Are LDR pres the ultimate passive?

[Wakefield Turntables]

Are you suggesting I've got flaws?

You've probably got several in your abode! Sorry.... I'll get my coat...

[Bonky]

I notice that Angle Audio here in the UK do a LDR preamp. I can get onto their website (http://www.angleaudio.co.uk/index.asp), but no more details seem to be forthcoming. (Mind you our BT landline and BB is hopeless at the moment).

Does anyone know more? Review/Comparison?

Bouncy.

[Marco]

Science... so much of it is based on the status quo and community views; many "radical" theories initially rejected because of opinion and ego, human herd mentality, not because of "science", but then the evidence comes along... new evidence, previously unmeasurable evidence... the loonies vindicated.

Ha- how true is that, especially the bit in bold!

The point you're making, Neil, is largely why my signature, below in blue text, exists: if you have what you consider good reason, always challenge 'currently accepted wisdom'/the status quo, and the contextual validity of 'scientific proof', as it's the only way new things are learned!

Marco.

[Light Dependant Resistor]

Hi
It is interesting we seem to accept loudspeaker distortion in its many forms as though
it cannot be improved upon, even though it is there. Marco's earlier
comments have had me thinking about how we perceive and accept
various aspects of audio. Clicks and imperfections on a LP might be another.

But Marco's comments went further, outside of the square so to speak - very interesting.

An article here http://www.enjoythemusic.com/magazine/bas/0708/
has the writer fed up as he says.

"I am fed up with individuals who claim they can hear the difference between a power amplifier with 0.05 and 0.01 percent distortion while ignoring distortion that is 10 to 100 times greater in the loudspeakers. For the most part, I believe these people are not saying anything about the quality of the equipment, but rather are simply giving their opinions about what kinds of distortion they like"

Cheers / Chris

[lurcher]

Hi
It is interesting we seem to accept loudspeaker distortion in its many forms as though
it cannot be improved upon, even though it is there. Marco's earlier
comments have had me thinking about how we perceive and accept
various aspects of audio. Clicks and imperfections on a LP might be another.

But Marco's comments went further, outside of the square so to speak - very interesting.

An article here http://www.enjoythemusic.com/magazine/bas/0708/
has the writer fed up as he says.

"I am fed up with individuals who claim they can hear the difference between a power amplifier with 0.05 and 0.01 percent distortion while ignoring distortion that is 10 to 100 times greater in the loudspeakers. For the most part, I believe these people are not saying anything about the quality of the equipment, but rather are simply giving their opinions about what kinds of distortion they like"

Cheers / Chris

Yet, still the claimed advantage of a LDR is the removal of the unmeasurable small distortion caused by switch contacts. Which is it to be? Is distortion important or not?

[Light Dependant Resistor]

Yet, still the claimed advantage of a LDR is the removal of the unmeasurable small distortion caused by switch contacts. Which is it to be? Is distortion important or not?

Of course distortion - namely lowering it, is very important, no argument there.

Looking at a switched attenuator,would you term it as a pure resistance, your answer has to be
NO as each contact the wiper and contact engages is a different form of metal, and is held
in place by a set pressure by the mechanical design. It is inviting errors mixing
different metals with arguably little pressure one surface to the next. Partially having
a RCA ( also a primitive form of switch ) in to a socket can create many frequency
spectrum noises if not contacting fully. But taking this further just how much pressure
is enough ? So one piece of metal sliding on another is not good, Relays being
at the top of the ladder but are very rare due to complications with requiring so many contacts
and coils . .

Likewise neither is a LDR a pure resistor, rather it is a very special case of device. Those who
claim its opto isolating properties related to L pads and audio circuits, are wrong,
The form used in audio circuits, does not have relationship to circuits originally used in
telephony in Russia, where the anode and cathode of the device were the output, and the
signal side adjusted gain for a amplifier,thereby opto isolating the output. The
signal side of an LDR is as simple a pathway from source to load as you can get.
There is no isolation or opto coupling on the signal side. Rather the mechanism
by which attenuation is altered from low to high is indeed opto isolated.

LDR's exhibit a marvellous silencing attribute, that enables the source component and amplifier
to be what appears to me as - as one.

It as though every connection from the source to the load has been welded, and as though there is far
more transferred in terms of signal.akin to a perfect transmission line.

I have personal experience of this every day, *I can and I do trial other attenuators
but they are poor, to very poor in comparison.

Cheers / Chris

[Reffc]

Is not the over-riding argument for the designer one of acceptable limits and good practice? If there are several ways to make a preamp circuit, and one method results in say 2% distortion and the other, 0.02%, and that circuit is not a great deal more costly to build, then that is an obvious area where one would assume good practice and what can be practicably achieved ought to be achieved. Where differences between amps might be 0.01% and for arguments sake 0.005%, but there is additional cost/complexity to delivering that, then I question very much whether it's good practice at all, given the additional resources for practically no audible gain.

Where loudspeakers are concerned, they are an area where a majority of distortion is not only audible but an order of magnitude greater than that of most amps, so every effort ought to be made to reduce that distortion. A really good loudspeaker (and here, I mean really good) might exhibit between 1 and 2%. The limiting commercial factor is often that what could be better isn't made better as the cost benefit from profitability POV is what drives the result, not necessarily good practice.

