Dual mono passive Pre amp, single ended (advice) [Archive]

macvisual

26-12-2016, 21:06

RothwellAudio

27-12-2016, 09:11

All passive pre amps are dual mono. "Dual mono" is a term usually applied to stereo amps that have independent left/right power supplies, but passive pre-amps don't have power supplies anyway.

farflungstar

27-12-2016, 09:30

There are better passives than the Promitheus and for sound electrical reasons, autoformers are better and the best are the Dave Slagle autoformers. Two separate modules constitute right and left so definately dual mono.

With any luck I will have a beautiful example of one up for sale shortly but if you decide to go your own route the modules are only around 350$ - and incredibly simple to set up. Lol if I did it anyone can - they're almost plug and play.
Adey

Sent from my Aquaris E4.5 using Tapatalk

Sovereign

27-12-2016, 10:57

Here is internal shots of my dual mono Stereo Cofee passive pre.
It certainly is dual mono as the left and right channels are totally separate. This is a heavily modified one by Chris Daly. I carried out the build but I got a bit stuck, Chris very kindly finished it off and used it as a bench model to carry out some new work. I've always been thoroughly impressed with it, and it has been up against some stiffy competition.

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.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)

Arkless Electronics

28-12-2016, 14:09

IMO the best possible way to make a passive is to use a switched attenuator. The units from Khozmo are very good and he supplies complete passive pres or just the switched attenuators. I would take such a passive pre over any unit involving any other techniques such as switched auto transformers or LDRs.
The latter two have their followers but IMHO the colourations and distortion they add in comparison to a straight attenuator are themselves the reason some prefer them..... I like my fidelity as high as possible :)

RothwellAudio

28-12-2016, 15:33

IMO the best possible way to make a passive is to use a switched attenuator... I would take such a passive pre over any unit involving any other techniques such as switched auto transformers or LDRs.
Yes, I agree. I think the main attraction of the "alternative" approaches is that they're different, they're unusual and therefore they aren't mainstream - that makes them very appealing to those who believe audio nirvana lies well off the beaten track and must be sought via esoteric means. However, I believe that sometimes the simple solution is the best.

Sovereign

28-12-2016, 16:06

Yes, I agree. I think the main attraction of the "alternative" approaches is that they're different, they're unusual and therefore they aren't mainstream - that makes them very appealing to those who believe audio nirvana lies well off the beaten track and must be sought via esoteric means. However, I believe that sometimes the simple solution is the best.
I can't agree with you Andrew, I wasn't appealed to LDR as it's 'off the beaten track' or whatever you were on about. When several pre amps were compared, the LDR sounded better to me plain and simple. I wasn't looking for something 'different or unusual' it was merely a simple case of amp comparisons. I not an easily led numpty banana :carrot:, where is a banana emoticon when you want one .

British high fidelity

28-12-2016, 16:45

[emoji529]

Sent from my LG-H961N using Tapatalk

British high fidelity

28-12-2016, 16:55

Having just had a 4 input LDR pre made by Chris i can agree with soverign,

The sound of LDRs is very very good, I have had the famous krell KRC and many other SS pre’s and also just moved on from the Prometheus TVC, and it for me is the search for unclouded, uncoloured pure high fidelity sound

Isnt pure Hifi sound our goal, reproducing that live or studio recording in our living rooms

Cheers

Sent from my LG-H961N using Tapatalk

macvisual

28-12-2016, 17:21

Sorry, what does LDR mean...?

British High Fidelity, how did you find listening/auditioning the Promitheus Audio TVC pre-amp...? What would better it do you think..?

Regards;
Peter

Arkless Electronics

28-12-2016, 17:29

wee tee cee

28-12-2016, 17:35

Peter,
I have a promethius TVC pre. My son runs it with temple mono blocks.
I have a BTE and Tisbury audio passive to compare it with. Ive run a Beresford Capella and MF HPA as active pres in the past.

Nothing too exotic but all good in theyre own right. The promethious is the least coloured and neutral that I have tried. Doesnt seem to bring any nasties to the sound-sounds more dynamic than the other passives and less overblown and artificial than the actives ive tried.

