Building a new reference LDR pre amp

[Sovereign]

For about a month I've been brewing up ideas with Stereo Coffee in Australia. With my wacky ideas and their brilliant technical knowledge of a new LDR pre amp build. We have had what seems like daily emails for the last 3-4 weeks and the circuit boards should be complete tomorrow, ready for postage.
Meanwhile I've been pulling together a list of high quality components as I really want this pre amp to be a bit special and a somewhat of a reference.
At 11:30 least night I started putting the PSU together, very late to start I know but I wanted to get it underway.

as you can see it will be made up of two chassis, one for the LDR boards, input selector and volume pot etc and the other will be for the PSU which I started last night
http://i1138.photobucket.com/albums/n533/SovereignKing/IMG_1301.jpg (http://s1138.photobucket.com/user/SovereignKing/media/IMG_1301.jpg.html)

I have a bit of work to do tonight , then I'll try and finish off the PSU and test it
http://i1138.photobucket.com/albums/n533/SovereignKing/IMG_1300.jpg (http://s1138.photobucket.com/user/SovereignKing/media/IMG_1300.jpg.html)

[awkwardbydesign]

OK, I'll bite; why two PSUs? I only have one (as a battery charger) in mine.

[Sovereign]

It will be a dual mono pre amp ie. separate LDR board and PSU for each channel

[Puffin]

There is a "This Thread Is Useless Without Pictures" emoticon - we need one for "This Thread Is Useless Without Details" emoticon!

[Sovereign]

What details are you wanting Rob?

[Puffin]

All of them:D

Having built several LDR pre amps I am intrigued.

[awkwardbydesign]

Are the 2 mono boards the same as the stereo boards, but with only one set of LDRs? And if there are 2 control boards, how are you managing channel balance? When I can be bothered to make a new bigger case I want to go to remote control, I have an integrated amp with remote and I'm getting lazy!

[Old boy]

It will be a dual mono pre amp ie. separate LDR board and PSU for each channel

Following your thread with interest.

[Sovereign]

The format is a control board for the LDR's on what will become
2x mono board, and a control board for the h11f1m anodes.
Tests done last friday show having separate boards for each
set of anodes provides best audio performance.

[The Black Adder]

Looking great, James... When do you predict it to be finished?

[Sovereign]

Hi Jo

I think the LDR boards are being posted the the next day or so and will take 5 days to get to me.
I'll finish the PSU tonight so all I need to do it put together the pre amp. Maybe ten days or so...

[Sovereign]

The PSU is finished, a few days later then expected but there you go.
This would work wonders for your Tamp Brian.
Next up is the actual pre amp, I'll get going on that soonish.

http://i1138.photobucket.com/albums/n533/SovereignKing/IMG_2087.jpg (http://s1138.photobucket.com/user/SovereignKing/media/IMG_2087.jpg.html)
http://i1138.photobucket.com/albums/n533/SovereignKing/IMG_2088.jpg (http://s1138.photobucket.com/user/SovereignKing/media/IMG_2088.jpg.html)
http://i1138.photobucket.com/albums/n533/SovereignKing/IMG_2089.jpg (http://s1138.photobucket.com/user/SovereignKing/media/IMG_2089.jpg.html)

[Ali Tait]

Aye, it'll be alright when it's tidied up.. :-)

[Ali Tait]

Seriously, nice job mate. :-)

[brian2957]

Cheeky boy :lol:
One of these arrived at Brian2957 mansion the other day http://www.ebay.co.uk/itm/30W-DC12V-HiFi-Linear-power-supply-Regulated-PSU-for-DAC-headphone-amp-CL-215-/111544612626?pt=UK_Sound_Vision_Amplifier_Parts&hash=item19f893b712
One of the real gents on AOS is kindly checking it out for me and performing his magic on it . The verdict is pretty good BTW :thumbsup:
Dontcha just love this forum and its fantastic members :D

[Sovereign]

Aye, it'll be alright when it's tidied up.. :-)

Cheeky git !
I even put two fuses in it! Bet your proud of me :)

[Sovereign]

Cheeky boy :lol:
One of these arrived at Brian2957 mansion the other day http://www.ebay.co.uk/itm/30W-DC12V-HiFi-Linear-power-supply-Regulated-PSU-for-DAC-headphone-amp-CL-215-/111544612626?pt=UK_Sound_Vision_Amplifier_Parts&hash=item19f893b712
One of the real gents on AOS is kindly checking it out for me and performing his magic on it . The verdict is pretty good BTW :thumbsup:
Dontcha just love this forum and its fantastic members :D

£39!!! Thats incredible. The PSU I just made cost me £200, thats just for the raw parts, let a lone making a profit if I made it commercially.

