those days I moved however practically entirely to quite capable sources, which can drive sub 1 kOhm impedances with no issues. Apart from putting an input buffer out of equation, this also made possible to design volume control at lower impedances, which appeared to improve potentiometer based volume control to previously unexpected level. Such a volume control clearly overcame any other option, whether it is based on a classic pot, resistive attenuator, TVC, LDR, or even digital potentiometer."

Hi Neil, very interesting. I must confess to have a very strong hankering to try Pedja Rogic's products, especially the DAC. I've definitely got DAC-envy for your Audial Model S!

I must admit I don't really know what a low-impedance shunt is in the context of a pre amp? That product you link to is an integrated isn't it. I suppose Pedja has no plans to produce a stand-alone passive pre... which is a shame.

Figlet108

30-05-2014, 14:42

Jazon, you get the PM?

No, didn't see it - I'll have a look now...

Puffin

30-05-2014, 19:21

Care to share what that valve pre is?

http://i73.photobucket.com/albums/i239/saxonsex/MC7-R_zps07965a36.png

http://www.mingda.co.uk/mc7r.html

Stratmangler

08-06-2014, 12:31

It was good to see you yesterday Jason.
I liked what you've done with the LDR volume control - the limestone box is a nice way of housing everything, and more important than that, the LDR attenuator doesn't seem to manipulate or suck out the tone from any signal passing through it.
I'm very definitely thinking of pursuing the idea further.

https://lh4.googleusercontent.com/-CtmUlRzQ_pM/U4NWDAY3IGI/AAAAAAAAC7w/VLJWNJi8KDE/w849-h566-no/2014-05-26+14.42.39_resize.jpg

The guitar setup and repair place I mentioned is here http://theguitarrepairworkshop.com/

Figlet108

09-06-2014, 18:19

Likewise Chris, a very enjoyable day all round.

Yes, the LDRs impress me more and more as time goes on - I'm listening to it now through my ESLs and the detail and unveiled clarity just puts a smile on my face :)

It was interesting to compare it yesterday to the Music First TVC passive pre (http://www.mfaudio.co.uk/classic.htm). I don't know which version it was, but those babies are £2000+ and are apparently 'the best pre amp ever made' :)
I don't think I'm speaking out of turn if I say that the general consensus was that the LDR was clearly better and 40x cheaper :)

Thanks for the guitar repair place link - I'll respond to that in Gary's guitar thread so we don't pollute this one.

Yomanze

09-06-2014, 19:32

Hi Neil, very interesting. I must confess to have a very strong hankering to try Pedja Rogic's products, especially the DAC. I've definitely got DAC-envy for your Audial Model S!

I must admit I don't really know what a low-impedance shunt is in the context of a pre amp? That product you link to is an integrated isn't it. I suppose Pedja has no plans to produce a stand-alone passive pre... which is a shame.

It'd mean trying a pot in a passive pre build with a much lower impedance than the usual 10k, 20k or 50k with a log law faking resistor. This is dependent on the source being able to take such a low impedance, which the Model S does.

Spur07

14-06-2014, 19:58

Puffin (Rob) first introduced me to the LDR pre by loaning me one of his builds and I was amazed at the quality. I later went on to make my own build. I still prefer my active pre with my Quad II's though. A passive wont suit every system.

Figlet108

14-06-2014, 20:35

Agreed Paul. Rarely is any one thing the right thing for everyone, and those who love what actives do won't be swayed by any passive and vice versa as each technology has general pros and cons that attract different affinities.

At least though you have tried both and are able to make an informed decision. I on the other hand have never tried an active pre in my home, which is why I avoid the active vs passive debate. So I'm looking forward to hearing Marco's active Croft in my system and experience the character of an active for myself.

awkwardbydesign

15-06-2014, 09:55

I on the other hand have never tried an active pre in my home,
Now that strikes me as being unusual!

Figlet108

15-06-2014, 10:09

Yes, it is unusual I agree.

But you see for many years I was an NVA fanboy and subject to their brainwashing, so actives were never on the agenda. When I escaped and embraced the wider world and bought the EAR509s I now use, I was happy just plugging the DAC directly into them (I only have 1 source) and setting the adjustable levels built into the 509s. I then attenuated in the digital domain in software.
Then when I decided digital attenuation was compromising the sound and I wanted a pre between the DAC and 509s, it just coincided with me reading about LDRs, and Stereo Coffee popped up here on AOS promoting their stuff.

So to cut a long story short, my particular HiFi journey just hasn't included any active pres...

DSJR

15-06-2014, 11:08

Jason, this from me as well, but I don't think the NVA way of doing it (passive preamp) is 'brainwashing' as you say (maybe you're looking at other things which are not the subject of my reply). The gain (and input impedance?) of an NVA amp isn't so far off a vintage Quad 303/405, so it could be argued perhaps, that the 'active line buffer' is actually in the power amp, making an active preamp stage redundant and totally unnecessary? Many ss amps from the bad old days were basically power amps with a volume control and input selection before them - Cyrus 1 and 2 come clearly to mind). My geriatric Amcron/Crown amps were thought to be low gain products, yet I find I have to use the gain controls on the front to reduce the levels when used even with their own preamp (the reasons for this were well documented, so no foo here, and this was ten or more years before CD came along).

It's been suggested elsewhere that there are genuine reasons why LDR products such as preamps aren't available in the UK. I have not done any research on this, but please be careful when making these things up and disposing of any bad bits that may occur in assembly.

Figlet108

15-06-2014, 12:15

Hi Dave, my brainwashing comment was a general one and used to highlight why my hifi experience has been somewhat sheltered. I'm sure you're right about different power amps being designed with passives in mind.
Anyway, I'm not in that situation now so I can play with passive and active pres to my hearts content and make my own informed decision.

Incidentally, back in the day I plugged a number of (active) DACS directly into NVA amps and I never had any problems, and other than the digital attenuation limitations, they sounded pretty good to me.

Also, I AM NOT MAKING LDR circuits - that's back to the brainwashing 'elsewhere'. The Stereo Coffee and Tortuga DIY kits are already made up. You just plug the modules together. I have never handled an LDR in my life and don't intend to. I'm happy to pay Chris and Morten for my LDR needs :)

As for the LDR component not being RoHS compliant - I couldn't care less, as I'm sure is the case with most people. I'm never going to handle them. There are many many things that are not RoHS compliant and much more dangerous than a few LDRs in an enclosed box. And let's face it, the reasons this FUD is being spread elsewhere is for personal, political and business agenda reasons - so let's not pretend otherwise :)

Macca

15-06-2014, 12:36

Firebottle

15-06-2014, 12:57

Fair play to Martin on this call. I'm guessing it is the same situation as with large power transistors, particularly ones designed for radio frequency applications.
They come with a warning that they contain Beryllium oxide, which is highly toxic. Providing you don't damage them physically or cut them open they are perfectly safe, but dud ones do need to be disposed of properly.

Cheers, Alan

NRG

15-06-2014, 13:32

Putting on my moderator's hat for a second: Re CE compliance and potential health and safety issues I would appreciate it if Chris and Morten and anyone else with knowledge in this area were to give their opinions on this subject.

If this is reference to the LDR component its self then this should shed some light(!) :D ;)

http://www.electronicsweekly.com/directive-decoder/exemptions/2-new-additions-to-the-rohs-ex-2011-09/

awkwardbydesign

15-06-2014, 14:01

If this is reference to the LDR component its self then this should shed some light(!) :D ;)

http://www.electronicsweekly.com/directive-decoder/exemptions/2-new-additions-to-the-rohs-ex-2011-09/
40…Cadmium in photo resisters for analogue optocouplers applied in professional audio equipment. - See more at: http://www.electronicsweekly.com/directive-decoder/exemptions/2-new-additions-to-the-rohs-ex-2011-09/#sthash.rBPa00I6.dpuf

NRG

15-06-2014, 14:57

40…Cadmium in photo resisters for analogue optocouplers applied in professional audio equipment. - See more at: http://www.electronicsweekly.com/directive-decoder/exemptions/2-new-additions-to-the-rohs-ex-2011-09/#sthash.rBPa00I6.dpuf

That links to the same article, while its debatable what constitutes 'professional Audio Equipment' my point was the exemption expired at the end of last year. http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2012:348:0018:0019:EN:PDF

The above PDF says the research for cadmium free technology is in progress and substitutes could become available by the end of 2013. Does anybody know if a Cadmium free replacement has been developed yet? or if an extension for the exemption has been submitted?

Figlet108

15-06-2014, 16:11

No, there doesn't seem to have been any progress on this as far as I can see - read here (http://www.electronicsweekly.com/directive-decoder/rohs2/happened-exemption-light-dependant-resistors-2014-02/).

"...This expired on 31 December 2013 so it can be no longer be used and there is no replacement exemption. There are no drop-in replacements available."

Like I said before though - the origin of this focus on RoHS compliance is a smokescreen masking personal and professional prejudices.
If you are going to genuinely worry about the 'health' implications of owning an LDR pre, you had also better remove the mercury from your fillings, never smoke or drink and never walk out in the street and breath in car fumes, don't put a mobile to your ear, don't eat processed or fatty foods etc etc etc...

So let's just get this into perspective and not get side-tracked via remote-control prejudice :)

awkwardbydesign

15-06-2014, 16:18

And the exemptions to lead free solder tend to make a nonsense of that aspect too. Especially when you think of the amount of lead in one car battery!

Figlet108

15-06-2014, 16:22

Excellent point Richard. Those that are spreading this FUD solder with fully leaded solder almost every day!

Also better ditch all those solar panels:

"Cadmium in Solar panels - Cadmium telluride (CdTe) thin-film PV modules in photovoltaic panels are explicitly allowed by RoHS to contain unlimited cadmium, even though cadmium is restricted in all other electronics. The solar panel exemption was in the original 2003 RoHS regulation and it was further extended on May 27, 2011" (Wiki)

Firebottle

15-06-2014, 16:24

Let's face it, unless you are going to break open the LDR or ingest it :doh: you are in no danger at all.

It is all down to the regulations on hazardous substances leading to no one wanting to deal with waste containing Cadmium. You'll just have to keep the LDR pre for ever:rolleyes:

Alan

Marco

15-06-2014, 16:37

Like I said before though - the origin of this focus on RoHS compliance is a smokescreen masking personal and professional prejudices.

<Snip>

So let's just get this into perspective and not get side-tracked via remote-control prejudice :)

Spot on, Jason.

The creator of said smokescreen tried the very same thing during the recent studio cable/RCA plug tests here [create doubt about their efficacy, in order to protect his own commercial cable-selling interests], which rightly fell on deaf ears, just as should happen with this latest scaremongering nonsense about LDRs (due to smokescreen-boy's fear that their increasing popularity will affect sales of his passive preamps), which doesn't apply to ordinary end-users of LDRs, who will of course not be fiddling with the internals of the products concerned.

Further to that, as a manufacturer of solid-state amplifiers, he then tried to portray all valve amps as being some kind of illegal and 'inherently unstable incendiary devices', for the same commercially biased reasons, although under the guise (the same as he's now doing with LDRs) of being 'concerned' for people's safety, the irony of which will not be lost on those who know this person's true character.

It is his standard modus operandi, so best just to ignore the bluster. Like a bad smell, it will eventually clear...! Remember, 'don't feed the energy monster' ;)

Marco.

Marco

15-06-2014, 16:38

Let's face it, unless you are going to break open the LDR or ingest it :doh: you are in no danger at all.

Quite :)

Marco.

Puffin

15-06-2014, 16:53

Marco

15-06-2014, 16:57

Yes, but unfortunately he's turned into a mutant.

Marco.

Light Dependant Resistor

15-06-2014, 20:58

Putting on my moderator's hat for a second: Re CE compliance and potential health and safety issues I would appreciate it if Chris and Morten and anyone else with knowledge in this area were to give their opinions on this subject.

Hi Martin
To expose yourself to harmful chemicals within an LDR, you would have to shatter the case, then scrape back the lens surface, and inhale the resistive element in a closed air environment. So LDR's as packaged represent no risk to end users.

The EU discussions where LDR's are to be given further exemption from ROHS sadly broke down with competitors ( stating their product contained no Cds ) to the professional devices we and Tortuga use, entering with no greater aim than advertising their own un- encapsulated product, subsequently found by ROHS to contain Cds . It was with good reason that major professional manufacturers remained silent.

The observations also about other far more harmful products in the marketplace such as lead acid batteries is quite true, ROHS basically do not have the resources to control their use. It is quite likely too that ROHS will provide further exemption for encapsulated LDR's ,for audio specific use as there is no present device that has their unique audio low distortion ability, a point previously raised by Marshall amplifiers. Also the LDR's we supply their production continues by Advanced Phototonix who continue to supply retailers such as Allied, Crest, RS, and Farnell, indicating the product meets compliance at this and many other levels

So there is no harm with the NSL32SR2S and NSL32SR3 devices, as we supply them. I hope Morten can add his comments.

Cheers / Chris

Macca

15-06-2014, 21:11

Chris

Many thanks for taking the time to comment. It is much appreciated.

NRG

15-06-2014, 21:44

NRG

15-06-2014, 21:54

Figlet108

16-06-2014, 00:06

No worries Neal, I respect your views on this but I'm a little unclear on the details of the law in the case of a consumer.
I understand that a company importing non RoHS products to sell or incorporate in it's products and sell is illegal. I'm not sure that applies to me as an individual consumer buying a non RoHS product for my personal use.
I've spent some time googling the subject this evening and all I can find is reference to the illegality of companies importing non RoHS products, not individual consumers.
So right now I'm not sure that I have broken the law. Maybe someone who understands this more clearly can comment?

