I have no motivation to implement your circuit in any particular project
Hi Ian, If you have no motivation to try it, then you won't hear it for yourself.
My own preamp has a conventional capacitor-coupled volume pot
It's a pity then that your source or preceding stage has dc offset and is in need for capacitor coupling, then you will never hear what dc coupling can do for the sound instead of listening to music through capacitors.
It's know fact that two dissimilar metals with light contact points that pots have so as not to wear out the track (wiper "metal" to resistive track "carbon or conductive plastic") with very light pressure can act like a diode, this is why all pots from different manufacturers sound different even though they maybe the same value.
Cheers George
Hi Ian, If you have no motivation to try it, then you won't hear it for yourself.
My own preamp has a conventional capacitor-coupled volume pot
It's a pity then that your source or preceding stage has dc offset and is in need for capacitor coupling, then you will never hear what dc coupling can do for the sound instead of listening to music through capacitors.
It's know fact that two dissimilar metals with light contact points that pots have so as not to wear out the track (wiper "metal" to resistive track "carbon or conductive plastic") with very light pressure can act like a diode, this is why all pots from different manufacturers sound different even though they maybe the same value.
Cheers George
Thanks George. So is there a single technical paper, thesis or other proper scientific study that you can direct everyone to which might quantify the effect in conventional potentiometers that you claim to have ameliorated with your design? And wouldn't the effect be audible in the source material anyway by virtue of the multitude of conventional pots in the recording chain?
Ian wrote: "I have no motivation to implement your circuit in any particular project (especially since it passes the DC current for the LEDs to ground across the wiper contact of the logarithmic/fragile control pot)..."
It is certainly possible to build an LSA with isolation between the signal ground and the ground of the LED power supply/control pot.
It is certainly possible to build an LSA with isolation between the signal ground and the ground of the LED power supply/control pot.
No Ian there's no paper, on what I call dynamic contact bounce, you just have to figure it out for yourself.
But you will never do this as you "have no motivation to implement my circuit in any particular project" anyway even if you do find out for yourself.
The power supply in my circuit has no reference to signal ground.
Cheers George
But you will never do this as you "have no motivation to implement my circuit in any particular project" anyway even if you do find out for yourself.
The power supply in my circuit has no reference to signal ground.
Cheers George
Attachments
It's amazing that there are still people who think that the pot and LEDs are somehow in the audio signal circuit. The fact that the pot and LEDS etc are totally electrically isolated from the signals is the main point of the circuit! No moving parts, no contacts, no ground connections or any connections at all that touch the signal path; just pure resistances controlled by beams of light.
Thank you for that admission George.
I have expressed no concern about your ground isolation as your circuit diagrams and photos of the product's exterior are clear enough on that front. I have merely expressed a concern about the passage of DC across your control pot contacts en route to any ground. Perhaps at least one of your followers might benefit from reading that again. I have used Vactec devices in power limiting circuits and have no trouble understanding the Lightspeed circuit which is somewhat simpler.
George, are you an engineer or a scientist? I ask because your expression "on what I call dynamic contact bounce" suggests an authoritative scholarly stance on a technical phenomenon, but it seems to have undergone a recent and convenient name-change (to something searchable on Google and which you clearly did not coin yourself), so I am left wondering whether you have a degree at all, or are you perhaps making things up as you go?
So without so much as a Wikipedia reference, perhaps instead you could personally demonstrate or quantify what you claim to be the problem of the conventional prior art, rather than expecting people to accept it at face value.
I'm a degree qualified engineer with a few tools at hand today. With a true RMS DMM set to measure diodes, an 1N4004 on my desk reads 0.585V at one polarity and no reading registers on the other. This is an expected result and confirms that the DMM is working. A 10K pot costing $1.95 at Jaycar with the shaft approximately centred measures from one end terminal to wiper terminal at 0.937V in both directions and this is repeatable. Moreover the diode reads as a diode and the track section reads as a resistor. The pot does not measure as a diode by any stretch of my imagination.