[Ali Tait]

Cheeky git !
I even put two fuses in it! Bet your proud of me :)

:lol: safety first! :D

[Ali Tait]

Next thing will be seeing how it sounds with some fancy fuses.. :-)

[Sovereign]

Sod that! I would rather have no fuse at all!

[Firebottle]

Cheeky boy :lol:
One of these arrived at Brian2957 mansion the other day http://www.ebay.co.uk/itm/30W-DC12V-HiFi-Linear-power-supply-Regulated-PSU-for-DAC-headphone-amp-CL-215-/111544612626?pt=UK_Sound_Vision_Amplifier_Parts&hash=item19f893b712
One of the real gents on AOS is kindly checking it out for me and performing his magic on it . The verdict is pretty good BTW :thumbsup:
Dontcha just love this forum and its fantastic members :D

Be very interested in your thoughts/findings on this one Brian :)

Sorry for the thread drift .............

[awkwardbydesign]

Cheeky git !
I even put two fuses in it! Bet your proud of me :)
If my LDR pre is off with the power amp on (charging mode; not on purpose) there is a loud hum through the speakers. Just bear that in mind.


£39!!! Thats incredible. The PSU I just made cost me £200, thats just for the raw parts, let a lone making a profit if I made it commercially.
But is the PSU module as low noise as Lily's? Mind you, you could buy one (or 2) and replace those and it would still be cheaper!

[Sovereign]

I think both Lilly circuits were £23 together. I plan to give the Lilly board a good few months then swap it with the power supply boards that power my DDDAC as Stereo Coffee really liked the look of those.

[Sovereign]

I have pluged the new PSU into the loan Stereo Coffee LDR pre amp I have, I try to not look for things or read to much into my findings, but I could swear blind things sound better. I was already using a very good and well regarded PSU for the LDR pre, the one that I use for my DDDAC, but this one seems to have the edge, and hopefully it only improves.

[Sovereign]

The eagle has landed, now I just have to find the time to wire it all up.
http://i1138.photobucket.com/albums/n533/SovereignKing/image.jpg1_1.jpg (http://s1138.photobucket.com/user/SovereignKing/media/image.jpg1_1.jpg.html)

[The Black Adder]

Ooooh!... Saucy!... :)

[aleman]

Hello iam building something similar to what you have built .having got two mono boards from stereo coffe .Can you please tell me where you purchased the transformers that you are using as I aim hoping to build a the same power supply for my boards .thanks a lot Aleman.

[Sovereign]

Sorry I never did update this thread, I got carried away with another project.
Here is a picture of the finished psu . I got the rcore transformers from eBay, I'll have to find you a link. The trannies are massively bigger then they need to be, I think 80va in the end ;-)
http://i1138.photobucket.com/albums/n533/SovereignKing/IMG_2087.jpg (http://s1138.photobucket.com/user/SovereignKing/media/IMG_2087.jpg.html)

[The Black Adder]

very nicely done, Shane. :) - I did wonder the other day how it was going :)

[Sovereign]

Here you go Alrick
http://www.ebay.co.uk/itm/230V-80W-12V-X2-OUTPUT-R-CORE-TRANSFORMER-With-SHIELDING-FOR-AUDIO-/321465862187?ssPageName=ADME:L:OC:GB:3160
Shout if you have any questions

[awkwardbydesign]

When it's newly charged my battery gives 12.7 volts, and I use it down to 12 volts. I swear it sounds better around 12.3 volts. But don't ask me to prove it!
So it may be worth experimenting with the power supply voltage.

[Sovereign]

Thanks Richard

[aleman]

Thanks James for the quick reply just a few questions, where did you get your cases from as well as the output sockets ,also what rating for the fuses will you be using .Thanks a lot Alrick.