If I genuinely have broken the law, then while it's not necessarily their responsibility, I would have hoped that Chris and Morten would have warned potential customers from certain countries that they would be breaking the law by purchasing their products.

Edit: and just to add Neal that my comments in previous posts were not in reference to any legal aspect as I never for a second believed I was breaking the law by buying these products. My comments were regarding the realistic health implications and putting them into context, so I wasn't trying to deflect anything.

Light Dependant Resistor

16-06-2014, 00:34

Hi
In matters such as this it proves best to seek clarification from the bodies involved, rather than relying on speculation. I am presently writing to bodies involved and will report those findings.

My present understanding is that both Tortuga and Stereo Coffee are providing DIY components, not finished products to end users, and it appears then there is no definition applying. It would appear definition would apply to products then if manufactured in UK as finished and sold, where everything encased would have to be ROHS compliant.

I have also taken the step of trying to clarify this with the EU as their ROHS directive is difficult for end users and industry to interpret, a copy is below.

These are great questions, and we look forward to clarifying for you, so as you are clear and we are clear as to supply, with what arguably is the best audio coupling component presently available.:)

Cheers / Chris

Dear Madam / Sir Case_ID: 0915122 / 1182429
I refer to the COMMISSION DELEGATED DIRECTIVE 2012/51/EU
From my knowledge of the audio use of optocouplers, there has been no substitute found, to replace their unique audio properties. The directive therefore is a grey area, in that although expired, there is no available substitute.

The sufficient grey area causing unknown advice to end users and industry..

Can the EU provide advice as to the ROHS directive applying to the continued use of cadmium in the specialist field audio use of optocouplers.

Point also needs to be made that definition difference be given to Light Dependant Resistors that are encapsulated with emphasis of EU protection of their continued use. Example being the NSL32SR2 series including the S designation and NSL32SR3 which are highly regarded for audio use vs those Light Dependant Resistors containing cadmium that are non encapsulated, which due to manufacture appear to make little effort to adequately house the hazardous chemicals used. It is perhaps the latter that has influenced expiry, without due reflection on those LDR's that are encapsulated.

Encapsulated LDR manufacturers noticebly those excellent for audio use, having already made considerable effort to protect end users prior to the ROHS directive. These differences need to be reflected in any redraft or consideration of legislation, and that there are currently no substitutes.

I look forward to your reply

Yours Faithfully

Chris Daly

Light Dependant Resistor

16-06-2014, 06:13

Further to my post regarding asking the relevant bodies in the UK, I will await and publish their reply.
I have written also today to http://www.rohs.bis.gov.uk/ as follows:
( Note to Moderator I edited my website address from the quote below, as such advertising material is already within the Trade area of AOS )

I am an exporter from New Zealand of audio attenuator kits that use encapsulated LDR devices with part numbers NSL32SR2s , These encapsulated plastic LDR's are quite different to open face LDR's Cadmium sulphide is used in each for the variable resistive element, and aids the encapsulated part its excellent audio ability .

The UK market for these DIY kits is individuals purchasing via ebay, and my website .....

The kits are then typically assembled and used by that individual, with assistance in DIY spirit given to others to assist them get their kit going. As such there is no ongoing manufacture involving on -selling

Could you let me know if this style of sale contravenes any current legislation concerning ROHS expired items in the UK, and if not current any review date planned.

I have concurrently written to the EU Case_ID: 0915122 / 1182429
asking them as to the current status of LDR's that have no available replacement part yet their ROHS exemption has expired.

I would be most grateful for your reply.

Regards Chris

Figlet108

16-06-2014, 06:52

Nice one Chris. Your efforts to clarify the situation are appreciated.

NRG

16-06-2014, 07:23

No worries Jason, +1 to the above. Clarification would be good!

awkwardbydesign

16-06-2014, 09:22

I guess I'd better order one before they destroy the world, then!

Marco

16-06-2014, 13:55

GH6us7DLaRk

;) :eyebrows:

As I said earlier to Jason, in response to the 'origin of this smokescreen', which I think is worth repeating, in order that reality (EU regulation queries aside) is separated from the demented bluster of a bloke with an obvious commercial agenda:

The creator of said smokescreen tried the very same thing during the recent studio cable/RCA plug tests here [create doubt about their efficacy, in order to protect his own commercial cable-selling interests], which rightly fell on deaf ears, just as should happen with this latest scaremongering nonsense about LDRs (due to smokescreen-boy's fear that their increasing popularity will affect sales of his passive preamps), which doesn't apply to ordinary end-users of LDRs, who will of course not be fiddling with the internals of the products concerned.

Further to that, as a manufacturer of solid-state amplifiers, he then tried to portray all valve amps as being some kind of illegal and 'inherently unstable incendiary devices', for the same commercially biased reasons, although under the guise (the same as he's now doing with LDRs) of being 'concerned' for people's safety, the irony of which will not be lost on those who know this person's true character.

Amongst the legitimate enquiries currently being carried out into CE and RoHS, in reference to LDRs, the results of which will be revealed in due course, I would ask that no-one forgets the *real* reasons above responsible for why this situation was highlighted in the first place!!

That said, rest assured that AoS will not be aiding the promotion of a product that contravenes UK law. Therefore, appropriate action will be taken once the results of Chris Daly's enquiries into that situation are available.

Marco.

TortugaRanger

16-06-2014, 13:59

Hi Martin
To expose yourself to harmful chemicals within an LDR, you would have to shatter the case, then scrape back the lens surface, and inhale the resistive element in a closed air environment. So LDR's as packaged represent no risk to end users.

The EU discussions where LDR's are to be given further exemption from ROHS sadly broke down with competitors ( stating their product contained no Cds ) to the professional devices we and Tortuga use, entering with no greater aim than advertising their own un- encapsulated product, subsequently found by ROHS to contain Cds . It was with good reason that major professional manufacturers remained silent.

The observations also about other far more harmful products in the marketplace such as lead acid batteries is quite true, ROHS basically do not have the resources to control their use. It is quite likely too that ROHS will provide further exemption for encapsulated LDR's ,for audio specific use as there is no present device that has their unique audio low distortion ability, a point previously raised by Marshall amplifiers. Also the LDR's we supply their production continues by Advanced Phototonix who continue to supply retailers such as Allied, Crest, RS, and Farnell, indicating the product meets compliance at this and many other levels

So there is no harm with the NSL32SR2S and NSL32SR3 devices, as we supply them. I hope Morten can add his comments.

Cheers / Chris

I concur with Chris's statement on the subject.

I looked into ROHS with respect to LDRs a while back and found ambiguous guidance at best. I contacted the LDR manufacturer (Silonex - now Advanced Photonix) and spoke directly with their General Manager at length on the subject. Basically, without an implicit (if not explicit) waiver for photoresistors in general, practically all of Europe would become a photoresistor free zone due to their CdS content. Yet they continue to ship an enormous quantity of CdS photoresistors to their UK/EU distributors, a small fraction of which include audio grade LDRs. The reason this is allowed is there is no viable alternative photoresistive material available yet.

In terms of actual risk, as Chris mentioned, you'd either have to burn your LDRs and breathe in the fumes or eat them. Even if you ate them, you'd have to chew them up fairly good before swallowing since they're hermetically encapsulated in a plastic package. And if we're really going to get serious about Cd then all those batteries have got to go as well. Not to mention cigarette smoke which is the actual real leading source of CdS exposure to the general population. By now I suspect Keith Richards probably qualifies as a human LDR. And how about all those thin-film solar panels made with CdS spread out all over the fields of Europe. As of the end of 2013, First Solar had over 4,000 megawatts of installed solar panel capacity in Europe with more on the way. That's roughly the equivalent of 4-8 nuclear power plants. Those solar panels are exempted because they're encapsulated between sheets of tempered glass. You'd have to crush them and burn them to release the CdS in such a way that it would pose a health risk. Not likely. And their practical benefits far outweigh some theoretical risk scenario.

The practical reality is the audio grade LDRs used in our audio products are harmless.

Regards,
Morten

Marco

16-06-2014, 14:08

:clap: :clap:

Nice one, Morten. However, I must congratulate you on this bit, which was priceless:

In terms of actual risk, as Chris mentioned, you'd either have to burn your LDRs and breathe in the fumes or eat them. Even if you ate them, you'd have to chew them up fairly good before swallowing since they're hermetically encapsulated in a plastic package. And if we're really going to get serious about Cd then all those batteries have got to go as well. Not to mention cigarette smoke which is the actual real leading source of CdS exposure to the general population. By now I suspect Keith Richards probably qualifies as a human LDR.

Major LOL! :D :D

Marco.

r100

16-06-2014, 15:51

By now I suspect Keith Richards probably qualifies as a human LDR

:stalks:

:lolsign:

I want one

NRG

16-06-2014, 16:21

I concur with Chris's statement on the subject.

I looked into ROHS with respect to LDRs a while back and found ambiguous guidance at best. I contacted the LDR manufacturer (Silonex - now Advanced Photonix) and spoke directly with their General Manager at length on the subject. Basically, without an implicit (if not explicit) waiver for photoresistors in general, practically all of Europe would become a photoresistor free zone due to their CdS content. Yet they continue to ship an enormous quantity of CdS photoresistors to their UK/EU distributors, a small fraction of which include audio grade LDRs. The reason this is allowed is there is no viable alternative photoresistive material available yet.

In terms of actual risk, as Chris mentioned, you'd either have to burn your LDRs and breathe in the fumes or eat them. Even if you ate them, you'd have to chew them up fairly good before swallowing since they're hermetically encapsulated in a plastic package. And if we're really going to get serious about Cd then all those batteries have got to go as well. Not to mention cigarette smoke which is the actual real leading source of CdS exposure to the general population. By now I suspect Keith Richards probably qualifies as a human LDR. And how about all those thin-film solar panels made with CdS spread out all over the fields of Europe. As of the end of 2013, First Solar had over 4,000 megawatts of installed solar panel capacity in Europe with more on the way. That's roughly the equivalent of 4-8 nuclear power plants. Those solar panels are exempted because they're encapsulated between sheets of tempered glass. You'd have to crush them and burn them to release the CdS in such a way that it would pose a health risk. Not likely. And their practical benefits far outweigh some theoretical risk scenario.

The practical reality is the audio grade LDRs used in our audio products are harmless.

Regards,
Morten

I think there's some misunderstanding. Firstly, the statement "its harmless" could not be further from the truth. RoHS exists for a reason, these components are not 'harmless', they contain Cadmium and are not RoHS certified. Yes, you may have to chew them, smash 'em up or over heat them with a 1KW Soldering iron to commit suicide but 'harmless' they are not. The RoHS Directive was brought into force because these types of components or similar where/are used extensively in many electronic appliances and present a long term environmentally hazard for everyone.

The argument of "Better not cross the road or you'll die" is really irrelevant…yes the world is a nasty dangerous place and you can be struck down and die at any point if you are unlucky. The likely hood of dying from using one of the LDR Pres is about as likely as me marrying the Duchess of Cambridge, there's more chance of my RoHS exempt Cadmium filled Solar Panels falling off our roof and crushing me! But thats not the point!

The reason Advanced Photonix can still ship to the EU is because RoHS does not cover individual components only appliances that depend on electric current or electromagnetic fields in order to work properly and that this operation is their primary function. Build the components into a working circuit board or appliance that only requires a battery or power supply to work and it all changes.

I gained first hand experience of the RoHS initiative back in 2006, the US based hardware manufacturing company I was with at the time couldn't get their heads around it at first and when the penny finally dropped had to make sweeping changes and spent a lot of $$$ and man hours complying with the directive.

Anyhow I'm waffling and starting to sound evangelical! So I'll butt out of the thread.

guy

16-06-2014, 21:02

I think that RoHS regulations only apply to electrical devices (please feel free to put me right on this).

However, the interest in LDR passives caused me to do a quick search for cadmium. The following, wikipedia entry,was one the first references I found:

"One of the major elements of the REACH regulation is the requirement to communicate information on chemicals up and down the supply chain. This ensures that manufacturers, importers and also their customers are aware of information relating to health and safety of the products supplied. For many retailers the obligation to provide information about substances in their products within 45 days of receipt of a request from a consumer is particularly challenging."

I know that it sounds like a bit of a palaver for such small (and encased) amount of cadmium, but it is a cumulative poison (rather like lead is, and look what has happened with solder :roll: )
(Years ago I used to work as an analytical chemist and well remember having to carry out emergency analysis of chemical samples which had been bought in from the docks at Harwich. Areas of the docks would be shut down until I had completed my analysis, as some importers had failed to provide correct labelling/documentation. So I have some experience of how the lack of correct documents for importation can cause significant problems)

Interesting to note:
"From 1 June 2011, the European Chemicals Agency must be notified of the presence of SVHCs in articles if the total quantity used is more than one tonne per year and the SVHC is present at more than 0.1% of the mass of the object".
Note the concentration :o and that the presence of hazardous chemical is enough, whether or not it is encased and would need to be scraped, chewed and eaten.

Seems to me that the situation is similar to that which applies to Yamaha NS100 speakers:
Beryllium cone tweeters! I certainly wouldn't want to clear up the mess after a house fire where a pair had been, potentially dangerous, but "flies in under the radar"?

Figlet108

16-06-2014, 21:38

Guy I'm not sure I understand your point.

If you are coming at this from a legal point of view, then there's not much to say until Chris gets an answer from his letters.

If it's from a safety point of view how is a house burning down with LDRs or NS100s any different from a house burning with solar panels or leaded solder?

guy

16-06-2014, 22:05

Hi,

Just that it seems to me that, despite what has been said elsewhere in this thread, there are regulations in effect in the EU and that as a minimum these kits should have hazchem documentation.