A diode rectified sine wave looks something like contiguous smooth hills with sharp valleys in between. My signal generator produces nice clean sine waves from 7Hz to 112kHz. At the output of my preamp I see identically shaped, nice clean sine waves at frequencies right across this range. I see no rectification of the waves whatsoever. In fact with input inverted and summed with the output and with amplitudes matched, my scope displays a straight line with no deviation.
Turning the volume control slowly or quickly while connected to my scope I have never seen anything from my conventional preamp that might be described as a "dynamic bounce", or other pot-turning artefact. Just nice smooth unrectified sine waves of pot-varied amplitude.
In a previous post you said that pots act like a diode and that this is why "all pots from different manufacturers sound different even though they may be of the same value". I have heard unsubstantiated claims to the same from people in your audiophile society which meets at Epping each month. One swore that he could demonstrate a different "tone" in blind tests. As far as I understand it, a different tone would require a change in frequency response and I therefore dismissed the claim. I think that my simple test of the cheapest pot that I could find in my drawer provides sufficient proof to quash the notion. The $1.95 pot that I used (I believe Alpha brand carbon film) has a nice tight/smooth action and I have no reason to suspect that there might be inadequate spring force in its wiper to maintain clean contact with the tracks. I am therefore at a loss to understand a "dynamic bounce effect" during adjustment. I would not choose the dual gang stereo version however as these do not seem to track well. Regular Alps RK27 track fine and I use these for stereo and only with proper capacitor coupling. I would put it to you and your loyal followers that there is no audible difference between pots of different brand/type, and that capacitor coupling is inaudible when the -3dB point is sufficiently below 20 Hz. I notice in this regard that you have not commented on the very obvious point that I raised previously – namely that there are many conventional pots and capacitor coupled connections in the audio path before the music reaches your hi-fi. You have also not addressed the question about the possible insignificance of a single attenuation stage in front of your power amp. I suspect that you cannot.
It is a very easy thing for audiophiles to make unsubstantiated claims in no-cost forums in order to distinguish their wares to a gullible audience. The proponents of open baffle speakers for example conveniently describe the sound of conventional speaks as "boxy". One proponents of an absurd "3D" DSP speaker I saw recently described conventional speaker sound as "2D" after randomly throwing in the name of a scientist whose theorem I am advised by another scientist does not applied to audio. The list goes on. Is it bluff and fluff and nothing more?
It would be an easy come-back for anyone here to ask "but has he tried it with music?" or some such other audiophile challenge, but I am not interested in that as it stands only to illogical reasoning of money-just-spent placebo and not to engineering reason which can be substantiated by measurements.
I notice several quoted incidences of my expressed lack of motivation to implement the Lightspeed circuit in any project. I see that as mere chest pounding and the position has not changed.
I also have no further motivation to return here as I suspect that 475 pages of discussion about something that might amount to nothing is probably ample, and that those involved might be brainwashed to the point of no return. It seems to me to be nothing but a tragic fascination with beams of light in an unnecessarily complicated alternative that perhaps does not work properly.
I have expressed no concern about your ground isolation as your circuit diagrams and photos of the product's exterior are clear enough on that front. I have merely expressed a concern about the passage of DC across your control pot contacts en route to any ground. Perhaps at least one of your followers might benefit from reading that again. I have used Vactec devices in power limiting circuits and have no trouble understanding the Lightspeed circuit which is somewhat simpler.
George, are you an engineer or a scientist? I ask because your expression "on what I call dynamic contact bounce" suggests an authoritative scholarly stance on a technical phenomenon, but it seems to have undergone a recent and convenient name-change (to something searchable on Google and which you clearly did not coin yourself), so I am left wondering whether you have a degree at all, or are you perhaps making things up as you go?
So without so much as a Wikipedia reference, perhaps instead you could personally demonstrate or quantify what you claim to be the problem of the conventional prior art, rather than expecting people to accept it at face value.