[Sovereign]

Hi Alrick
The fuses are 3A I tried to use smaller ones recommended to me but they kept on blowing, maybe due to the transformers being larger than needed.
The connectors are just spare ones I had lying around rated at 20A obviously smaller ones could be used http://distributionzone.com/store/neutrik/product-powercon-true-1-mains-chassis-duplex-cbc-nac3px-neutrik-conac3px-1053/
I'm trying to find a link to the cases I have, I used one for the psu and a separate one for the LDR boards, let me get back to you.

[awkwardbydesign]

I bought a small PSU case from these people. As it was in their UK warehouse it was cheap.
http://stores.ebay.co.uk/doukmall/UK-Warehouse-/_i.html?_fsub=10239696010&_sid=1218230050&_trksid=p4634.c0.m322

[aleman]

Thanks for the info Jame si will get onto this once I haver returned from the annual trip to the seaside.cheers Alrick.

[awkwardbydesign]

James, I don't know if Chris has sent you new control boards to try, but I have had 4 up to now. Mk2 sounded better than Mk1, Mk3 sounded harsh, so I am back with Mk2. I haven't tried Mk4, after discussing it with Rupert (r100). He received 2 new boards, and it seems the Mk4 sounded worse than the Mk2 (if that is what he has). I must email Chris and ask him.
I don't know why the control boards make such a difference, as they are simply(?) setting the voltage for the LDRs. The harsh sounding board seemed to have a lot of zener diodes, perhaps that is the reason?
At the moment I am fiddling with the speakers (still!), and making cables, so haven't focussed on the LDR pre. But I will try running the battery voltage down to 11.9v (12.3 at the mo) and see if I can hear differences with the same pieces of music. Even I can conduct that experiment! I'll let you know if I hear anything.

[Sovereign]

Hi Richard

Chris did say there is a updated board to send to me, I haven't had a chance yet as work is relentless at the moment.
I received my LDR boards maybe 6 months ago, so I don't know if that makes them Mk 1,2,3 or 4.
All sounds very good this end and not a harsh tone in sight.

[Desmo]

Is there any way of telling which release of control boards I have - are they marked in some way? I still have the original boards that Chris sent me in August last year, I did not know about any others being available. They sound just fine to me, but I'd be interested in knowing what version they are.

[awkwardbydesign]

Is there any way of telling which release of control boards I have - are they marked in some way? I still have the original boards that Chris sent me in August last year, I did not know about any others being available. They sound just fine to me, but I'd be interested in knowing what version they are.

It's confusing, it probably depends where you joined the sequence. I had photos of r100's boards, but I may have deleted them. The latest version we had came with brass pillars mounted on them, but they all look so similar it's hard to differentiate them. I'll have to ask Chris to tag them!

[Sovereign]

Maybe email Chris, or maybe Chris can comment on this thread?

[Sovereign]

I just emailed Chris just now and asked him to comment on this thread, he is in another time zone so it may be late tonight.

[awkwardbydesign]

I PMed him too! But he is 11 hours different. So he should be up soon.

[Light Dependant Resistor]

I just emailed Chris just now and asked him to comment on this thread, he is in another time zone so it may be late tonight.


Thanks James and Richard, Yes very early morning here I think the thread is asking
for a history and direction with the many changes to boards that has occurred,
so I will do my best to reply

LDR's have a anode positive and cathode ground. The most common circuit
form is what is called an L pad being a series which is an LDR in series
between the input and the output and a shunt LDR between the output and
ground.

The hallmark of a good circuit is one that enables no audio volume when off,
and enables excellent audio. Other designs concentrate on stressing the LDR
to try to make the shunt lower and lower in resistance to make the audio volume
be off, using up to 22ma per LDR beyond its recommended range.

I recall a conversation with David at Audio Synthesis where they tried LDRs
but similarly could not get the circuit to turn off. The specifications state
R onfor the NSL32SR2S as being 40 ohms at 16ma.

Why all this fuss over volume being off ? Well it makes your enjoyment of audio
just a bit better if you can lower the volume sufficiently and have it mimic a
conventional potentiometer that turns off.