Also the earlier point about the device only containing a small amount of encapsulated cadmium doesn't seem to be a relevant point from the point of view of REACH.

You are of course correct that from the safety point of view, a house fire with solar panels or NS100's is pretty much equivalent, my point would be that consumers need to be made aware of the potential risks and protected by legislation.

Figlet108

16-06-2014, 22:27

Interestingly I just searched on a number of suppliers of solar panels and leaded solder, and not one of them had any information about health risks. And when my leaded solder arrived from RS there was nothing about the health risks.

Sorry Guy but I just can't help question your real motivations for posting here given your affiliations.

If I'm wrong then accept my apologies, but that's how it looks to me.

r100

16-06-2014, 22:40

if you are going to eat or smoke your kit then there you could be at risk. If you just use the kit as intended there is no risk at all. smokescreenman is on a solitary mission and the DQ will clarify it if you are still in doubt... hahaha LOL:cool:

Marco

17-06-2014, 10:25

smokescreenman is on a solitary mission and the DQ will clarify it if you are still in doubt... hahaha LOL:cool:

A hilarious 'comedy duo', no doubt, but for all the wrong reasons! :mental: ;)

Like I've said before, there exists a very blatant and obvious commercial agenda behind this scaremongering, in reference to LDRs, which should be crystal clear to anyone in possession of at least one functioning neurone, no matter how much it is being strenuously denied, and the motivation for it deflected elsewhere....

Marco.

Ali Tait

17-06-2014, 10:54

Well, all I can say is, sound wise, the LDR sounded very good at Owston, bettering a Music First pre. Not bad for a £50 board.

Marco

17-06-2014, 11:37

Indeed, Ali. I'll be testing one against my Croft preamp soon, the results of which will be posted here :)

Marco.

Ali Tait

17-06-2014, 12:00

You'll be surprised..

Marco

17-06-2014, 12:10

Yup, I'm fully expecting to be! :)

Marco.

DSJR

17-06-2014, 16:54

A hilarious 'comedy duo', no doubt, but for all the wrong reasons! :mental: ;)

Like I've said before, there exists a very blatant and obvious commercial agenda behind this scaremongering, in reference to LDRs, which should be crystal clear to anyone in possession of at least one functioning neurone, no matter how much it is being strenuously denied, and the motivation for it deflected elsewhere....

Marco.

I promise I'm not part of any 'comedy team' on this, only to very respectfully say that the intention elsewhere as I took it, was stated to inform and then let potential purchasers make up their own minds. Anyway, I reckon that most peeps here would be in for a Tisbury at under a ton, rather than a perspex special at double the price or more - and I say this with respect and absolutely NO agenda I assure you (I can't afford any of them anyway :)). I still have a Tisbury agenda on the back burner and shall try one at some point as long as prices are kept within bounds.

guy

17-06-2014, 20:39

Interestingly I just searched on a number of suppliers of solar panels and leaded solder, and not one of them had any information about health risks. And when my leaded solder arrived from RS there was nothing about the health risks.

Quite amazed that your search of a number of suppliers turned up no information about health risks.
I googled "solar panels cadmium" and one of the first was this:

Cadmium Telluride (CdTe) is a commonly used material in thin film solar modules. Cadmium is a heavy metal and extremely dangerous. Cadmium fumes may cause flu like symptoms and more severe respiratory problems. Cadmium dust is even more toxic, leading to respiratory, liver and kidney problems that can be fatal. Some compounds containing cadmium are thought to be carcinogenic.

http://www.energymatters.com.au/index.php?main_page=news_article&article_id=1469

and the HSE produce this document:

http://www.hse.gov.uk/pubns/guidance/wl17.pdf

Sorry Guy but I just can't help question your real motivations for posting here given your affiliations.

If I'm wrong then accept my apologies, but that's how it looks to me.

My motivations are based in an interest in Chemistry, a professional qualification in instrumental analysis (LRSC) and having worked as a safety officer with ICI while working at the plastics division research centre (PVC dept funnily enough, given my love of vinyl), I do take an interest in chemical safety.
I also have an interest in passive preamps (I happen to use an NVA P50), an interest in Physics (happen to be an advanced skills teacher of Physics), and a genuine interest in music reproduction. So naturally, When I saw this thread on LDR pre amps I looked up the toxicity of Cadmium.

There; I have been open, honest, decent and truthful in revealing my motivations.

Even a cursory view of your posts here, and elsewhere, reveal that you have a problem with one particular manufacturer. Are you capable of being equally open, honest, decent and truthful?

By the way, apology accepted.

Marco

17-06-2014, 22:15

I promise I'm not part of any 'comedy team' on this, only to very respectfully say that the intention elsewhere as I took it, was stated to inform and then let potential purchasers make up their own minds.

Yes, that's what he wants folk to think. However, the reality is as I have already outlined. Also, the clue to his real 'beef' with LDRs lies in this piece of text:

About 4 to 5 years ago when the LDR thing started from a company in Malaysia they attacked my passive pre with publicity about how much better a LDR was. So I investigated the product design thoroughly to see if it was better and I discovered that it is both illegal to sell them or import them to the EU, so the project was shelved.

Note how he doesn't state what the results of his investigations were, in terms of the LDRs sonic performance, in comparison with that of his passive pre...

Why not ask him that question, or rather more specifically, to put aside for a moment his mania about legalities, and instead explain exactly how he thought the LDR he tried sounded? Basically, if it had been 'legal', would he have used it??

He's deliberately missed that bit out, and one can only surmise why..........

Furthermore, the man is known to rather dramatically lose the plot with anyone who 'attacks' his products, so this current thing with LDRs is simply another one of his 'revenge missions', coupled with a fear that the current popularity of LDRs could affect sales of his passive preamps. Therefore, he's doing his level best to spoil that by covering up his agenda with a smokescreen about regulations and safety, and in the process acting rather hilariously as 'The Peoples Legal Champion'...

Quite simply, anyone who can't see that is having the wool pulled over their eyes!

Marco.

Marco

17-06-2014, 22:59

And of course anyone who states that they, I quote: "investigated the product design thoroughly" (note the significance of that last word) will subsequently have arrived at some sort of conclusions regarding the efficacy of that product, no matter if it's simply based on a technical assessment, or how much they wish to kid others on that they haven't tried it!

Ees a naughty wee fibber, me thinks... ;)

Marco.

Marco

18-06-2014, 08:57

Incidentally, a wee birdy tells me that 'Cadmium Boy' still uses leaded solder in his current production amps, which has been banned for use in new consumer product production since around 2003......

Pot > kettle > black, me thinks...!

Marco.

Gordon Steadman

18-06-2014, 09:17

We seem to had this conversation before.....it seems to me that some people are taking an unholy joy in hitting back in kind rather than turning the other cheek. I thought we were not supposed to acknowledge a certain person's existence on here!

I am aware that the temptation must be great but you would all do far better to carry on with your own lives and occupations than entering into pointless bun fights.

Having said that, I see no problem in quietly checking things like regulations without making a song and dance about it. Any manufacturer has to abide by the rules and should know if his product breaks any of them. The DIYer can kill himself in private.

Marco

18-06-2014, 09:37

We seem to had this conversation before.....it seems to me that some people are taking an unholy joy in hitting back in kind rather than turning the other cheek. I thought we were not supposed to acknowledge a certain person's existence on here!

Indeed, Gordon. I completely understand, and of course you are right. However, *sometimes* in life important things need challenging - and so regardless of anything else, challenged they will be!

Marco.

anubisgrau

18-06-2014, 10:25

Well, all I can say is, sound wise, the LDR sounded very good at Owston, bettering a Music First pre. Not bad for a £50 board.

was it buffered (and how) or not?

Ali Tait

18-06-2014, 10:39

No buffer, just the board I think, Jason can confirm. Was faster and tighter in the bass than the MF, and as good or better everywhere else, which makes it great VFM IMHO.

r100

18-06-2014, 22:29

some clarification from Morten concerning the use of LDR's in his products and the bizarre EU rules which seem to allow, even subsidize other products containing CdS

http://www.audiocircle.com/index.php?topic=126747.0

anubisgrau

18-06-2014, 22:43

No buffer, just the board I think, Jason can confirm. Was faster and tighter in the bass than the MF, and as good or better everywhere else, which makes it great VFM IMHO.

would be good to know what is the output impedance of this LDR pre and if not variable, how it was fixed.

Light Dependant Resistor

18-06-2014, 22:57

Hi
I am pleased to advise reply has been received from the EU, clearing photoresistors for analogue optocouplers as there are presently no substitutes:

Dear Mr Daly,

Thank you for your message.

The Commission Directive 2012/51/EU has enabled the use of cadmium in photoresistors for analogue optocouplers as an exemption from the ROHS directive. Therefore, indeed, the use of cadmium in photoresistors for analogue optocouplers is currently allowed as there are no other substitutes. We draw your attention in this context to the recitals of the Directive:
http://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1403091086794&uri=CELEX:32012L0051

This new delegated Directive is based on the Recast of the RoHS Directive which entered into force in January 2013. The information relating to the recast of this Directive with the comments submitted during the public consultation is available on the following website of the Directorate-General for the Environment:
http://ec.europa.eu/environment/waste/rohs_eee/index_en.htm

If you wish to voice your opinion on waste management issues and changes to the EU legislation, we invite you to consult the public consultations webpage on DG Environment:
http://ec.europa.eu/environment/consultations_en.htm

We hope you find this information useful. Please contact us again if you have other questions.

With kind regards,
EUROPE DIRECT Contact Centre
http://europa.eu - your shortcut to the EU!

TortugaRanger

18-06-2014, 23:03

would be good to know what is the output impedance of this LDR pre and if not variable, how it was fixed.

In the case of our most recent ldr3x.v2 board, the input impedance is mostly fixed while the output impedance is typical of a nominal 20k potentiometer which is not fixed. More info on this including a graphic can be found in the Product Documentation section of our website via this link: http://www.tortugaaudio.com/documentation/#document-23

Cheers,
Morten

r100

18-06-2014, 23:03

;-)

NRG

19-06-2014, 07:20

Hi
I am pleased to advise reply has been received from the EU, clearing photoresistors for analogue optocouplers as there are presently no substitutes:

[I]Dear Mr Daly,

Thank you for your message.

The Commission Directive 2012/51/EU has enabled the use of cadmium in photoresistors for analogue optocouplers as an exemption from the ROHS directive. Therefore, indeed, the use of cadmium in photoresistors for analogue optocouplers is currently allowed as there are no other substitutes. We draw your attention in this context to the recitals of the Directive:
http://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1403091086794&uri=CELEX:32012L0051

..................

Sorry I have to come back in here...Chris, you may want to go back and clarify this with them, the 2012/51/EU exemption expired on 31st December 2013, it is clearly noted in the document.

12687

You may also want to clarify with them what they mean by "...professional audio equipment..."

CageyH

19-06-2014, 07:46

So it's not cleared for sale in Europe then?
It's a shame as I want to try a pre/power combo to see what that does.

Light Dependant Resistor

19-06-2014, 07:51

Hi
We are currently awaiting clarification from the UK National Instruments Office, as to ongoing sales in the UK. We will advise you with their reply as soon as it is made available. We must in the interim period provide them the time and ability to assess this issue. :)

Cheers / Chris

Light Dependant Resistor

19-06-2014, 08:00

Sorry I have to come back in here...Chris, you may want to go back and clarify this with them, the 2012/51/EU exemption expired on 31st December 2013, it is clearly noted in the document.

12687

You may also want to clarify with them what they mean by "...professional audio equipment..."

Hi NRG
Morten and I have been discussing this too, and there are links on the post I provided that get to a document 29/01/14, as though exemption was allowed up until the next EU hearing which has then provided further exemption.
I will try and refine this with URL links as soon as I can for you.

Marco

19-06-2014, 08:02

After reading this: http://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1403091086794&uri=CELEX:32012L0051

I presume then that means that Cadmium in photoresistors, for analogue optocouplers applied in electrical and electronic/audio equipment, was allowed before 31st December 2013, and so any stocks of LDR-based audio equipment belonging from that period would not be liable under the current expiration of the exemption from the ROHS directive?

If that's the case, then the supplying of stock built during that period (and there probably is some currently still in circulation), is perfectly legal. In any case, how would you ascertain or prove whether any LDR-based audio equipment, currently being supplied by various manufacturers, was built before or after the expiration of the exemption from the ROHS directive?

You may also want to clarify with them what they mean by "...professional audio equipment..."

Indeed. I could be wrong, but I take that to mean more 'high-end audio equipment' (i.e. the specialist stuff we as enthusiasts use), not simply pro-audio gear.

Marco.

Marco

19-06-2014, 08:13

Morten and I have been discussing this too, and there are links on the post I provided that get to a document 29/01/14, as though exemption was allowed up until the next EU hearing which has then provided further exemption.
I will try and refine this with URL links as soon as I can for you.

Hi Chris,

That's kind of what I understood from this bit, contained in the directive:

"However, that exemption should be limited in time as the research for cadmium free technology is in progress and substitutes could become available by the end of 2013."

Essentially then, the exemption would run until such times as said substitutes become available, which correct me if I'm wrong, don't yet exist? Therefore, the exemption would continue until such times as they do, meaning that LDRs are currently not prohibited for use in the EU.

However, if you could find any evidence to confirm the above, that would be great :)

Marco.

Figlet108

19-06-2014, 08:22

Marco, I reached the same conclusion as you in your previous post, that because no alternative has yet been found, the exemption still persists, which is how I understood the comment from the European Commission "...Therefore, indeed, the use of cadmium in photoresistors for analogue optocouplers is currently allowed as there are no other substitutes..."