I'm a degree qualified engineer with a few tools at hand today. With a true RMS DMM set to measure diodes, an 1N4004 on my desk reads 0.585V at one polarity and no reading registers on the other. This is an expected result and confirms that the DMM is working. A 10K pot costing $1.95 at Jaycar with the shaft approximately centred measures from one end terminal to wiper terminal at 0.937V in both directions and this is repeatable. Moreover the diode reads as a diode and the track section reads as a resistor. The pot does not measure as a diode by any stretch of my imagination.
A diode rectified sine wave looks something like contiguous smooth hills with sharp valleys in between. My signal generator produces nice clean sine waves from 7Hz to 112kHz. At the output of my preamp I see identically shaped, nice clean sine waves at frequencies right across this range. I see no rectification of the waves whatsoever. In fact with input inverted and summed with the output and with amplitudes matched, my scope displays a straight line with no deviation.
Turning the volume control slowly or quickly while connected to my scope I have never seen anything from my conventional preamp that might be described as a "dynamic bounce", or other pot-turning artefact. Just nice smooth unrectified sine waves of pot-varied amplitude.
In a previous post you said that pots act like a diode and that this is why "all pots from different manufacturers sound different even though they may be of the same value". I have heard unsubstantiated claims to the same from people in your audiophile society which meets at Epping each month. One swore that he could demonstrate a different "tone" in blind tests. As far as I understand it, a different tone would require a change in frequency response and I therefore dismissed the claim. I think that my simple test of the cheapest pot that I could find in my drawer provides sufficient proof to quash the notion. The $1.95 pot that I used (I believe Alpha brand carbon film) has a nice tight/smooth action and I have no reason to suspect that there might be inadequate spring force in its wiper to maintain clean contact with the tracks. I am therefore at a loss to understand a "dynamic bounce effect" during adjustment. I would not choose the dual gang stereo version however as these do not seem to track well. Regular Alps RK27 track fine and I use these for stereo and only with proper capacitor coupling. I would put it to you and your loyal followers that there is no audible difference between pots of different brand/type, and that capacitor coupling is inaudible when the -3dB point is sufficiently below 20 Hz. I notice in this regard that you have not commented on the very obvious point that I raised previously – namely that there are many conventional pots and capacitor coupled connections in the audio path before the music reaches your hi-fi. You have also not addressed the question about the possible insignificance of a single attenuation stage in front of your power amp. I suspect that you cannot.
It is a very easy thing for audiophiles to make unsubstantiated claims in no-cost forums in order to distinguish their wares to a gullible audience. The proponents of open baffle speakers for example conveniently describe the sound of conventional speaks as "boxy". One proponents of an absurd "3D" DSP speaker I saw recently described conventional speaker sound as "2D" after randomly throwing in the name of a scientist whose theorem I am advised by another scientist does not applied to audio. The list goes on. Is it bluff and fluff and nothing more?
It would be an easy come-back for anyone here to ask "but has he tried it with music?" or some such other audiophile challenge, but I am not interested in that as it stands only to illogical reasoning of money-just-spent placebo and not to engineering reason which can be substantiated by measurements.
I notice several quoted incidences of my expressed lack of motivation to implement the Lightspeed circuit in any project. I see that as mere chest pounding and the position has not changed.
I also have no further motivation to return here as I suspect that 475 pages of discussion about something that might amount to nothing is probably ample, and that those involved might be brainwashed to the point of no return. It seems to me to be nothing but a tragic fascination with beams of light in an unnecessarily complicated alternative that perhaps does not work properly.
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"I'm a degree qualified engineer with a few tools at hand today. With a true RMS DMM set to measure diodes, an 1N4004 on my desk reads 0.585V at one polarity and no reading registers on the other. This is an expected result and confirms that the DMM is working. A 10K pot costing $1.95 at Jaycar with the shaft approximately centred measures from one end terminal to wiper terminal at 0.937V in both directions and this is repeatable. Moreover the diode reads as a diode and the track section reads as a resistor. The pot does not measure as a diode by any stretch of my imagination."