Every board we have done has always had the ability to turn off whilst delivering
no more than 8 ma to each LDR, this is because there is no resistance directly in
parallel with the LDR, and it is far more sensible to make the series resistance
extremely high which enables then contactless switching of inputs and ability
to have as many inputs as are required.

This design arose as a delivery of potentiometers as singles rather than dual
gangs, where I set about designing boards to use a single gang and not involve
ground, rather allow the cathode of the LDR to be the grounding point.

As it happens there is more to this, if you look at designs Silonex did, they always
had a diode in the anode line, and up to two diodes in the cathode line, so that
the photodiode or LED in the LDR was always in a semiconductor space -one
or two junctions away from other capacitance and resistance for instance in
power supplies.

There have been a number of control boards, and abilty for updates if and when required.

The earliest boards used a diode inward to a 7805 regulator arranged as a
current Vref /R circuit, that is the ground of the regulator was the circuit point
sensing and delivering current from the regulators output via a combination of
set and active resistance. There were yes boards with zener diodes which were
not as good sounding, although voltage was nicely low and boards now
that use a secondary current source. Changes were made also to the LDR
boards to have trims to precisely set Left Right balance.

Although I have scopes and meters, most setting of boards is done with
listening via ESL57's and Quad 306 power amps,

Cheers / Chris

[Light Dependant Resistor]

I just emailed Chris just now and asked him to comment on this thread, he is in another time zone so it may be late tonight.


Sorry double post
Cheers / Chris

[Sovereign]

Thanks for your response Chris, I understand some of it :)
And thanks again for your patience when I was building my amp

[awkwardbydesign]

I've spoken to Chris again, and asked a couple of questions. I guess he will probably come back here with some more info when he's ready.
I am still trying to hear if there are differences in the sound as the battery voltage drops, but I can only do it once a day as the battery holds it's voltage so well! There seems to be an improvement as it drops from 12.7v (full charge) down to 12.3v, but below that it is hard to tell. As soon as the power amp warms up I will be listening at 11.8v. There is a limit to how low I can go, as the battery won't like it.
If there is a real difference, perhaps it is due to the regulator having to dissipate too much voltage. It's only a 7805, I believe, so it's losing about 7 volts as heat.
It's easy to try, I don't even have to move, just wait! :) I'll let you know what I think, but I wonder if a different regulator would make any difference. I don't know enough to answer my own question.

[struth]

i was looking at a ldr kit for a passive pre on ebay...i wonder if its one of yours chris...sure it was from the Antipodes ....if it was was wondering if its easy to do

[awkwardbydesign]

i was looking at a ldr kit for a passive pre on ebay...i wonder if its one of yours chris...sure it was from the Antipodes ....if it was was wondering if its easy to do
If it's the Stereo Coffee then yes, it's Chris's. I find it easy enough to work with, the boards are ready made, you just add a PSU of your choice (battery for me) and put it in a case. I have two boards to get 4 inputs (up to 3 inputs per board), one control board and whatever extra controls you want. I added a simple overall balance control. Put it in a case and Bob's your uncle. Or you can go mad like James!
It's hard to see how you could better the sound anywhere near the price, just make sure your power amp's input impedance is 47k or more, and you don't need any gain (I don't) and you can't go too far wrong.

[Desmo]

If it's the Stereo Coffee then yes, it's Chris's. I find it easy enough to work with, the boards are ready made, you just add a PSU of your choice (battery for me) and put it in a case. I have two boards to get 4 inputs (up to 3 inputs per board), one control board and whatever extra controls you want. I added a simple overall balance control. Put it in a case and Bob's your uncle. Or you can go mad like James!
It's hard to see how you could better the sound anywhere near the price, just make sure your power amp's input impedance is 47k or more, and you don't need any gain (I don't) and you can't go too far wrong.

+1

I built a 6 input version, with 2 control boards into an existing pre-amp chassis, and it was a fairly easy build. You do need to plan though, and determine how much if any soldering you are prepared to do - there is no need to do any soldering if you don't want, but I wanted to use my own sockets etc and am happy with a soldering iron. Also you need to think about the power supply - but Chris will happily guide you through the process, and he supplies some useful instructons.