Just my tuppence worth-your mileage may vary.

I found it worked well with class d/tube amps rather well.

Arkless Electronics

28-12-2016, 17:37

Sorry, what does LDR mean...?

British High Fidelity, how did you find listening/auditioning the Promitheus Audio TVC pre-amp...? What would better it do you think..?

Regards;
Peter

Light Dependent Resistor. A few passives use the "out there" method of changing the amount of light being shone on LDR's to turn volume up and down. This produces easily measurable distortion and therefore any perceived "better than a switched attenuator" sound quality is due to it "messing with" the original signal.

Some take the attitude of "hey I don't care how distorted or coloured it is. I like what I hear".... Personally I want the truth, the whole truth and nothing but the truth. YMMV

British high fidelity

28-12-2016, 17:59

Sorry, what does LDR mean...?

British High Fidelity, how did you find listening/auditioning the Promitheus Audio TVC pre-amp...? What would better it do you think..?

Regards;
Peter
Hi brother, LDR = (Light dependant resistor) you can google the details for more explanation as its quite difficult to explain lol well is for me

Dont get me wrong the Prometheus is absolutely amazing - seriously, the clarity is superb and the soundstage truly great, i have lived with mine for 3 years and it still brings a smile to my face all the time

One amazing thing about passive pre’s is the blackness, this is the parts of recordings when the music stops or pauses with no sound from the artist or musicians with SS (Solid state) amps there is always a low level hiss or noise its hard to describe, but with passives there is nothing no sound whatsoever

This blackness is amazing its as it would be in a live recording, Solid state and valve pre’s always have low level noise in the recording this apparently is due to the electrical signal being run through the circuit (I think)!

So i hear you ask why have you upgraded from the Prometheus if its so good,

The LDR Pre takes everything the Prometheus has and just does it so so so so much better, the first time i heard it was after Chris Daly known as light dependant resistor on this forum loaned me his LDR pre

I played Dire Straits on every street on vinyl this is a track i know very very well and is my test track and all i can say is Wow, the soundstage was phenomenal i honestly thought my listening room had quadrupled in size, the timbre of the instruments and the seperation of the instruments was breathtaking

I was sold after just 2 mins of listening its that good

All i can say is that hearing this pre amp was a moment in my audiophile journey that litrally took my breath away and i still have huge smiles everytime i listen to it

I hope this helps

Cheers

Sent from my LG-H961N using Tapatalk

British high fidelity

28-12-2016, 18:02

Light Dependent Resistor. A few passives use the "out there" method of changing the amount of light being shone on LDR's to turn volume up and down. This produces easily measurable distortion and therefore any perceived "better than a switched attenuator" sound quality is due to it "messing with" the original signal.

Some take the attitude of "hey I don't care how distorted or coloured it is. I like what I hear".... Personally I want the truth, the whole truth and nothing but the truth. YMMV
Some people disagree and all i can say is http://uploads.tapatalk-cdn.com/20161228/5651092b13deee0063f788b77c46cb3b.jpg

Sent from my LG-H961N using Tapatalk

Arkless Electronics

28-12-2016, 18:44

Some people disagree and all i can say is http://uploads.tapatalk-cdn.com/20161228/5651092b13deee0063f788b77c46cb3b.jpg

Sent from my LG-H961N using Tapatalk

Some in the realm of hi fi not only can't handle it but don't want it..... Personally I like my fidelity high... but not "enhanced" ;)

danilo

28-12-2016, 18:59

I quite like the idea of a Dual Mono passive preamp (single ended), many years ago I owned one by Audio Synthesis, but quite fancy returning to this simple single input again...

I know there's many models/designs out there I'm looking at the Promitheus Audio version...

Are there any benefits of the Dual Mono passive pre's (single ended) compared to the normal passive setup I wonder..?