This adds another dimension to audio kit and that is at what market price point is it being aimed? This has a huge bearing on performance where some bits of kit are concerned and very very little for others. For speakers, the cost of delivering class leading performance once you reach a certain price point is the care taken in design and specification. No use in using a drive unit capable of 1% at full output (remarkably few are capable of that, but examples include the Scanspeak Revelator and Illuminator midwoofers), IF the crossover design or cabinet are compromised.

Context I think is the key here. For systems with an analogue front end into a valve phonostage, into a preamp, power amp and then speakers, then the sum of the parts matters quite a lot, probably more so than for many digital sources, so keeping the sum of the parts to within tight (ie low distortion) tolerances matters, therefore keeping distortion as low as possible at every step matters more for high fidelity playback. Often pin-pointing what is the major source of the distortions is difficult, so we try and ensure that where possible, things like amps are designed with minimum distortion. Punters will chose things like cartridges on "how they sound" which is one way of saying "the preferred euphonic distortion". Same with perhaps valve rolling where different constructions give rise to differing distortion characteristics.

As mentioned, those claiming to hear minutia details in amps yet listening on so-so loudspeaker systems are possibly not hearing the real differences in the amps at all. Just saying.

[lurcher]

Of course distortion - namely lowering it, is very important, no argument there.

Looking at a switched attenuator,would you term it as a pure resistance, your answer has to be
NO as each contact the wiper and contact engages is a different form of metal, and is held
in place by a set pressure by the mechanical design. It is inviting errors mixing
different metals with arguably little pressure one surface to the next. Partially having
a RCA ( also a primitive form of switch ) in to a socket can create many frequency
spectrum noises if not contacting fully. But taking this further just how much pressure
is enough ? So one piece of metal sliding on another is not good, Relays being
at the top of the ladder but are very rare due to complications with requiring so many contacts
and coils . .

Likewise neither is a LDR a pure resistor, rather it is a very special case of device. Those who
claim its opto isolating properties related to L pads and audio circuits, are wrong,
The form used in audio circuits, does not have relationship to circuits originally used in
telephony in Russia, where the anode and cathode of the device were the output, and the
signal side adjusted gain for a amplifier,thereby opto isolating the output. The
signal side of an LDR is as simple a pathway from source to load as you can get.
There is no isolation or opto coupling on the signal side. Rather the mechanism
by which attenuation is altered from low to high is indeed opto isolated.

LDR's exhibit a marvellous silencing attribute, that enables the source component and amplifier
to be what appears to me as - as one.

It as though every connection from the source to the load has been welded, and as though there is far
more transferred in terms of signal.akin to a perfect transmission line.

I have personal experience of this every day, *I can and I do trial other attenuators
but they are poor, to very poor in comparison.

Cheers / Chris

As I said on the other thread, and will repeat "bullshit".

Yes, I agree, there are non ohmic qualities to a switch contct, but as long as the contacting parts are in close enough contact such that the outer electron shells of one atom can exchange electrons with the other, then thats good enough. I have not seen anything thing from the LDR camp about this contact distortion other than words, show me the measurements. I would suspect that the contact induced distortion would be (with a 1v signal) down beyond -140dB if not further.

This mystic LDR you describe in such glowing terms however is a semiconductor device where the bulk resistance is in part controlled by the action of photons creating free electrons. Its is inherently non linear, and its non linear character can be seen to induce distortion at the -50dB level and above. The use of two of them means that distortion vary in level depending how the two LDR's are set (volumn adjustment), and because of there being two, the distortion tends to be odd order in nature, predominately third harmonic.

"LDR's exhibit a marvellous silencing attribute", I would expect that as the non linear behaviour is such that small signals are attenuated more than large ones, creating an apparent and false sense of increased dynamic range.

[Marco]

...and yet none of that translates into it sounding shit (certainly the one Chis has designed, and which I use), or realistically, distinctively worse than either my modded Goldpoint passive or Croft preamp, both of which sound superb, and sonically, the LDR is up there with them, although of course it has it's own 'flavour', as indeed does everything

I think you also know me well enough, Nick, to know that I'm perfectly capable of recognising a genuinely good sound when I hear it, as we've shared each other's company at a number of fests/bake-offs, over the years, and more often than not agreed with each other on such matters [when something sounds good or it doesn't]

Perhaps what I need to do is bring the LDR in question to the next Owston meet, and submit it for the critical appraisal of others and you there, then report the outcome here? I'm more than up for that

Marco.

[lurcher]

You are more than welcome at Owston as you know, many there have heard LDR's some like them others not. Its not a case of "sounding shit" as I have said before, its a case of a audio trick that you either like or not. I (as I said) have no issue with people using them or not, it worries me not at all, but all was looking for is a bit of consistency not hand waving and contradiction. I guess I am asking too much. I built one for someone about 10 years ago and personally didnt like what I heard, they did, so all good. There was talk about them on Audio Talk a few years ago, and I measured some of the coffee boards and published what I found. Its my choice, but if I made any item of audio (other than a guitar effect box) that measured like that, I would not bother putting it in a case. At the best, they solve no problems that not better solved by a cheap stepped attenuator. At worst they introduce audible odd order distortion and an expanding transfer curve into the signal path.

BTW, The level of distortion will vary a lot with the position of the volume control, it may be that in your system Marco, it ends up in a lower distortion position, or it may be that your hearing is tolerant of the particular effect, I can't say.