That's a pretty clear and unambiguous statement, but I appreciate there is still some lingering ambiguity surrounding the wider context, so more clarification would be good.

NRG

19-06-2014, 08:38

Hi NRG
Morten and I have been discussing this too, and there are links on the post I provided that get to a document 29/01/14, as though exemption was allowed up until the next EU hearing which has then provided further exemption.
I will try and refine this with URL links as soon as I can for you.

That would be good as I can't locate the link your referred to...

NRG

19-06-2014, 08:54

Strange interpretation guys! Having been 'here' in the past when they say it 'expires on xx/xx/xx' they generally mean it 'expires on xx/xx/xx' ;)

The use of the term 'professional audio equipment' may be irrelevant now anyhow as I think RoHS 2 makes no distinction between EEE (Electrical and Electronic Equipment) for professional or consumer use.

Figlet108

19-06-2014, 09:04

was it buffered (and how) or not?

As Ali says, it's not buffered.
I think Morten addressed your question regarding the Tortuga and as for the Stereo Coffee I'll leave it for Chris to answer as I'm not an expert on the designs.

pure sound

19-06-2014, 09:14

Marco

19-06-2014, 09:36

Strange interpretation guys! Having been 'here' in the past when they say it 'expires on xx/xx/xx' they generally mean it 'expires on xx/xx/xx' ;)

Indeed. However, we don't know if that expiry date has since been extended and allowed up until the next EU hearing (without it having been stipulated in the outlining of the directive), due to the fact that research into Cadmium-free technology is still in progress, and so no substitutes for it yet exist.

*That* is what needs to be clarified.

The use of the term 'professional audio equipment' may be irrelevant now anyhow as I think RoHS 2 makes no distinction between EEE (Electrical and Electronic Equipment) for professional or consumer use.

I suspect that is the case, which once we ascertain whether or not it is true, along with if the exemption date has been extended and allowed up until the next EU hearing, will bring the current argument to an end about the legality of the use of LDRs in audio equipment inside the EU.

As an aside, here's a UK company currently supplying LDRs:

http://www.jprelec.co.uk/store.asp/c=1495/Miniature-Low-Cost-LDR

Marco.

Marco

19-06-2014, 09:38

Hi Guy,

Marco. The interesting comparison for you would not necessarily be your 'active' Croft vs a 'passive' LDR pre but rather incorporating an LDR volume control into the Croft & comparing that with the pot that was in there previously.

Indeed... That is exactly the purpose of the exercise and what I intend to do! :)

Marco.

anubisgrau

19-06-2014, 09:48

Marco. The interesting comparison for you would not necessarily be your 'active' Croft vs a 'passive' LDR pre but rather incorporating an LDR volume control into the Croft & comparing that with the pot that was in there previously.

i'm afraid that no pot existing can hold any comparison with a LDR.... i've had numerous tests here with various LDR, RVC, TVC and AVC - a properly done LDR is possibly the most transparent volume control you can get, slagle's AVC may have an edge in musicality but there's areas where LDR clearly betters it (transparency and detail)...

Marco

19-06-2014, 09:55

That's good news, Gordan, and makes me quite excited at the prospect of incorporating one into the Croft!

Marco.

Marco

19-06-2014, 10:46

The other point worth highlighting, in reference to this (noting the emboldened text):

I presume then that means that Cadmium in photoresistors, for analogue optocouplers, applied in electrical and electronic/audio equipment, was allowed before 31st December 2013, and so any stocks of LDR-based audio equipment belonging from that period would not be liable under the current expiration of the exemption from the ROHS directive?

...is that one wonders then when 'agenda-boy', elsewhere, in terms of LDRs, I quote: "investigated the product design thoroughly"?

Because if it was before 31st December 2013 then, contrary to his ramblings, their use in the EU at that point was allowed, and so there was nothing stopping him from trying them in his amplifier designs! ;)

Marco.

pure sound

19-06-2014, 10:51

i'm afraid that no pot existing can hold any comparison with a LDR.... i've had numerous tests here with various LDR, RVC, TVC and AVC - a properly done LDR is possibly the most transparent volume control you can get, slagle's AVC may have an edge in musicality but there's areas where LDR clearly betters it (transparency and detail)...

I'm inclined to think that how the adjacent active circuitry is implemented has far more influence on the quality of the end result.

Marco

19-06-2014, 10:56

Indeed, but I guess that all else being equal within the design of an amplifier, it seems likely that an LDR would be better than any pot or stepped attenuator, which is what I intend to find out :)

Marco.

Firebottle

19-06-2014, 11:26

r100

19-06-2014, 11:30

I really don't know what all the fuss is about the Cadmium in the LDR's.. Cadmium is everywhere, in batteries, food, tobacco smoke, drinking water, solar panels, etc., etc. No one in his right mind is going to eat his amp or light it up to smoke it ! But then you never know !

It is important to recycle the equipment properly at EOL. I am sure more toys with batteries containing Cd end up in landfills than any of these LDR based amps ever will.

I have been eyeing this type of VC for a while and will not be put off by any source of (dis)information or by vague EU regulations that no one is capable of interpreting unequivocally. The Tortuga amp has autocalibrating software that takes care of an eveventual drift of the LDR's specs :-) what more would you want ? oh, yes, a remote .. it has !

Marco

19-06-2014, 11:31

Rather hilariously, 'agenda-boy' is now backtracking, stating that, I quote: "according to my search of the regs they were illegal...", implying that he may have misinterpreted the regs and been wrong about the illegality of LDRs, during the time when he "investigated their product design thoroughly", which is quite a come down from shouting from the rooftops, like a man demented, that LDRs being illegal was indeed an undisputable FACT! :lol:

Now, instead of the big hoo-hah surrounding their supposed illegality, he's made up a previously unmentioned list of reasons why apparently he didn't make an LDR, outlined below:

1/ they are impracticable for stereo use as they cannot make matching pair.
2/ if you do spend loads of time matching pairs then they drift with age and cock it all up again
3/ they are prone to failure
4/ the Cadmium thing is not something I wish to get involved with mainly because it requires a separately set up solder station with fume extraction ventilation and safety measures that I haven't got the room or the time to get involved with.
5/ according to my search of the regs they were illegal, as #1 my usage was not for professional use, #2 no matter what the exemptions there was still end of life disposal problems in the future and the whole legality of use was a typical EU fudge and cock up."

Why didn't he mention any of that before?? The only reason he gave previously for not making an LDR was because he presumed that they were illegal. He's only listing these other reasons now because he has to come up with something to try and cover up his mistake! :eyebrows:

That's what you get for shouting your mouth off like a tit, before being aware of ALL of the facts!! He did the same thing with his accusations about my experience with the Technics SL-P1200 CD player, and whether or not it was sold for domestic use, and later was proven wrong, and so now the old tit is forced once again to eat humble pie......

One of these days he'll learn to keep his big mouth shut until he's 100% sure of his facts! ;)

Marco.

Light Dependant Resistor

19-06-2014, 11:31

That would be good as I can't locate the link your referred to...

I have found what the EU refer to as their recast document which is available here: http://eur-lex.europa.eu/search.html?qid=1403173435566&text=directive%202011/65/eu&scope=EURLEX&type=quick&lang=en&page=4
you then on page 3 find the document 32012L0051 which is the annex 111 note 40 carrying date of expiry in Dec 2013, however the 32011L0065 reference document is on page 4 and their letter I posted on this thread, I interpret is meaning reference to 8(b) on page 103 Cadmium and its compounds in electrical contacts being given exception with no current date expiry criteria, which is not quite as precise as the former document with description with respect to audio coupling LDR's . If I can find anything further that assists I will do so.

Cheers / Chris

r100

19-06-2014, 11:42

forget points 1 and 2. They still havn't grasped that SOFTWARE is required. point 3 is sorted by the modular design and point 4 and 5, well...

awkwardbydesign

19-06-2014, 11:48

Marco

19-06-2014, 11:57

Now agenda-boy says:

Go back to the beginning of our ref here to LDRs and you will see my priority, which pretty much matches with the last post.

Where previously he said:

Again I state that I have never heard a LDR based pre-amp. The illegality was enough to turn me off. My "thorough" investigation was into the design and the concept and the components used. Why the hell should I want to break the law by importing or building one.

Sorry, I don't see any mention there of points 1-5, which apparently were 'your priority'! The SOLE reason you gave was their supposed illegality. Deluded, mate, doesn't even scratch the surface.....

Anyway, that's enough of this now, as it's no fun destroying someone's argument who quite clearly doesn't have the capacity to remember what's been written and what hasn't!

:wave:

Marco.

Marco

19-06-2014, 11:59

Marco, The main reason I am using this forum more, is because the other place has the owner and his friends ignoring the rules, yet penalising anyone else. I do hope I don't have to move on again for the same reason.

Nope... Like I said before, sometimes in life, regardless of anything else, things need challenging. That done now, it's business as usual, so please accept my apologies :)

Marco.

DSJR

19-06-2014, 12:34

I still feel you have to go a heck of a long way to beat a couple of decent stepped attenuators with inputs and outputs matched as carefully as possible to the partnering gear. Apologies for the ignorance, but some truly wonderful recordings have been achieved over the decades using hundreds of feet of cable, mixing desks in the analogue domain with gain, L/R panning and TONE ALTERATION to each input channel, let alone the hundreds of op-amps and out-board effects before the signal reaches the master recorder. Granny sucking eggs I'm sure, but thought this ought to be mentioned just to put a little perspective back in.

Marco, with respect, you know as well as I do that if anyone was looking for a passive preamp here, the vast majority would look little further than a Tisbury, as the price seems fair on the face of it :) The NVA costs substantially more and would be more for a permanent system based around the matching amps I strongly suspect.

NRG

19-06-2014, 12:54

I have found what the EU refer to as their recast document which is available here: http://eur-lex.europa.eu/search.html?qid=1403173435566&text=directive%202011/65/eu&scope=EURLEX&type=quick&lang=en&page=4
you then on page 3 find the document 32012L0051 which is the annex 111 note 40 carrying date of expiry in Dec 2013, however the 32011L0065 reference document is on page 4 and their letter I posted on this thread, I interpret is meaning reference to 8(b) on page 103 Cadmium and its compounds in electrical contacts being given exception with no current date expiry criteria, which is not quite as precise as the former document with description with respect to audio coupling LDR's . If I can find anything further that assists I will do so.

Cheers / Chris

Chris, you need to seek further clarification. 8(b) Cadmium and its compounds in electrical contacts is vague at best and the assumption it applies to LDRs extremely tenuous. These documents usually spell things out very clearly and it would be unwise IMHO to start interpreting or second guessing their true meaning.

Macca

19-06-2014, 12:54

Dave - there is not really any comparison between a Tisbury and these LDR pre-amps.

TortugaRanger

19-06-2014, 13:31

1/ they are impracticable for stereo use as they cannot make matching pair.
2/ if you do spend loads of time matching pairs then they drift with age and cock it all up again
3/ they are prone to failure

With respect to these 3 points mentioned a few posts back, I can offer the following perspective having gone through several LDR design iterations.

In brief, designing with LDRs is a PITA. There's considerable variability between each individual LDR even of the same make/model. They are highly nonlinear especially over a wider resistance range. Given a choice, it's a rare bird that would willingly choose to work with highly variable nonlinear components in audio equipment design. So why do it? Because it's worth it if you're seeking the best possible audio experience. If you've spent some time around LDR preamps you get the joke pretty quickly. For example, I just had a customer tell me he's selling his $10k tube preamp after auditioning our LDR passive.

As with all analog components, LDRs will drift. LDRs are actually 2 analog components (photoresistor & LED) in an integral package. Most drift just a little. Some quite a lot. If you start with a decently matched set, a little drift isn't a big deal, especially if they all more or less drift similarly. Iv'e had an LDR preamp unit running for several years with no discernible drift that matters. But as I've found out, you can't count on that.

The first version of our LDR passive pre-amp design was entirely dependent on starting with matched sets of LDRs. We had to characterize every LDR over the full resistance range we needed. These tests results went into a database. We'd test 50-100 LDRs at a time. Then we would take that data and run it through a sorting algorithm to select the 4 or 8 best matched LDRs and use those in our next build. A lot of effort went into test rigs, data acquisition, and post-test data processing. We had to store each tested LDR with its own ID tag. Did I mention PITA?

In our second generation design, we still tested each LDR but applied a very different approach where we no longer needed perfectly matched LDRs. Instead, we simply picked pairs of test data points from each LDR that yielded the necessary dB attenuation setting for each volume step for each channel and placed those settings into a table used to drive each LDR at each volume step. Of course this was only possible because our design utilizes a software based digital microcontroller that drives the analog circuitry which regulates each individual LDR. But even with this approach, we had to custom test and calibrate each pre-amp build and store the resulting test data in our IT system. If any software changes needed to made to a customer's unit we had to utilize that original test data. If the LDRs drifted too much, the unit would need to be sent back for retesting and recalibration. This didn't happen very often but once in a while is frankly once too often.

With our third and most recent generation design ("V2"), we got ambitious and made the leap to self-contained auto-calibration where the preamp continuously recalibrates each LDR against a programmed dB attenuation schedule. No pre-matching or testing. Just plug in 4 LDRs and less than 10 minutes later it's ready to go. If one LDR happens to be too far out of spec to calibrate properly or just fails, you pop it out and plug in a replacement, wait 10 minutes and you're back in business. This is a more complex design, involves 12 bit DACs and ADCs, and consequently costs more, but it's completely software driven and the software can be updated via a USB port and a PC. We plan on selling high end finished units and want our customers to know they're getting a great long-term value.

To sum it up, I generally agree with the first 2 points but they can be successfully mitigated if not totally overcome. It's called engineering.