Regards;
Peter
Scotland

I replaced a 10 years owned bespoke George Wright Tube pre.. with a simple stupid Dact clone 10k stepped pot, a bit of Cat 5 wire, fitted in a tiny 2$ wooden box from a local 1$ shop.
A day vs night improvement. Tube was good by most yardsticks. The cobble up was simply better. I was gobsmacked.
Silence ?? Ears pressed close to my Tannoys' dustcaps .. Volume in any position and there is ..Nothing at all .. Total dead silence.
First time I tried this I had to go and check to see if the wall plugs were in.
Clearly KISS has merit.
Next step (when I get 'roundtoit) will be to add a second identical pot so that each pot operates only one channel.
A defacto balance control. In case I ever feel the need for such.

macvisual

28-12-2016, 19:19

Light Dependant Resistor

28-12-2016, 19:25

Light Dependent Resistor. A few passives use the "out there" method of changing the amount of light being shone on LDR's to turn volume up and down.

The attached diagram shows how an audio purpose LDR functions 18950
On one side a LED, on the other a variable resistor, in between - nothing other than light.
With respect to audio signals - replacing mechanical interfaces invented by Mary Hallock- Greenewalt
as the rheostat in 1919, ironically to turn a lamp on.
https://www.google.com/patents/US1357773?printsec=abstract&dq=mary+hallock-greenewalt&ei=IOeoUcaYLJStrgG70oHQDg#v=onepage&q&f=false

British high fidelity

28-12-2016, 19:34

Great replies, thanks, keep them coming guys n' gals!

So which exact model is your LDR pre can I ask..?

I've just bought a pair of minty/used World Audio Design 300B valve mono-blocks, push/pull design, (they arrive sometime in January), Audioplan Kontrast MkII floorstanding speakers, Kinshaw Perception 2x box switchable MM/MC phono-stage, Acoustic Signature Challenger MkI turntable/SME V/Len Gregory Music Maker 3 moving iron cartridge etc...

Thanks;
Peter
Hi brother your welcome and im happy to help, there are no model numbers, you can contact Chris (Light dependant resistor) i see he has just posted in this thread

Basically you tell him what you want and he builds it, Chris is amazing to work with i dont think he ever actully sleeps lol, he responds very quickly to questions and advises on ideas you may have

Send him a PM if your interested

Cheers

Sent from my LG-H961N using Tapatalk

Infinitely Baffled

29-12-2016, 08:19

Deep breath, chaps! I 'm about to demonstrate my ignorance.

This is a thread about passive pre-amps, right? Yet, in the photographs contained in posting #4, the cases are stuffed with components. I thought the whole point about a passive pre-amp was that it didn't employ all the gubbins that go into an active. Certainly, I have built one or two in the past that consisted only of "in" and "out" sockets, a source switch, a potentiometer and some wire. Sounded great to me (quite possibly down to my sense of amazement that it worked at all). So what is the rest of the innards in post #4? Is it all circuitry required to support the LDR technology, or have I totally missed the point about passives?
Cheers. IB.

British high fidelity

29-12-2016, 08:43

Lol i will let Chris answer that as its over my head

Sent from my LG-H961N using Tapatalk

Light Dependant Resistor

29-12-2016, 08:51

LDrs are as simple as it can get on their signal side, hence you see just connection
to and from the RCa sockets. But on their anode and cathode a different story.

Ideally the anode and cathode relationship is a potential difference, not necessarily directly
grounding the cathode, Some versions of LDr circuits mix signal ground with DC ground
the better ones do everything to avoid this.

Cheers / Chris

RothwellAudio

29-12-2016, 10:06

I can't agree with you Andrew, I wasn't appealed to LDR as it's 'off the beaten track' or whatever you were on about. When several pre amps were compared, the LDR sounded better to me plain and simple. I wasn't looking for something 'different or unusual' it was merely a simple case of amp comparisons. I not an easily led numpty banana :carrot:, where is a banana emoticon when you want one .

No offence intended, and I certainly don't think you're an easily led numpty banana. If you tried out several different pre-amps and you chose the one with the LDR volume control I don't doubt that it was better than the others. However, I do doubt that the LDR volume control was the reason for its superiority.