[awkwardbydesign]

+1

I built a 6 input version, with 2 control boards into an existing pre-amp chassis, and it was a fairly easy build. You do need to plan though, and determine how much if any soldering you are prepared to do - there is no need to do any soldering if you don't want, but I wanted to use my own sockets etc and am happy with a soldering iron. Also you need to think about the power supply - but Chris will happily guide you through the process, and he supplies some useful instructons.
You might need to solder the volume control and selector switch, but basically almost none. And if you buy a case with cutouts for an IEC socket and RCAs, very litle drilling. Just a few holes to mount the boards. I have been looking at something bigger like this, so I can add a remote controlled volume and selector switching unit, but I'm too mean. I'll probably build something eventually.http://www.ebay.co.uk/itm/Rounded-aluminum-chassis-amplifier-case-silver-enclosure-DIY-house-356X84X316mm/271648102682?_trksid=p2060778.c100276.m3476&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%2 6asc%3D20140725133651%26meid%3Dc2a967c13e7d4cc1bdf 84711be985340%26pid%3D100276%26rk%3D1%26rkt%3D4%26 mehot%3Dlo%26sd%3D261686249238
http://i.ebayimg.com/00/s/NTc1WDU3MQ==/z/518AAOSwPYZU7lBI/$_35.JPG

[awkwardbydesign]

Well, I've tried 11.8v and can't hear any improvement. I won't go lower for the sake of the battery, but it's really hard to listen critically when the sun is streaming in through the window. Just too distracting, and seems somehow wrong! Like coming out of the cinema and finding it's daylight. Which since we have retired we do quite a lot. It's weird!
12.3v seems nice, but I could be imagining the whole thing, so I'll let someone else take it further if they want to.
I'm off to compare cables now. :doh:

[struth]

It was this one .. Light Dependant Resistor 3 input Preamp Kit. 3 would do me nicely. No probs doing soldering although my eyes are getting poor and hands a bit shakey Jake lol. gettin' old ya know.

Might be a nice project. hmm

Thanks for the replies all :)

[Sovereign]

If it's the Stereo Coffee then yes, it's Chris's. I find it easy enough to work with, the boards are ready made, you just add a PSU of your choice (battery for me) and put it in a case. I have two boards to get 4 inputs (up to 3 inputs per board), one control board and whatever extra controls you want. I added a simple overall balance control. Put it in a case and Bob's your uncle. Or you can go mad like James!
It's hard to see how you could better the sound anywhere near the price, just make sure your power amp's input impedance is 47k or more, and you don't need any gain (I don't) and you can't go too far wrong.

Interesting what you say about needing an input impudence of anything more than 47k as my class A is only 22k, I'm making a new class A power amp so this can be adjusted.
Saying that, if my current amp has an input impudence of 22k does that mean that things would sound better with a Hightower input impedance than 22k?
Thanks

[awkwardbydesign]

Interesting what you say about needing an input impudence of anything more than 47k as my class A is only 22k, I'm making a new class A power amp so this can be adjusted.
Saying that, if my current amp has an input impudence of 22k does that mean that things would sound better with a Hightower input impedance than 22k?
Thanks

You need to ask Chris about this. But he says he uses a Quad 306 for most evaluation, and I just googled the specs http://www.hifiengine.com/manual_library/quad/306.shtml which say the input impedance is 20k. So I may be overcautious. It's just that normally a high input impedance would mean less chance of a mismatch. The Tortuga site gives a graph of their LDR pre's output impedance (Chris's may be different, my memory is unreliable these days), which rises from 100ohms up to about 5 or 6k. Ideally the following input impedance should be much higher, maybe 10 times. But if Chris's works into 20k then you'll be fine. I like to aim for 100k (valves are generally this high) for best dynamics. But as I say, Chris is the expert here, it's certainly not me!

[Sovereign]

Thanks Richard

[struth]

I think my Wad power should be 47k. sure thats the pot on the integrated version and tmk they are the same apart from the pot and switch. Have to give it some thought
I know you were not talking to me but thanks for the info anyways.

[awkwardbydesign]

I'll talk to (almost) anyone. I talk to myself if no-one else will listen.