On the last point, I have to disagree. My own experience suggests maybe 1% of the LDRs we use are prone to infant mortality and there are ways of culling those out. The rest will likely live for several 10's of thousands of hours. Kind of like tubes only better.

Cheers, :D
Morten

Light Dependant Resistor

19-06-2014, 13:47

Chris, you need to seek further clarification. 8(b) Cadmium and its compounds in electrical contacts is vague at best and the assumption it applies to LDRs extremely tenuous. These documents usually spell things out very clearly and it would be unwise IMHO to start interpreting or second guessing their true meaning.

The EU have a redraft as I understand organized commencing 02/07 and finishing 29/07. As I said I am trying to also understand their letter - matching it to what is available on their website, I would much rather, like Morten to be talking about our preamp . Cheers / Chris

awkwardbydesign

19-06-2014, 14:09

Firebottle

19-06-2014, 14:11

It's called engineering. I like it :thumbsup: but then I would as I'm an engineer.

On the last point, I have to disagree. My own experience suggests maybe 1% of the LDRs we use are prone to infant mortality and there are ways of culling those out. The rest will likely live for several 10's of thousands of hours. Kind of like tubes only better.

Cheers, :D
Morten[/FONT]
A far as reliability goes there must be millions of optocouplers in service worldwide in various comms links> I've never come across a failed one, unless it's a lightning strike :eek:

:cool: Alan

TortugaRanger

19-06-2014, 14:32

Interesting post by Morten. I read the technical stuff on his website, but the extra info is fascinating. So if LDR attenuators are made without this self calibration, will they stay within spec long enough to be worth bothering with? Over to you, Chris. :) Especially as yours is the one I can afford, at the moment!

I'll even pipe in on this one since it's a fair question and nearly nearly all of our existing customers currently have non-self-calibrating designs. You can expect very decent performance from an LDR preamp with matched LDRs but there's no doubt they're susceptible to drift over time. We made the decision to go with auto-cal because it offered long term assurance and removed this niggling concern but at a price. But you can get very satisfying performance from LDR designs without auto-cal. I would never suggest otherwise.

Light Dependant Resistor

19-06-2014, 14:40

Interesting post by Morten. I read the technical stuff on his website, but the extra info is fascinating. So if LDR attenuators are made without this self calibration, will they stay within spec long enough to be worth bothering with?
Over to you, Chris. :) Especially as yours is the one I can afford, at the moment!

Hi Richard
Yes, a preamp still in service today built 4 years ago containing the matched NSL32SR2 not the S variety maintains its same resistance, and sounds excellent. As usual any LDR board we do can be updated with a new control board and we supply you with the updated control board free. We need however to get over this hurdle of the National Instruments office UK clearing ongoing sales, described at post 110 lets give them time to assess and reply first before orders are placed. You will hear about it, as soon as we know on this same thread.:)

Cheers / Chris

Marco

19-06-2014, 14:58

Well get on with it..........:please:

I'm very much interested in this thread as I'd like to incorporate an LDR level control into an ultimate line level valve preamp>
All the better for VFM too,

:cool: Alan

Lol... Well, I believe that Anthony TD's going to be building an LDR, ASAP, which he'll be testing for accuracy in comparison with his current benchmark stepped attenuators. The results of that test (after I assess the respective sonic performance of both) will determine whether an LDR ends up inside the Croft, so watch this space! :)

Marco.

awkwardbydesign

19-06-2014, 16:19

Hi Richard
We need however to get over this hurdle of the National Instruments office UK clearing ongoing sales, described at post 110 lets give them time to assess and reply first before orders are placed. You will hear about it, as soon as we know on this same thread.:)

Cheers / Chris
Damn, stop teasing me! I was about to order one!

anubisgrau

19-06-2014, 19:01

With our third and most recent generation design ("V2"), we got ambitious and made the leap to self-contained auto-calibration where the preamp continuously recalibrates each LDR against a programmed dB attenuation schedule. No pre-matching or testing. Just plug in 4 LDRs and less than 10 minutes later it's ready to go. If one LDR happens to be too far out of spec to calibrate properly or just fails, you pop it out and plug in a replacement, wait 10 minutes and you're back in business. This is a more complex design, involves 12 bit DACs and ADCs, and consequently costs more, but it's completely software driven and the software can be updated via a USB port and a PC. We plan on selling high end finished units and want our customers to know they're getting a great long-term value.

in a nutshell, this is exactly how the Myth LDR preamp functions since 2009....:)

r100

19-06-2014, 21:42

how does it sound ?

Soulman

19-06-2014, 22:19

Well I do't know about the legal side but can comment on my, brief, experience with a LDR passive pre. After just a short time it sounds amazing, I'm comparing i to a £4k Graaf 13.5b pre, which does many things wonderfully but the LDR has incredible bass and dynamics, along with great rendition of voices. My one criticism at the moment would be a slight lack of height to the soundstage and some treble seems a little recessed, as I sad this is in cmarison to a highly thought of valve pre.

Figlet108

20-06-2014, 00:17

Well I've been having a great evening enjoying the music from the LDR - in this case the Tortuga. I bought an apple remote today to control the LDR and 'testing' the remote was a great excuse to ignore all the football and listen to music.
While listening I have been catching up with all the various discussion across the web about LDRs - past and present. Some positive and evangelical "best pre ever.. blah blah", others negative worrying about the theoretical problems of the circuit, even though it's clear the posters have never actually owned or heard an LDR, others making out that they are so dangerous that even looking at them will likely cause instant death to you, your family and your neighbours. And in the end it's all just bullshit words and egos, and compared to the actual experience of some quality time with the hifi listening to sublime music, a complete waste of time.

.

awkwardbydesign

20-06-2014, 07:22

Macca

20-06-2014, 07:42

It turns out that without realising it me and Macca's 'bake off' which started this thread, did actually rise to the challenge laid down in that post. Because what neither of us mentioned before was that I also brought over my NVA TSS amp for Macca to experience as he'd never heard NVA power amps before. And we did compare the P90SA and the LDRs with the NVA amp, and we BOTH agreed that on that occasion and in that environment the LDRs were better.

.

I recall we tried the TSS with the Stereo Coffee pre-amp but I have to say I don't think we actually ran a comparison with the P90SA/TSS combo although that may be my memory playing up. Certainly the best combo of what we tried was the Tortuga/XTZ combo which was, frankly, joke good.

Figlet108

20-06-2014, 07:47

Well done for missing the football! As soon as they are cleared I will order one of Chris's LDR pres. I have enough bits for a psu and case, etc, so cheap enough just to try it out. I will hold you personally responsible if I don't like it, mind! :donk:

Tell you what Richard, if you don't like the LDR, I'll buy it off you for a fair price. :)
And do let me know if there's any other decision you want to make in life and I'll see if I can indemnify you - you know if you have a bad meal in a restaurant or a holiday goes bad... :D

Figlet108

20-06-2014, 07:52

I recall we tried the TSS with the Stereo Coffee pre-amp but I have to say I don't think we actually ran a comparison with the P90SA/TSS combo although that may be my memory playing up. Certainly the best combo of what we tried was the Tortuga/XTZ combo which was, frankly, joke good.

Yep we did, but very briefly as we already preferred your XTZ vs the TSS so it wasn't a very interesting combo by then...

Edit: anyway,we can do 'the challenge' again at my place next weekend when you and Marco come over.

awkwardbydesign

20-06-2014, 09:06

Tell you what Richard, if you don't like the LDR, I'll buy it off you for a fair price. :)
And do let me know if there's any other decision you want to make in life and I'll see if I can indemnify you - you know if you have a bad meal in a restaurant or a holiday goes bad... :D
Be careful what you promise...........

Macca

21-06-2014, 08:57

Soulman

21-06-2014, 17:04

anthonyTD

21-06-2014, 17:43

Quite agree with you Des! :(
However, it is pretty easy to get drawn into petty squables, especially when you have members here' and on other forums with diffrent views to yours, i have been guilty of this on more than a few instances, although i do try much harder to turn the other cheek these days, lifes too short! :)
A...

All this though means little and I am left with a slightly sour taste in my mouth having read this thread and from it looked further into the animosity I see here and elsewhere. I can't understand how a love of music and its reproduction can lead to such feelings, it's supposed to be fun!

Figlet108

21-06-2014, 22:36

Ibought a LDR without first reading fully into it. I await with interest to find out the legality of them in the UK (or EU for that matter), my initial impression, remember this is my first listen to a passive, is one of astonishment (I understand my power amp is designed with passives in mind) at the clarity, deep bass and musicality coming from my speakers.

All this though means little and I am left with a slightly sour taste in my mouth having read this thread and from it looked further into the animosity I see here and elsewhere. I can't understand how a love of music and its reproduction can lead to such feelings, it's supposed to be fun!

Des, it's great to hear that you're enjoying your LDR as much as I am mine, and it's exactly the point of this thread: I also bought an LDR, on a bit of a whim as it was cheap and because the theory of LDRs sounded interesting, and was also blown away by what I was hearing. So I started this thread to share my enthusiasm with fellow enthusiasts, just as many have done before on hifi forums.

And as you and a growing number of others have independently found and are independently finding, I'm not making this stuff up - LDRs sound very good and are a revelation.

Your quote in bold is explained very simply: for some, who are in the industry, it is not about fun and a love of music, it's about business, reputation, power and politics. It's very difficult these days on open forums to know what agendas and motivations people have for posting things and so as a matter of course I treat anything said by those in the industry or aspiring to be in the industry with caution and suspicion, especially when it's clearly self-serving.

As for the legality *FOR YOU* for having bought an LDR, there is no issue whatsoever. You are not a business importing LDRs for resale. You are an end user. If selling LDRs is illegal in the UK, then it's the seller that is breaking the law not you.

So just enjoy your LDR and forget about all the nonsense.

Figlet108

21-06-2014, 23:00

I have removed the off-topic posts from this thread.

Members are cordially reminded that personal beefs with anyone, be it other members, manufacturers, the milkman or anyone should be resolved privately and not on this audio forum.

Thank you for your understanding.

Fair enough Martin. In my case I thought that a reference to the archive site specifically about LDRs and not about anything personal would be acceptable.

Let me see if I can make my 2 points again as simply and directly as possible and without contravening any AOS rules:

1) NVA have only started spreading what is in my opinion FUD (Fear Uncertainty and Doubt) regarding LDRs after our bake off where we found them to be better than the flagship NVA preamp.
In previous years when LDRs were mentioned on forums there was never any mention of health or legal issues.
This point is neither personal nor off-topic. AOS has a duty in my opinion to help protect its members from deceitful intentions and ill-will in the industry that hinders their members enjoyment of their hobby. I believe my argument above shows that this is likely the case here.
And if anyone was to read all the LDR related posts on that archive forum they would get a very different impression of LDRs than is being portrayed now by NVA.

2) A number of years ago NVA made a bold and public challenge that, (and I paraphrase), no LDR could compare to its stepped attenuator pre when paired with an NVA power amp.
I state right here that that challenge was met and both the Stereo Coffee and Tortuga LDR were better than an NVA P90SA on that day that we tested them.
If there is any doubt about that bake off, we can carry out that same challenge again next weekend.
Since this was a publicly made challenge to the hifi community and since this is an LDR thread, I again do not think it's inappropriate to mention it here.

Marco

21-06-2014, 23:14

If there is any doubt about that bake off, we can carry out that same challenge again next weekend.

I look forward to that, and Macca can be the unbiased judge of the outcome, in terms of having any 'gripes' against NVA equipment or the company owner. Regardless, as always, I will simply tell it as I hear it, even if the Croft ends up at the bottom of the pile.

Marco.

wee tee cee

22-06-2014, 00:39

Light Dependant Resistor

22-06-2014, 01:03

If selling LDRs is illegal in the UK, then it's the seller that is breaking the law not you.

Which is why we have sought clarification from the National Instruments Office UK, and have already suspended UK sales pending that outcome explained at Post 110.

The answer that was provided by the EU that can to a degree be viewed as the parent body that NIO UK gathers information from and consults, has advised 19/06/14

' The Commission Directive 2012/51/EU has enabled the use of cadmium in photoresistors for analogue optocouplers as an exemption from the ROHS directive. Therefore, indeed, the use of
cadmium in photoresistors for analogue optocouplers is currently allowed as there are no other substitutes.

As soon as more information becomes available from NIO UK we will advise. :)

Cheers / Chris

Light Dependant Resistor

22-06-2014, 01:31

I noted the LDR kit requires a 12v supply. Could this be powered by a battery ? If so what would I need to do!!!! I run a DAC and two t amp mono blocks off a big car battery, could an additional spur supply this board. Cant help but think this could make a nice combo........

Hi
Yes battery supplies work very well with our kit, you need to house the 12 volt battery appropriately to consider ventilation. A charger can be connected when charging and disconnected when listening. A suggested circuit setting voltage and current regulated is below for a 1.2 AH battery. A big car battery as you describe though requires a dedicated car battery charger as it uses far higher current. In our small charger battery implementation the switch isolates the charger circuit from the battery supplying power. The earth connection to star earth also being isolated during charge assume the switch as double pole . The connection to J2 control board is shown for clarity, as it is an option with our kit to connect or disconnect J2 as being 0v.12694 Happy to assist you with your actual requirements as a spur which is a great idea.

wee tee cee

22-06-2014, 02:16

Light Dependant Resistor

22-06-2014, 04:27

Chris,
Thanks for that....a few of the troops run battery set ups, myself utilising solar chargers. Just thought this would be a nice complement to the no complication approach. Venting is sorted as my battery is in the cellar bellow my listening room.
Off the grid music....majik!!!!!