Light Dependant Resistor

29-12-2016, 10:20

No offence intended, and I certainly don't think you're an easily led numpty banana. If you tried out several different pre-amps and you chose the one with the LDR volume control I don't doubt that it was better than the others. However, I do doubt that the LDR volume control was the reason for its superiority.

Cryptic ? How can an LDR be anything other than an LDR ?
Perhaps you mean removing the mechanical wiping and grinding of conventional pots,
and ridding circuits of signal side input switching, all good reasons why.

walpurgis

29-12-2016, 10:22

struth

29-12-2016, 10:28

Thought the tvc i had was very good too. It didnt work well on every set up i tried it on, but most. I am not big on passives tbh in general, and best pres overall ive used bar the tvc have been good actives.

Clive

29-12-2016, 10:37

Passives need to be treated with a little bit of care, eg:

- for a potentiometer or switched attenuator the value chosen can influence the tonal balance and well as there being possible interactions with valve phono stages

- if you use a volume control in shunt configuration the value of the shunt resistor will often significantly change tonal balance

- the cables on the output to the power amp can be an issue as can driving modern solidstate power amps and line level subs - which surprisingly often have a 20k input impedance - power and amp sub amp both with a 20k input impedance is bad news.

- TVCs and AVCs suffer some of these issues too

I find TVCs and AVCs to be very neutral sounding and they sound better than plain resistive attenuators at low volumes - this is sometimes put down to transformers preserving current and only attenuating voltage, is this technically correct?

Overall I'd say passives are less likely than active preamps to be an instant ideal match for any particular power amp. Many integrated amps use a passive (simple pot), in this case the manufacturer is able to select the ideal value pot for the amp and the internal cables are very short, so this is a good environment for a passive volume control.

I'm very much in favour of my AVC pre. That said I feel many people want their systems to have a little personality or be tonally matched to their room, this IMO is best done in one place in the system, either with the speakers or preamp. Ear-bleeding high fidelity doesn't suit everyone so a preamp (likely to be active) can be useful in some systems not just for gain purposes but also for adding that "personality".

Just some of my musings......

Macca

29-12-2016, 10:42

It has been implied that TVC, autotransformer and LDR pre-amps contribute artifacts and distortion. But, users report an improvement or better sound than via active and basic passive pre-amps. Why is this?

Since using a TVC device, I'm convinced that the sound is better than any pre-amp I've tried before, whether pot-passive, stepped attenuator or active type (valve or solid state).

To suggest that the perceived benefits are the result of 'pleasant sounding corruptions' of the signal seems wrong, as I hear greater clarity, neutrality and purity than before. I have not yet tried an LDR unit, but guess users are having similar experiences.

There has to be more to this. I'm thinking that regardless of measurable artifacts and distortions, the three types of pre-amplification in question offer capabilities that have not yet been quantified properly and that those who rely solely on measurements to judge them are missing something.

I've heard several auto-transformer designs and LDR designs in comparison and none of them sounded identical so I don't think broad comparsions of the sound of these different approaches actually works in practice. Certainly not to the point where you could say that one particular topology was superior. My own opinion is that a quality stepped attenuator sounds the most natural as much as that can be quantified, however there is very little in it.

I have only heard two active pre-amps that I thought were on a par with a good passive (of any type) and they are Marco's modded Croft and Barry's Mark Levinson. Both ruinously expensive bits of kit.

Light Dependant Resistor

29-12-2016, 10:42

It has been implied that TVC, autotransformer and LDR pre-amps contribute artifacts and distortion. But, users report an improvement or better sound than via active and basic passive pre-amps. Why is this?

Since using a TVC device, I'm convinced that the sound is better than any pre-amp I've tried before, whether pot-passive, stepped attenuator or active type (valve or solid state).

To suggest that the perceived benefits are the result of 'pleasant sounding corruptions' of the signal seems wrong, as I hear greater clarity, neutrality and purity than before. I have not yet tried an LDR unit, but guess users are having similar experiences.

There has to be more to this. I'm thinking that regardless of measurable artifacts and distortions, the three types of pre-amplifier in question offer capabilities that have not yet been quantified properly and that those who rely solely on measurements to judge them are missing something.