As such a smart person surely you listen to DC voltage daily.... ??
And no I am not George. But at least he has SHARED a design with the forum, what have you shared other than opinion?
George has thrown a design out to a group and has been man enough to stand behind it.
As such a smart person surely you listen to DC voltage daily.... ??
And no I am not George. But at least he has SHARED a design with the forum, what have you shared other than opinion?
George has thrown a design out to a group and has been man enough to stand behind it.
From an interview with Hervé Delétraz owner/director of DarTZeel audio, I dare say with more street cred than you, Ian
"Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light, there is no "diode effect," either electrical or chemical (electrovalence differential), to alter the signal. However, until all the patents are in place, I would prefer not to specify the details."
Needless to say this patent was not granted as I made the first Lightspeed Attenuator back in 1975. But it does not stop anyone like Herve from using it, as I did not patent it back then either.
Also Mark Porzilli of Melos fame used it in the mega dollar Melos SHA Gold Reference pre in the 90's, he called it Porzilli Potentiometer, but ldr's were very crude then and they all came back under warrantee, this is maybe what sent Melos broke.
"I also have no further motivation to return here" I am so broken hearted
that you will not even listen to one for yourself.
6moons audio reviews: darTZeel NHB-18NS
darTZeel NHB-18NS preamplifier | Stereophile.com
darTZeel NHB-108 Model One power amplifier | Stereophile.com
Cheers George
"Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light, there is no "diode effect," either electrical or chemical (electrovalence differential), to alter the signal. However, until all the patents are in place, I would prefer not to specify the details."
Needless to say this patent was not granted as I made the first Lightspeed Attenuator back in 1975. But it does not stop anyone like Herve from using it, as I did not patent it back then either.
Also Mark Porzilli of Melos fame used it in the mega dollar Melos SHA Gold Reference pre in the 90's, he called it Porzilli Potentiometer, but ldr's were very crude then and they all came back under warrantee, this is maybe what sent Melos broke.
"I also have no further motivation to return here" I am so broken hearted
that you will not even listen to one for yourself.
6moons audio reviews: darTZeel NHB-18NS
darTZeel NHB-18NS preamplifier | Stereophile.com
darTZeel NHB-108 Model One power amplifier | Stereophile.com
Cheers George
Let us assume a conventional pot has a somewhat diode-like response at the wiper-track interface, as is claimed. How do we deal with that? Simple: follow the pot with a high impedance buffer. The part of a conventional pot which could cause problems is the end connections to the track, because a buffer would not solve that, but that would be the same problem as any resistor so if pots are bad then resistors are bad too. Try building a circuit with no resistors! So normal pots either have no problems, or soluble problems, or problems so bad that no resistors can be used at all.
Now consider LDRs. They are known to be slightly non-linear, so except at -6dB attenuation with identical resistances they will introduce a little low order distortion. Probably mainly second, so fairly harmless. It was established back in the 1950s that some people prefer sound with a little addition of low order distortion - it sounds 'richer'.
I think I know why some people prefer LDR attenuators. It is for the opposite reason from what they think. Others may simply prefer what they regard as an 'anti-establishment' position: if EEs like it then they are against it. Each to their own.
Now consider LDRs. They are known to be slightly non-linear, so except at -6dB attenuation with identical resistances they will introduce a little low order distortion. Probably mainly second, so fairly harmless. It was established back in the 1950s that some people prefer sound with a little addition of low order distortion - it sounds 'richer'.
I think I know why some people prefer LDR attenuators. It is for the opposite reason from what they think. Others may simply prefer what they regard as an 'anti-establishment' position: if EEs like it then they are against it. Each to their own.
Ian, forgetting the hypothesis of contact bounce, do you have any direct experience comparing your 20 yr. old pot to anything? There is a wide audience for stepped attenuators, TVC and AVC volume controls, that extends well beyond this thread. Is the entire market for such things a hoax? I'm a parts supplier to high end audio OEMs. Through a fairly broad survey I've encountered more than a few OEM designers who believe that above a certain level of refinement, most of difference that can be heard between top preamps resides in the volume control.