Hi Tony
Excellent power generation, and really nice sound as a result. Solar is a nice answer for charging, similarly a listen charge switch can route delivery of current straight from and during charge to the battery source. A 1.2AH size which is quite a small battery lasts for 500 hrs or more without charge, our LDR circuit is very economical with power. Remember though with LDR's best to leave your volume control at 1/3 when off to bed, as the internal illumination inside them is on more so with respect to the shunt pair, when volume is fully off.

Although you have your solar sorted, other readers may like to leave a solar panel semi permanently on, and we can accommodate this too.
Cheers / Chris

Gordon Steadman

22-06-2014, 06:10

It's very difficult these days on open forums to know what agendas and motivations people have for posting things and so as a matter of course I treat anything said by those in the industry or aspiring to be in the industry with caution and suspicion, especially when it's clearly self-serving.

Which is precisely why I distrust anything you say on this subject given your history. Please stop talking about NVA in this connection and stick to LDRs, your next post wriggles around the rules which were put in place to avoid exactly what you are doing.

Macca

22-06-2014, 07:26

Which is precisely why I distrust anything you say on this subject given your history. Please stop talking about NVA in this connection and stick to LDRs, your next post wriggles around the rules which were put in place to avoid exactly what you are doing.

The thing is Gordon that we do need to have some comparison for the LDR pre-amps to be based against. As these are passive pre-amps then it does make sense to compare them to other passive pre-amps and a fair case can be made that the NVA P90SA is the best stepped attenuator pre-amp around. Certainly its introduction into my system catapulted the sound into the 'high end' when compared to other pre-amps both active and passive therefore it is a legitimate benchmark for me and for Jason since he has also owned one in the past. We will also be comparing performance with Marco's Croft pre-amp which is effectively a highly-tuned bespoke unit and could be fairly said to represent the best of valve-powered pre-amps. We are hi-fi enthusiasts and this is what we do :)

Gordon Steadman

22-06-2014, 07:32

Macca

22-06-2014, 07:42

guy

22-06-2014, 07:53

The thing is Gordon that we do need to have some comparison for the LDR pre-amps to be based against. As these are passive pre-amps then it does make sense to compare them to other passive pre-amps and a fair case can be made that the NVA P90SA is the best stepped attenuator pre-amp around. Certainly its introduction into my system catapulted the sound into the 'high end' when compared to other pre-amps both active and passive therefore it is a legitimate benchmark for me and for Jason since he has also owned one in the past. We will also be comparing performance with Marco's Croft pre-amp which is effectively a highly-tuned bespoke unit and could be fairly said to represent the best of valve-powered pre-amps. We are hi-fi enthusiasts and this is what we do :)

Well done Gordon and Macca,

Some balance and sense at last. following Jason's latest post I have had a look at the archive which he refers to and it is quite obvious that the challenge refers to a couple of products called "Eva" and "Lightspeed".

Reading between the lines it also seems that at that time Jason was in agreement - apologies if I have misinterpreted your position three years ago, but it is difficult to interpret the archive as someone has deleted all your posts (and quite a few others by the look of it!).

However, "onward and upward". It will be interesting to hear Marco's and Macca's thoughts on the comparison with new products, as Macca said NVA do make a mighty fine passive (and I speak as a recent convert to the whole passive concept: NVA P50 and Phono 2 combination - beautiful).

On the safety issue, I think that there is a certain amount exaggeration going on. No one, to my knowledge has said that just looking at a photo cell will kill the wife, kids and neighbours. It has been pointed out that there is confusion over the legality of importation and "LDR" is quite rightly urging a cautious approach regarding safety, the environment and the law.

Tim

22-06-2014, 07:59

I'm not a 'rules is rules' type person but it is never the less extremely irritating to see there are rules for some and not for others, depending on where they are coming from.
+1

Gordon Steadman

22-06-2014, 07:59

Gordon I agree with what you say and I think everyone and not just Jason needs to view this dispassionately so that we can concentrate on the more interesting side of this which is to evaluate the LDR pre-amps in context.

Maybe we should consider a Wigwam style 'pub car park' where all gloves are off and anyone can be as obnoxious as they like to each other so the rest of us can get on and ignore them.

As you say, this place should be about discussing hi-fi and music and not personalities.

Macca

22-06-2014, 08:24

Maybe we should consider a Wigwam style 'pub car park' where all gloves are off and anyone can be as obnoxious as they like to each other so the rest of us can get on and ignore them.

As you say, this place should be about discussing hi-fi and music and not personalities.

You are the second person to suggest that to me in as many days. I don't want that - it lowers the tone and attracts the wrong element. What we want here is a high-class audio site that attracts genuine enthusiasts and not keyboard warriors or people who have some petty grievance - I genuinely believe that aside from a few sad individuals that no-one else cares a damn about such childishness! I don't want to see any further agendas on display from anyone, this is not the place for it.

Gordon Steadman

22-06-2014, 08:40

You are the second person to suggest that to me in as many days. I don't want that - it lowers the tone and attracts the wrong element. What we want here is a high-class audio site that attracts genuine enthusiasts and not keyboard warriors or people who have some petty grievance - I genuinely believe that aside from a few sad individuals that no-one else cares a damn about such childishness! I don't want to see any further agendas on display from anyone, this is not the place for it.

Indeed, it wasn't a serious suggestion. People seem to find quite enough ways of being unpleasant without offering an official pathway. I joined Wam only to be put off by the general air of schoolboy mentality.

Soulman

22-06-2014, 08:44

Well done Gordon and Macca,

Some balance and sense at last. following Jason's latest post I have had a look at the archive which he refers to and it is quite obvious that the challenge refers to a couple of products called "Eva" and "Lightspeed".

Reading between the lines it also seems that at that time Jason was in agreement - apologies if I have misinterpreted your position three years ago, but it is difficult to interpret the archive as someone has deleted all your posts (and quite a few others by the look of it!).

However, "onward and upward". It will be interesting to hear Marco's and Macca's thoughts on the comparison with new products, as Macca said NVA do make a mighty fine passive (and I speak as a recent convert to the whole passive concept: NVA P50 and Phono 2 combination - beautiful).

On the safety issue, I think that there is a certain amount exaggeration going on. No one, to my knowledge has said that just looking at a photo cell will kill the wife, kids and neighbours. It has been pointed out that there is confusion over the legality of importation and "LDR" is quite rightly urging a cautious approach regarding safety, the environment and the law.

I believe it was Jason himself who "deleted all of his posts", I really didn't want to get involved with this, my interest in hifi fora(?) is to learn, see new ways of enjoying music on a budget and exploring new music. Much of this has been achieved but I'm always open to considering new kit with my own ears and said manufacturer, NVA, are on my list to try as I feel they'll work well with my speakers. All of this personal hostility reflects badly on this forum and some of its members and secondly will scare off new members, which every forum needs to flourish.

DSJR

22-06-2014, 08:51

I look forward to that, and Macca can be the unbiased judge of the outcome, in terms of having any 'gripes' against NVA equipment or the company owner. Regardless, as always, I will simply tell it as I hear it, even if the Croft ends up at the bottom of the pile.

Marco.

Marco, can't find the comment you made about putting an LDR circuit in your Croft if you find it better. I do hope you were jesting in saying that as it would be far better to have a nice new custom case made for any replacement for the Croft and either put the Croft away, or sell it to someone who can enjoy it as-is. I'd have thought one of Anthony's 'Grounded Grid' preamps may have been the way to go in your case, but I digress (has Anthony ever shipped one of these to you to try?). It's been said that the LDR preamps of a few years ago are no longer in production (reliability and channel-balance drifting issues have been sited), but maybe this is now a thing of the past?

To get a cheapo taste of a passive, why not look at and borrow? the good old Tisbury, which is fairly priced for what it offers? I know you'd never want to keep it as it only uses standard bits, but it would show I think what this kind of volume controlling would do - in your current system?

Macca

22-06-2014, 08:53

I. All of this personal hostility reflects badly on this forum and some of its members and secondly will scare off new members, which every forum needs to flourish.

Exactly, Des.

I'd like to remind members that this thread is for discussing pre-amps so please no more posts here that are off-topic or contain off-topic elements. If anyone would like to discuss how the forum is run or moderated then please start a new thread in the Critic's Corner section. Thank you for your co-operation.

Marco

22-06-2014, 09:08

Marco, can't find the comment you made about putting an LDR circuit in your Croft if you find it better. I do hope you were jesting in saying that as it would be far better to have a nice new custom case made for any replacement for the Croft and either put the Croft away, or sell it to someone who can enjoy it as-is. I'd have thought one of Anthony's 'Grounded Grid' preamps may have been the way to go in your case, but I digress (has Anthony ever shipped one of these to you to try?). It's been said that the LDR preamps of a few years ago are no longer in production (reliability and channel-balance drifting issues have been sited), but maybe this is now a thing of the past?

To get a cheapo taste of a passive, why not look at and borrow? the good old Tisbury, which is fairly priced for what it offers? I know you'd never want to keep it as it only uses standard bits, but it would show I think what this kind of volume controlling would do - in your current system?

Hi Dave,

Yes I do intend to try an LDR in the Croft, as an alternative to the DACT stepped attenuator currently providing volume control duties, *providing* that after Anthony has built and tested the LDR, he considers it to be as accurate and reliable as the DACT.

Furthermore, the bake-off at Jason's, next Saturday, will I suspect provide me with more than an inkling as to how good an LDR is. Trust me, I am very happy indeed with the Croft, and so it will take something rather special to oust it, although replacing the whole preamp altogether with a passive design is unlikely. However, we'll see what happens. As ever, I remain open-minded.

I've tried a couple of Anthony's GG preamps, and enjoyed them very much, but ultimately still preferred my Croft. It's been up against umpteen top-notch preamps over the years and always held its own. I always enjoy testing my kit against other high-quality gear, as it's the only way you'll ever know how good it really is in the grand scheme of things.

I've never been one for hiding inside my comfort zone! ;)

Marco.

kininigin

22-06-2014, 09:24

Gordon I agree with what you say and I think everyone and not just Jason needs to view this dispassionately so that we can concentrate on the more interesting side of this which is to evaluate the LDR pre-amps in context.

+1 I am genuinely interested in the comparisons between the different pre-amps! Lets leave all the other nonsense behind,at least for the sake of your own dignity,if nothing else!

Ali Tait

22-06-2014, 09:33

You still use the phono stage in the Croft do you not Marco?

Marco

22-06-2014, 09:41

Yus - is that a problem? :)

Marco.

lurcher

22-06-2014, 10:08

Yus - is that a problem? :)

Marco.

I am guessing Ali's point was it will be a problem, if what you wanted to do was see what the LDR would sound like instead of the DACT. Without the phono stage you could have tried that by turning the croft vol up full and putting the LDR in front of it. The phono stage stops you from trying that.

Ali Tait

22-06-2014, 10:12

Yes, it had crossed my mind, though I guess you could try it with cd.

Marco

22-06-2014, 10:22

Ah, I see... Could you explain in layman's terms why the LDR can't be used with the Croft's built-in phono stage? If that's the case, then fitting one into the Croft will be a no-no.

However, if the LDR is better with CD, then I guess a separate standalone passive unit could be used for playing CD, and the Croft retained simply as a phono stage. We'll just have to see what happens, though, when the listening tests are carried out.

Marco.

lurcher

22-06-2014, 10:35

Ah, I see... Could you explain in layman's terms why the LDR can't be used with the Croft's built-in phono stage? If that's the case, then fitting one into the Croft will be a no-no.
Marco.

The way the insides of the croft are connected is

phono input -> phono stage -> input selector -> volume control -> preamp -> output

for phono and

CD input -> input selector -> volume control -> preamp -> output

To try the LDR in the first phono situation would require physically removing the DACT from the circuit and replacing with the LDR, can't be done without soldering. With the CD input something close can be done (assuming the DACT at full volume has no sonic affect)

input -> LDR -> cd input -> input selector -> volume control on full -> preamp -> output

anthonyTD

22-06-2014, 11:05

Hi Nick,
If i decide the LDR is worth trying with the croft, then i will physicaly remove the DACT attenuator from the circuit, and simply replace it with an LDR circuit, this way, the preamp should function as is' ie; with the DACT currently fitted. :)
A...
The way the insides of the croft are connected is

phono input -> phono stage -> input selector -> volume control -> preamp -> output

for phono and

CD input -> input selector -> volume control -> preamp -> output

To try the LDR in the first phono situation would require physically removing the DACT from the circuit and replacing with the LDR, can't be done without soldering. With the CD input something close can be done (assuming the DACT at full volume has no sonic affect)

input -> LDR -> cd input -> input selector -> volume control on full -> preamp -> output

Marco

22-06-2014, 11:09

Ah, alles klar! :)

Marco.

lurcher

22-06-2014, 12:09

Ahh, ok, I thought Marco was talking about just comparing the Croft with an existing LDR preamp.