James, Sovereign presently has the LDr loaner unit which I built many years ago. I will arrange with James for its return here to New Zealand- to update its boards, then provide it back so
each one of you can hear what we are hearing - does that sound like a good idea ?

walpurgis

29-12-2016, 10:45

This is all rather like the debate in the late sixties/early seventies, over which was best. Valve or transistor amps. The solid state tended to measure better, but many heard valves as sounding better.

walpurgis

29-12-2016, 10:49

James, Sovereign presently has the LDr loaner unit which I built many years ago. I will arrange with James for its return here to New Zealand- to update its boards, then provide it back so each one of you can hear what we are hearing - does that sound like a good idea ?

There are those who will refuse to listen to it. They will not accept that it can be good, as it won't measure in a way that suits their 'technical parameters'!

Clive

29-12-2016, 10:55

I concur with the posts that say TVCs / AVCs sound clearer / better than pots and sw atts. This fidelity is nothing like the tailoring of sound which SE amps can bring in that the TVC / AVC sound is generally very pure and unadulterated.

Light Dependant Resistor

29-12-2016, 10:57

There are those who will refuse to listen to it. They will not accept that it can be good, as it won't measure in a way that suits their 'technical parameters'!
Yes there will always be a minority like this, but WHY their technical parameters = prejudices, cause this- you have to wonder ? A cloth might help - where it is placed might have to be discussed.:)

walpurgis

29-12-2016, 11:02

Oh. And by the way Chris. If there is a 'loaner' LDR to be available. I'd like to try it!

Light Dependant Resistor

29-12-2016, 11:07

Hi Geoff
It should be back in the UK early February, so you are first on the list.
I have asked James to be its guardian with loans out of 2 weeks duration
then back to James. Thanks

Cheers / Chris

Light Dependant Resistor

29-12-2016, 11:08

Sorry posted twice.

walpurgis

29-12-2016, 11:13

Hi Geoff
It should be back in the UK early February, so you are first on the list.
I have asked James to be its guardian with loans out of 2 weeks duration
then back to James. Thanks

Cheers / Chris

I'll look forward to that. Thanks.

RothwellAudio

29-12-2016, 11:33

Cryptic ? How can an LDR be anything other than an LDR ?
Perhaps you mean removing the mechanical wiping and grinding of conventional pots,
and ridding circuits of signal side input switching, all good reasons why.

Sorry, I don't understand your post, it makes no sense to me.
Let me clarify what I was trying to say. An "LDR passive" is really just a resistor-based potential divider just like a pot or a stepped attenuator. If the other pre-amps being compared by Sovereign were active pre-amps there would be such a lot of circuit differences between them and the "LDR passive" that the specific type of volume control would be swamped by all the other differences. Simply being passive rather than active would be the biggest difference between the LDR passive and the rest of the group.

My views on light dependent resistors as volume controls are that they are just resistors with resistance that depends on the amount of light shining on them, just like the name suggests. However, they're not particularly good resistors compared to what else is available, and controlling them with light makes it difficult to maintain good left/right channel matching. So what's the advantage? Well, it is claimed than the absence of a mechanical contact point is an advantage, but all switches rely on such contacts, as do all audio connectors, so I'm not convinced by that argument. To me it is just a very complicated way to form a potential divider with two resistors. I would prefer to use two good quality resistors and a switch.

Arkless Electronics

29-12-2016, 14:46

Sorry, I don't understand your post, it makes no sense to me.
Let me clarify what I was trying to say. An "LDR passive" is really just a resistor-based potential divider just like a pot or a stepped attenuator. If the other pre-amps being compared by Sovereign were active pre-amps there would be such a lot of circuit differences between them and the "LDR passive" that the specific type of volume control would be swamped by all the other differences. Simply being passive rather than active would be the biggest difference between the LDR passive and the rest of the group.