[brian2957]

Hah ! I can sometimes start an argument with myself if there's no one else around Richard :lol:

[Light Dependant Resistor]

i was looking at a ldr kit for a passive pre on ebay...i wonder if its one of yours chris...sure it was from the Antipodes ....if it was was wondering if its easy to do

Hi Grant
Yes easy to put together, there are lots of diagrams and images, and I am here 24/7 giving help.
LDR's are a passive - although some would infer from the audio they provide, akin to a active pre amp

I have yet to find a combination of equipment that failed to impress, or work exactly as required
Yes Richard is right I use a Quad 306 that has a 22k input impedance

The advice I can give is use a source component with ability to drive into a 600 ohm
load - thats about 99% of everything available as most will now do as low as 100 ohms
or better, particularly modern DAC's . and a power amp with input impedance above 20k,
and sensitivity of 800 mv or less, which thankfully also is the majority of power amps,

The old days of insensitive equipment and specific source components are thankfully long gone,
LDR's being capable of being a top choice of attenuation to preserve audio at the preamplifier
analog line level , and at the same time getting along well with other equipment.

Cheers / Chris

[struth]

Hi Grant
Yes easy to put together, there are lots of diagrams and images, and I am here 24/7 giving help.
LDR's are a passive - although some would infer from the audio they provide, akin to a active pre amp

I have yet to find a combination of equipment that failed to impress, or work exactly as required
Yes Richard is right I use a Quad 306 that has a 22k input impedance

The advice I can give is use a source component with ability to drive into a 600 ohm
load - thats about 99% of everything available as most will now do as low as 100 ohms
or better, particularly modern DAC's . and a power amp with input impedance above 20k,
and sensitivity of 800 mv or less, which thankfully also is the majority of power amps,

The old days of insensitive equipment and specific source components are thankfully long gone,
LDR's being capable of being a top choice of attenuation to preserve audio at the preamplifier
analog line level , and at the same time getting along well with other equipment.

Cheers / Chris

Thanks Chris. is ebay the best place to buy one fir you?

[Light Dependant Resistor]

Thanks Chris. is ebay the best place to buy one fir you?

Yes, Thanks Grant

[Sovereign]

I hath to commend Chris on his incredible patience. I had a few problems that was only due to my severe lack of intelligence. Chris guided me through on Skype

[Sovereign]

Well maybe a year later, my LDR pre amp is finally finished! I was somewhat distracted by making my Wonfor monster Class A power amp in the middle of my LDR build. So here are a few snap shots of the finished build. In this time Chris at Stereo Coffee had a new LDR board for me to fit, as I was having a few teething problems I packed up just the LDR side of the amp and posted it to him in New Zealand, well while my amp was there he used it to try a few modifications on, and in doing so he has completely re built the whole amp, so a BIG hats off to Stereo Coffee for their Stirling service! I'm pretty sure my LDR is one of a kind, especially as I have a dual power supply and dual mono LDR amp.
The real qualities about this amp is the speed of the music and the timing is as quick as a certain Jamaican sprinter. The musical presentation is wider and musician / singer placement and transparancy is exceptional, I most definitely feel closer to the music. There is more detail coming through for sure, I love hearing all the timing nuances of David Brubeck on the piano, and musical inflections I had no idea were there. I have never heard so much detail, such a wide musical presentation with pin point musician placement with enough drive and grunt for my power amp to lap up.
seriously though Well done Chris at Stereo Coffee.
http://i1138.photobucket.com/albums/n533/SovereignKing/image.jpeg (http://s1138.photobucket.com/user/SovereignKing/media/image.jpeg.html)
http://i1138.photobucket.com/albums/n533/SovereignKing/image_1.jpeg (http://s1138.photobucket.com/user/SovereignKing/media/image_1.jpeg.html)
http://i1138.photobucket.com/albums/n533/SovereignKing/image_2.jpeg (http://s1138.photobucket.com/user/SovereignKing/media/image_2.jpeg.html)
http://i1138.photobucket.com/albums/n533/SovereignKing/image_3.jpeg (http://s1138.photobucket.com/user/SovereignKing/media/image_3.jpeg.html)

[Ali Tait]

Looking good mate, glad it's doing the business for you.