TortugaRanger

22-06-2014, 15:04

The way the insides of the croft are connected is

phono input -> phono stage -> input selector -> volume control -> preamp -> output

for phono and

CD input -> input selector -> volume control -> preamp -> output

To try the LDR in the first phono situation would require physically removing the DACT from the circuit and replacing with the LDR, can't be done without soldering. With the CD input something close can be done (assuming the DACT at full volume has no sonic affect)

input -> LDR -> cd input -> input selector -> volume control on full -> preamp -> output

We often receive inquiries similar to this one. If you're not ready to do surgery on your existing pre (Croft in this instance) then you can try putting the LDR both in front of the Croft or after the Croft and leaving the Croft's volume set at max. The benefit of putting the LDR in front is the Croft remains as a buffer stage but as noted this may not be work well with a phono input to the LDR (although I've not tried this). Putting the LDR downstream of the Croft will allow you to get a better sense of how the LDR would normally work insofar as a passive is usually located downstream of the source and isn't buffered by definition. Plus you can use the Croft's phono stage with the LDR located downstream. If all goes well you can always decide later to bypass the Crofts VC/preamp altogether thus allowing retention of the phono stage but making it more of a true passive.

anthonyTD

22-06-2014, 18:09

No Worries Nick,
I think Marco is going to have a listen to an LDR, and take his Croft [in its current state] along for comparison, so that will be interesting! :) I have one of Chris's LDR circuits here at the moment, which i have been doing some tests with on the bench today, i will be putting it in my system for a listen once i have enclosed everything in some form of container. ;)
A...
Ahh, ok, I thought Marco was talking about just comparing the Croft with an existing LDR preamp.

awkwardbydesign

22-06-2014, 19:27

Maybe we should consider a Wigwam style 'pub car park' where all gloves are off and anyone can be as obnoxious as they like to each other so the rest of us can get on and ignore them.

Lets not. Or we could have the situation where you get abused in the carpark, banned, and then have an insulting image and signature added to your profile while you are banned and unable to respond or erase them. Which is why I am now here more than there!

Gordon Steadman

22-06-2014, 20:03

Lets not. Or we could have the situation where you get abused in the carpark, banned, and then have an insulting image and signature added to your profile while you are banned and unable to respond or erase them. Which is why I am now here more than there!
:lol:

Well, as I said to Macca, it wasn't a serious suggestion. I am quite anally retentive enough without having their influence drag me out into the pub carpark. The few comments I made over there were immediately mocked for being too sensitive for their sensitivities. Plus I didn't swear even once. No chance of being accepted.

BTH K10A

22-06-2014, 20:10

Maybe we should consider a Wigwam style 'pub car park' where all gloves are off and anyone can be as obnoxious as they like to each other so the rest of us can get on and ignore them.

As you say, this place should be about discussing hi-fi and music and not personalities.

Best to use the ignore option in your user settings. I've weeded out those who IMHO are idiots, trolls, bonkers or post comments mearly to serve another(s) agenda. :nono:

It's human nature that there will be conflicts and agenda's between individuals in a community and I would be surprised if I'm not on some ignore lists but thats good if it avoids conflict.

It works (even on this thread) for me. :)

Gordon Steadman

22-06-2014, 20:28

Best to use the ignore option in your user settings. I've weeded out those who IMHO are idiots, trolls, bonkers or post comments mearly to serve another(s) agenda. :nono:

It's human nature that there will be conflicts and agenda's between individuals in a community and I would be surprised if I'm not on some ignore lists but thats good if it avoids conflict.

It works (even on this thread) for me. :)

I hate to say it but we seem to have a bit of thread drift going here - again:lol:

Sorry about that Mr Moderator Sir.

Barry

22-06-2014, 20:57

Can we return to the thread now please? Macca has made it clear what we think about off-topic and ad hominem comments.

anthonyTD

23-06-2014, 07:57

:eek::lol:

Not lead-lined i hope.

anubisgrau

23-06-2014, 10:31

So, when we are burning all the Shindo gear in the UK for not being RoHS compliant?

r100

23-06-2014, 10:39

hmmm, I wouldn't burn them :eyebrows: those fumes would be even more toxic than the hardware :eek:

oh, I am looking forward to the feedback from the bake-off :)

anthonyTD

24-06-2014, 21:23

hi all,
Just thought I’d give a brief update of my first listen to the LDR preamp I have recently been testing, and evaluating.
The first thing that was obvious from the first few minuets of listening in my own system is how the music just flows, the immediacy and timing is remarkable, however, being a passive, I was initially a bit apprehensive about how the LDR would portray bass, I was perhaps expecting the drive and impact to be the weak point of this preamp, but I was pleasantly surprised, when there is real bass, whether it be a double bass, or a bass kick drum, the LDR reproduces it with effortless weight, and speed in a way that you would' and could' easily be fooled into thinking you were listening to a good active circuit, and not a passive. Piano and snare drum again are uncannily real, with crisp, immediate leading edges, with not a hint of slur or lush, that just begs you to search your music collection for more... I will be doing some more intense listening over the next few days to some albums that I know well, this time paying firm attention to male and female voices, just to confirm my first impressions, but from my brief' but very informative first few hours of listening, I am very impressed, which is something I never thought I would ever be saying about a passive after many years of using well designed actives! :)
A…

Marco

24-06-2014, 21:50

Most interesting indeed..... That seems to confirm what many others have been sayiing. So do you reckon it'll work well in the Croft? :)

Marco.

anthonyTD

25-06-2014, 08:18

Hi Marco,
I cant see why not, However' it will be interesting to hear about your own experiences after your meet up...
Most interesting indeed..... That seems to confirm what many others have been sayiing. So do you reckon it'll work well in the Croft? :)

Marco.

Marco

25-06-2014, 08:26

Indeed - and I'm looking forward to that :)

However, what I was getting at was whether your gut feeling was if the LDR was better (more accurate at fulfilling its function as a volume control) than the DACT....?

My main focus here is on potentially upgrading the performance of the Croft (via the fitting of an LDR), not necessarily comparing passive LDR preamps (or any others) with active valve preamps [no doubt interesting as that will be], as any *major* revelations on Saturday aside, I still expect to be using the Croft as my preamp of choice.

Marco.

anthonyTD

25-06-2014, 11:36

Yes, i understand where your coming from,
My reason for trying it as a passive first of all, and not combined in a preamp is simple, i wanted to hear it as is, with nothing influencing its performance well' as little as posible, i even used solid copper core cabling for the short lengths needed to the input and output sockets, without any insulation! My point was simple, yes, from memory, LDR's work much better than any passive mechanical volume control i have tried full stop, that includes the DACT switch, so, with that info in mind, the benefits of this passive experiment should transfer over into any active preamp it might be fitted in. I hope that i have made my findings a bit clearer now :)

Indeed - and I'm looking forward to that :)
However, what I was getting at was whether your gut feeling was if the LDR was better (more accurate at fulfilling its function as a volume control) than the DACT....?

My main focus here is on potentially upgrading the performance of the Croft (via the fitting of an LDR), not necessarily comparing passive LDR preamps (or any others) with active valve preamps [no doubt interesting as that will be], as any *major* revelations on Saturday aside, I still expect to be using the Croft as my preamp of choice.

Marco.

awkwardbydesign

25-06-2014, 14:20

The first thing that was obvious from the first few minuets of listening
:lol: Did it make you get up and dance?
But seriously, what power amp or amps is it feeding? I understand passives are sensitive to this (I use a Promitheus TVC), and if the input impedance of the power amp doesn't suit the pre then there are problems. My SS power amp is 100k, my cheap valve SE amp is 100k and my big Velleman kit amp started as 100k, but the later version was 33k. I am updating that, so I can pick 33, 47 or 100k. Should I stick with 100k? They all have enough gain for the TVC. Or am I being overly simplistic?

anthonyTD

25-06-2014, 15:04

Damn, thats what you get for letting auto correct take over!!! :eek::lol: Power amps are my own Soul 30 watt mono-blocks, input impedance is 47k, 100k should be no problem.
Hope this helps.
A...
:lol: Did it make you get up and dance?
But seriously, what power amp or amps is it feeding? I understand passives are sensitive to this (I use a Promitheus TVC), and if the input impedance of the power amp doesn't suit the pre then there are problems. My SS power amp is 100k, my cheap valve SE amp is 100k and my big Velleman kit amp started as 100k, but the later version was 33k. I am updating that, so I can pick 33, 47 or 100k. Should I stick with 100k? They all have enough gain for the TVC. Or am I being overly simplistic?

awkwardbydesign

25-06-2014, 16:26

Marco

26-06-2014, 06:21

My point was simple, yes, from memory, LDR's work much better than any passive mechanical volume control i have tried full stop, that includes the DACT switch, so, with that info in mind, the benefits of this passive experiment should transfer over into any active preamp it might be fitted in. I hope that i have made my findings a bit clearer now :)

Absoluto! *Now* I am excited! :eyebrows:

Marco.

awkwardbydesign

26-06-2014, 09:09

Never mind all this wittering on about how good they are, when can I bloody well order one?

Figlet108

27-06-2014, 13:57

Which is precisely why I distrust anything you say on this subject given your history. Please stop talking about NVA in this connection and stick to LDRs, your next post wriggles around the rules which were put in place to avoid exactly what you are doing.

Let's be very clear about why this thread was started and what it's about. It's about LDR pre amps and whether there is something fundamental about that technology that makes them better than any other pre amp technology (stepped attenuators, TVCs etc etc).
It's not about NVA or anyone connected to NVA. The fact that Macca happens to have an NVA pre amp, and the fact that he happened to buy a Stereo Coffee LDR when I did, and the fact that he wasn't able to get it assembled for a long time, and the fact that I was able to help him, and the fact that he lives near me, are ALL the conditions (almost all of which are out of my sphere of influence) that led to us comparing the LDR to an NVA product.

And since this thread is about LDRs any safety or legal information regarding LDRs is also relevant.
In addition, if ANYONE or ANY company regardless who they are, is trawling about the internet to any forum that they are not banned from and trying to put down LDRs and attack the livelihood of small independent LDR companies (like Stereo Coffee and Tortuga) out of questionable and professionally conflicting motives, then this is also relevant in this thread.

On the eve of tomorrow's bake off that will unfortunately again involve an NVA product I have 2 suggestions to try and diffuse the inevitable fallout.
1) Let's stop referring to the P90SA in tomorrow's bake-off as an NVA product and just refer to it as an Elma/Shinkoh stepped attenuator. After all there is very little that is 'NVA' about the P90SA, since the stepped attenuators used are off the shelf components and were neither designed or assembled by NVA.

2) Let's organise an AOS-only bake off (since the one Macca tried to organise clearly isn't going to happen under current circumstances) and have many other independent folks with no connections or agendas have a listen to all manner of passive pres of all technology types and see if there is any consensus towards LDRs. And in so doing move past this ridiculous idea that everything I post is nothing other than an agenda against NVA.

r100

27-06-2014, 16:21

precisely ! thank you for that ;-)

Marco

27-06-2014, 20:01

All this talk in some parts of the Internet about the supposed high distortion of LDRs, due to certain technical reasons and measurement pish, is nothing much more than another smokescreen, created by those with a commercial agenda.

When I listen tomorrow to some LDRs, at Jason's place, in comparison with my own current benchmark (the Croft), I'll be using *my ears* to judge what I hear, good or bad.

I couldn't give a tinker's cuss what the measurements say. I care more about the length and solidity of the last jobby which popped out of my bottom than (in most cases) sonically meaningless technical measurements.

As ever, in audio, the proof of the pudding is in the listening!!!

:exactly:

Marco.

rubber duck

27-06-2014, 20:04

Looking forward to your views Marco. Of the LDR, not your jobby...

Marco

27-06-2014, 20:13

Hehehe... No worries. Don't worry, all will be revealed in due course. As ever, I shall simply tell it as I hear it, and in the process be ruthlessly honest :)

I trust Anthony's judgement on these matters, and also know his system very well, so there's simply no way he would've heard what he's reported here with the LDR he's built if it wasn't inherently capable of producing excellent results, especially as I know how good the gear is he's comparing the LDR against!!

As such, I fully expect to be impressed with the LDRs I'll be listening to tomorrow. Whether or not one makes it into my system, however, is another matter entirely.

Marco.

P.S Snapper's down visiting, so he'll also be able to give his views on the matter.

Figlet108

27-06-2014, 23:55

Ok, the scene is set:

https://lh5.googleusercontent.com/-ivB_R8hmxsI/U64DV87n-uI/AAAAAAAADOE/p4xSu4ol7Lc/w906-h604-no/2014-06-28+00.18.29_resize.jpg

I've brought the NVA power amp down from the attic in place of the EAR 509s and Macca's Stereo Coffee is all set, as is the Tortuga.

My wife really likes the look of Macca's Stereo Coffee in its black acrylic simplicity, so Macca you may have to prise it off her... (good luck with that).

https://lh5.googleusercontent.com/-O0YLpMNcuCc/U64DV-Tj7jI/AAAAAAAADOA/clwWuvJ_cJs/w906-h604-no/2014-06-28+00.17.13_resize.jpg

Macca

28-06-2014, 07:03

Looking good!

Will see you later once the gas board has been and gone. What a pain in the ass they are.

Marco

28-06-2014, 08:38

Yup, looking good Jason... Just one thing, will we be able to get at the back of your power amp and/or speakers to reverse the polarity (positive and negative) of your speaker cables, in order to accommodate the signal phase-inverting of the Croft? :)

Marco.

Figlet108

28-06-2014, 08:49

Marco

28-06-2014, 09:02

Don't get me all excited, big boy! :bum:

Marco.

anthonyTD

28-06-2014, 09:19

I am looking forward to reading the opinions of all involved today,
As for my experimenting with the LDR, i haven’t really had much time to do any decent listening since i wrote my initial findings, so the verdict for me is still out on whether i think LDR's are in fact the be all and end all of passive attenuation, however, what i have heard to date in my system has been insightful, and impressive...
A...

Marco

29-06-2014, 12:37

For the results of what happened, see here: http://theartofsound.net/forum/showthread.php?33176-Pre-Amp-bake-off-What-Happened

Marco.

P.S I shall comment later this evening, as we have family and friends round for lunch :)

awkwardbydesign

01-07-2014, 07:56

Just got an email from Chris (LDR); the NIO says YES! :yay:

Marco

01-07-2014, 17:10

Sorry, who or what is NIO? :scratch:

Marco.

TortugaRanger

01-07-2014, 18:12

Sorry, who or what is NIO? :scratch:

Marco.