My views on light dependent resistors as volume controls are that they are just resistors with resistance that depends on the amount of light shining on them, just like the name suggests. However, they're not particularly good resistors compared to what else is available, and controlling them with light makes it difficult to maintain good left/right channel matching. So what's the advantage? Well, it is claimed than the absence of a mechanical contact point is an advantage, but all switches rely on such contacts, as do all audio connectors, so I'm not convinced by that argument. To me it is just a very complicated way to form a potential divider with two resistors. I would prefer to use two good quality resistors and a switch.

Once again I fully agree. LDR's form spectacularly bad resistors with easily measurable and non linear distortion. Even the old carbon resistors from a 1970's TV are wonderful in comparison to a LDR!

Sovereign

29-12-2016, 15:01

:doh::scratch::scratch:

RothwellAudio

29-12-2016, 15:09

:doh::scratch::scratch:

I'm not sure if that means you're baffled or annoyed or something else. Care to clarify?
BTW, what were the pre-amps you compared when you chose the LDR?

Sovereign

29-12-2016, 15:54

I'm not sure if that means you're baffled or annoyed or something else. Care to clarify?
BTW, what were the pre-amps you compared when you chose the LDR?

It
Doesn't mean much mate, I was just imagining my Hifi sounding like a 197"'s tv. I know that wasn't implied, but I found it quite funny.
I compared the LDR with a Croft Epoch, Expo, Naim and DIY class A Pre amp.

RothwellAudio

29-12-2016, 16:28

Perhaps I should mention that I'm actually a big fan of passive pre-amps. Some people say they lack dynamics but I have never found that to be true.
Anyway, it's interesting that you chose a passive pre-amp in preference to four other pre-amps, all of which were active. I probably would have done the same.

Sovereign

29-12-2016, 17:42

Quite a few years ago I let go of an Expo II/IX, back then it was by far the best pre amp I had heard. Maybe I look back fondly with rose tinted glasses but I would love to hear that combination again in the system I have now.

British high fidelity

29-12-2016, 18:30

Hehe i love this forum, i suppose we should add it to the list of great british debates

Rolls or Bentley
Rich tea or Digestives
Cola cubes or pinapple chunks
Roast lamb or Beef

Everyone has there own tastes and wont be swayed, thats whats great and frustrating about this hobby,

And the end of the day ya likes what ya likes

😉

Sent from my LG-H961N using Tapatalk

pgarrish

30-12-2016, 11:16

I'd be interested in trying the LDR when it makes its rounds. I run either a rotel rc850 or a DACT diy passive so it'll be an interesting comparison.

George47

31-12-2016, 14:20

I have been playing with a few passive preamps recently and getting interesting results. I really like the Khozmo passive preamps. They are very well put together and use high quality resistors. If you are feeling flush then they make an up-market version, the Hattor. It comes in a really natty box, has very high quality resistors, remote control, balanced input/outputs and is remote controlled. It sound is among the best I have ever heard. It has the dynamics and bass that some passives seem to lessen.

I have tried a lot pf TVCs and their quality seemed variable depending on what I used them with. The music First copper did not work so well with the Audio Research Ref 110 so I bought an ARC Ref 3. The Townshend Allegri did not work ideally with a balanced only input Class D but was a real stunner with a Naim. The Townshend was not as good as the Hattor with the Nord Class D.

Never tried LDRs. Do they need to be re-calibrated every so often as the resistance changes with age, for the same amount of light? Could that impact the balance at low volumes??

Light Dependant Resistor

31-12-2016, 15:05

Never tried LDRs. Do they need to be re-calibrated every so often as the resistance changes with age, for the same amount of light? Could that impact the balance at low volumes??

No if designed properly.

There is misconception I think again here with comment like, "the same amount of light" with the construction of LDR's

The type used to act as sensors for street lamps and ovens and many other purposes, are open face types, are NOT the type used for audio purpose circuits.

An image of each clarifies, they are entirely different devices.

First the open faced type, one would be very silly using these in audio circuits, as they are typically used as a fairly primitive switch.

When the dedicated audio purpose encapsulated type is available
with well published resistance ON and Resistance OFF figures. The NSL32SR3 being one of the best available
capable of varying resistance from 60 ohms to well over 20 mega ohms, IMO

Cheers / Chris
.