I believe the letter was from the UK NMO (National Measurement Office) which is the UK market surveillance authority responsible for enforcing the RoHS regulations with the UK.

This affirmative response, together with an earlier affirmative response from EU authorities on this same topic, makes it reasonably clear that products containing LDRs are acceptable under RoHS by virtue of the fact that there is currently no acceptable alternative material to cadmium sulfide in photoresistors.

The fact that a specific EU exemption for analog audio optocouplers (photoresisotrs) expired at the end of 2013 as a matter of course does not negate the application of this overarching policy which has now been affirmed by both the UK and EU authorities.

+1 for rational government policy.

Carry on.

Marco

01-07-2014, 18:16

Nice one, Morten, and thanks for the update! :thumbsup:

Marco.

awkwardbydesign

01-07-2014, 18:36

Chris thought they were called the National Instruments Office.

Barry

01-07-2014, 18:45

There are reports that magnesium chloride may become an acceptable, non-toxic substitute for cadmium sulphide/cadmium telluride in photovoltaic cells. This substitute may read across to LDRs.

Figlet108

01-07-2014, 19:42

I believe the letter was from the UK NMO (National Measurement Office) which is the UK market surveillance authority responsible for enforcing the RoHS regulations with the UK.

This affirmative response, together with an earlier affirmative response from EU authorities on this same topic, makes it reasonably clear that products containing LDRs are acceptable under RoHS by virtue of the fact that there is currently no acceptable alternative material to cadmium sulfide in photoresistors.

The fact that a specific EU exemption for analog audio optocouplers (photoresisotrs) expired at the end of 2013 as a matter of course does not negate the application of this overarching policy which has now been affirmed by both the UK and EU authorities.

+1 for rational government policy.

Carry on.

Great news Morten (and not altogether a surprising outcome - it was just a question of clarification).

I look forward to the next set of objections ;)

awkwardbydesign

01-07-2014, 19:44

I think that is to spray on solar panels to activate the cadmium telluride, instead of using cadmium sulphide. The sodium chloride, that is.

Barry

01-07-2014, 19:58

I think that is to spray on solar panels to activate the cadmium telluride, instead of using cadmium sulphide. The sodium chloride, that is.

It is definitely magnesium chloride, as the news item refered to it by name as well as saying it was a component of bath salts. If as you say, it only activates the cadmium telluride, then perhaps it is not a direct replacement for CdS in LDRs.

Looks like I was being premature in my statement!

NRG

02-07-2014, 03:22

I believe the letter was from the UK NMO (National Measurement Office) which is the UK market surveillance authority responsible for enforcing the RoHS regulations with the UK.

This affirmative response, together with an earlier affirmative response from EU authorities on this same topic, makes it reasonably clear that products containing LDRs are acceptable under RoHS by virtue of the fact that there is currently no acceptable alternative material to cadmium sulfide in photoresistors.

The fact that a specific EU exemption for analog audio optocouplers (photoresisotrs) expired at the end of 2013 as a matter of course does not negate the application of this overarching policy which has now been affirmed by both the UK and EU authorities.

+1 for rational government policy.

Carry on.

Not according to the reply I got from the EU just before I went on vacation! Quite the opposite. If I can gain access to my email I'll post the response, it does not look good.

awkwardbydesign

02-07-2014, 09:06

It is definitely magnesium chloride, as the news item refered to it by name as well as saying it was a component of bath salts. If as you say, it only activates the cadmium telluride, then perhaps it is not a direct replacement for CdS in LDRs.

Looks like I was being premature in my statement!
Sorry, magnesium chloride of course.

awkwardbydesign

02-07-2014, 09:06

Not according to the reply I got from the EU just before I went on vacation! Quite the opposite. If I can gain access to my email I'll post the response, it does not look good.

Ffs!

Marco

02-07-2014, 09:13

Lol, what a fooking joke... :mental:

All this to-ing and fro-ing with officialdom is a load of pedantic pish, especially for mere end users of LDRs. Fine, if you've got nothing else better to do with your time than write letters, and suffer from some form of neurosis, but for normal folks with a life, just do what you want/consider is right and get on with it!

That's exactly what I'll be doing, especially as there's so much conflicting information on the subject! :exactly:

Marco.

NRG

03-07-2014, 02:34

Unfortunately its not. For the end user to enjoy these products there are two companies here who want to legally sell into Europe, to do so they need to comply with all the EU bureaucracy. Crazy as it may be and as much as you or anybody can't give a toss about it all the two companies involved do. :ner:

I'll take it to PM with Chris and Mike if necessary as I know its getting on yer tits. ;)

anthonyTD

03-07-2014, 08:22

Hi Neal,
Please keep the discussions here, so that we can all know the outcome, it is frustrating, but as you quite rightly point out, they have to pass all avenues of legality!
Unfortunately its not. For the end user to enjoy these products there are two companies here who want to legally sell into Europe, to do so they need to comply with all the EU bureaucracy. Crazy as it may be and as much as you or anybody can't give a toss about it all the two companies involved do. :ner:

I'll take it to PM with Chris and Mike if necessary as I know its getting on yer tits. ;)

Marco

03-07-2014, 10:25

Yup, what's pissing me off is the continual contradictory statements emerging from one 'official' source or another. What we need is definitive and irrefutable proof (posted here as evidence), which outlines clearly and unambiguously that LDRs are either legal or illegal, instead of all this woolly flim-flam.

Then folks can decide what they want to do for themselves, instead of being fed a guilt trip by those with an agenda, posing as the 'goody two-shoes brigade'! ;)

Marco.

r100

03-07-2014, 11:03

´goody two-shoes brigade'! ;)

hilarious !

awkwardbydesign

03-07-2014, 14:51

I'm more the "We are the people our parents warned us about" brigade.
Anyway, I just want mine so I can get on with poisoning everyone.

Macca

03-07-2014, 15:38

I'm more the "We are the people our parents warned us about" brigade.
Anyway, I just want mine so I can get on with poisoning everyone.

Yes, I bought mine in order to take my revenge upon the world...
not really that arsed about the sound quality.

Marco

03-07-2014, 16:01

Makes a change, I guess, from having a 'voice-coil melter'.... ;)

Marco.

lurcher

03-07-2014, 22:50

which outlines clearly and unambiguously that LDRs are either legal or illegal

I am sure there is no question that LDR's as such are legal, Farnell sell the parts in question, clearly marked as non ROHS conforming. You are welcome and allowed to buy them and use them. What isnt allowed is to import or sell the completed units containing the parts in question. The makers of the preamps can definitely (from my reading) sell the completed units without the LDR's fitted and the LDR's them self for later fitting by the owner.

Gazjam

03-07-2014, 22:55

Legalese kills music, not home taping.

Barry

03-07-2014, 23:52

Gentlemen,

Throw-away remarks such as "goody two-shoes" and "voice-coil melter" are unhelpful, and do not add anything to the discussion on the SQ of LDR devices.

Marco

04-07-2014, 07:10

I am sure there is no question that LDR's as such are legal, Farnell sell the parts in question, clearly marked as non ROHS conforming. You are welcome and allowed to buy them and use them. What isnt allowed is to import or sell the completed units containing the parts in question. The makers of the preamps can definitely (from my reading) sell the completed units without the LDR's fitted and the LDR's them self for later fitting by the owner.

Hi Nick,

That is also my understanding of the situation. However, it would be useful to see this outlined somewhere, officially, in black and white in order to eliminate any confusion :)

Given that what you've written appears to be true, especially the bit I've highlighted, end users of LDRs can relax in the knowledge that what they're doing is NOT illegal. What's your view on LDRs 'drifting' in accuracy over time?

Marco.

lurcher

04-07-2014, 07:29

What's your view on LDRs 'drifting' in accuracy over time

I dont have one, I did build a LDR pre, but never had it long enough to measure or have any experience on long term behaviour.

But I would guess, its more a case of the parts not being run long enough before being matched. I would expect them to change more in the first 100 hours than the nest 100 days, but thats just surmise.

Marco

04-07-2014, 07:49

Ah, I see. Interesting... I believe that Paul Hynes has been using an LDR-based preamp for about five years without any problems, and I know how 'fussy' he is about equipment performing accurately and reliably ;)

In terms of my own situation, first of all I need to assess whether fitting an LDR into my Croft will result in a worthwhile sonic improvement (and the jury's still out on that one) before I get to judge whether or not its performance starts to drift.

If I discover that the latter is true, then the LDR will simply be removed and kept aside in my parts box as a 'failed experiment'.

Marco.

Light Dependant Resistor

04-07-2014, 10:10

Hi Marco
Data on longevity of LED's ( LDRs of course contain a LED ) , is approximately 25 years. Advice with any LDR preamp is to leave it at 1/4 volume when you are away. If used like this lifespan should be longer still. A LDR preamp I put together nearly 5 years ago, sounds equally as good today and measures the same.

Put into perspective, you would probably have changed your valves in the Croft pre , quite a number of times.

Cheers / Chris

Marco

04-07-2014, 10:14

Interesting, Chris. So essentially this 'drifting' nonsense is a load of exaggerated bollocks? ;)

Marco.

Light Dependant Resistor

04-07-2014, 10:40

Hi Marco
Yes, certainly with our circuit we do not see any drifting issues. Matching remains key though, once initially matched though they habit to stay that way.

Cheers / Chris

Paul Hynes

04-07-2014, 10:50

Hi Marco,

I have actually been using LDR volume control since 1995 and produced some custom build units over the following few years. These earlier designs were a little drifty as I was using them in a valve preamp and the LED drive current was provided via a potentiometer from a voltage source. Even so the sound quality was exceptional. Having to adjust the balance was accepted by myself, and my customers, as part of the price for the musical performance.

There are a few thermal drift mechanisms that need attention.

The first is the LED driving the LDR. The LED when conducting has a forward voltage drop that is temperature dependant and as the temperature changes this changing voltage drop, in series with the potentiometer and the voltage source, changes the ratio of voltage between the LED and the potentiometer. The potentiometer will also have a thermal drift and so will a simple voltage source and these will not track the LED drift as they are different mechanisms. The net effect is a changing current through the LED, which in turn alters the transmitted light level thus changing the LDR resistance. The solution for this is to provide a precision voltage controlled current source (VCCS) to drive the LED, and this current source is not affected significantly by the changing LED forward voltage drop so the light intensity remains much more stable.

The second drift condition is caused by the tempco of the LDRs themselves, and thermal coupling reduces their device to device thermal drift.

This is not the end of the story regarding drift, as the device to device matching is rarely close throughout the operating range. Also power supply noise and RFI breakthrough from mains driven supplies can be bothersome as they cause random fluctuations in light intensity in the LED. For this reason I use the same cascaded ultra low noise regulators I used in the SL1200 internal regulator upgrades to keep noise out of the way.

My current LDR volume control using the VCCS (voltage controlled current source) and reasonably matched devices has been operating for over five years without my having to adjust the balance control. This is the design I provided for a group buy on the DIY audio forum. The 65 steps between levels are approx 1 dB and the balance control is also adjusting by 1 dB increments, so if there are any device matching problems, they can be adjusted out to this precision which has proven adequate in a high resolution system. As stated I have not felt the need to use the balance control and no one in the household has complained about imbalance in the sound field. None of the group buy participants has yet complained to me of audible drift issues although several have failed to build the design correctly, but this is normal with DIY projects.

So, given that solutions to drift are possible there should be no reason to avoid using them in valve preamps although I cannot confirm that practically at present, because my line pre is passive, as I have no need of any voltage gain from my preamp or my power amp, and therefore have no valves in these positions.

Marco

04-07-2014, 11:20

Hi Paul,

Thanks for the info, and clarification with regard to how long you've been using LDRs.

There are a few thermal drift mechanisms that need attention.

The first is the LED driving the LDR. The LED when conducting has a forward voltage drop that is temperature dependant and as the temperature changes this changing voltage drop, in series with the potentiometer and the voltage source, changes the ratio of voltage between the LED and the potentiometer. The potentiometer will also have a thermal drift and so will a simple voltage source and these will not track the LED drift as they are different mechanisms. The net effect is a changing current through the LED, which in turn alters the transmitted light level thus changing the LDR resistance. The solution for this is to provide a precision voltage controlled current source (VCCS) to drive the LED, and this current source is not affected significantly by the changing LED forward voltage drop so the light intensity remains much more stable.

The second drift condition is caused by the tempco of the LDRs themselves, and thermal coupling reduces their device to device thermal drift.

This is not the end of the story regarding drift, as the device to device matching is rarely close throughout the operating range. Also power supply noise and RFI breakthrough from mains driven supplies can be bothersome as they cause random fluctuations in light intensity in the LED. For this reason I use the same cascaded ultra low noise regulators I used in the SL1200 internal regulator upgrades to keep noise out of the way.

That certainly explains what's going on, with regard to drifting - especially what you've outlined in the first paragraph (above).

My current LDR volume control using the VCCS (voltage controlled current source) and reasonably matched devices has been operating for over five years without my having to adjust the balance control. This is the design I provided for a group buy on the DIY audio forum. The 65 steps between levels are approx 1 dB and the balance control is also adjusting by 1 dB increments, so if there are any device matching problems, they can be adjusted out to this precision which has proven adequate in a high resolution system. As stated I have not felt the need to use the balance control and no one in the household has complained about imbalance in the sound field. None of the group buy participants has yet complained to me of audible drift issues although several have failed to build the design correctly, but this is normal with DIY projects.

I believe that you've discussed your LDR volume control with Anthony and were going to send him one to try? If so, would it be possible to incorporate it into the circuit of my Croft preamp? I believe that your LDR has the facility of remote control, which would also be handy! :)

Marco.