It's disputable to assert that the properties of the volume control used in playback are undercut by the pot used in recording. For most audiophiles, through many tweaks and upgrades it becomes obvious that the "weakest link" theory doesn't really apply to high-end audio. The recording and playback chain is full of weak links and the gap between recorded and live music is large enough that an improvement in almost any area is perceptible.
It is certainly reasonable--and particularly reasonable to a EE-- to limit experiments to those that he considers reasonable.
It's disputable to assert that the properties of the volume control used in playback are undercut by the pot used in recording. For most audiophiles, through many tweaks and upgrades it becomes obvious that the "weakest link" theory doesn't really apply to high-end audio. The recording and playback chain is full of weak links and the gap between recorded and live music is large enough that an improvement in almost any area is perceptible.
It is certainly reasonable--and particularly reasonable to a EE-- to limit experiments to those that he considers reasonable.
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That's barely even a hypothesis, just a guess for which you produce no evidence. Ian Miller BTW uses that most irritating of ploys, argument from authority [I'm a degree-qualified engineer (in?) and I want to see a paper with a long title because I KNOW you're wrong].
I use an LDR device for volume control because it sounds better than the stepped attenuator I was using previously; the difference is not trivial. I'm sorry if you can't replicate my results but I don't see how entitles you so carelessly to dismiss those who can. I'm not suggesting that the very best conventional devices would not knock spots of my Lightspeed-type device but, on cost grounds, I'll not be finding out any time soon. LDR devices can be had relatively cheap.
Without accepting much of the tosh put about by "audiophiles" and unscrupulous vendors, recall that the history of audio reproduction provides several examples of phenomena initially dismissed by engineers as absurd that later prove to have merit. The best known is perhaps that different capacitors sound different - no doubt you recall the scorn directed by engineers at those who first argued the point. The phenomenon has, of course, since been given a sound empirical basis by makers and designers of capacitors aimed at the audio sector. Thankfully, they eschewed pop psychology and focussed on what they do best.
It is a hypothesis. An educated guess is the source of most hypotheses. I have produced as much evidence as those who claim that LDR attenuators are good.Ryelands said:
He did not. He simply asked for peer-reviewed evidence or reasonable explanation, the normal standard in science and technology. No length of title was specified. If I read him correctly he is saying "I think you are wrong but I am willing to be convinced otherwise so show me the evidence". As is often the case in 'high end' audio all he was offered was a mixture of anecdote and sneering.Ryelands said:
You will accept, I am sure, that this does not refute my hypothesis. It could serve to confirm it. I would expect a small but non-trivial difference, measurable as low levels of low order distortion.Ryelands said:
It might be more accurate to say that the phenomenon has been given a sound scientific basis by makers and designers of capacitors aimed at the precision industrial sector.Ryelands said:
Sorry but it wasn't an "educated guess", it was two instances of run-of-the-mill pop psychology. Firstly, though I'm not exactly sure what you mean by "LDR non-linearity and distortion", to say "probably mainly second, so fairly harmless" is, of course, to guess, not to submit evidence.
Secondly, and more critically, "It was established back in the 1950s that some people prefer sound with a little addition of low order distortion . . ." is misleading unless you can show that the "some" who preferred all those years ago a little distortion with their soup can safely be included in the same group as those who today prefer LDR volume controls. Almost by definition, they can't be.
In passing, I'd add to David Garretson's useful points that those who "claim that LDR attenuators are good" have designed, built and used products, often over a period of years whereas you've made a couple of blanket statements which, on examination, turned out to be pretty much plucked out the air. That doesn't make you wrong - but it doesn't make you very convincing either.
The length of title bit was, as I hoped was obvious, a quip, a light-hearted dig at what I saw (since you force the issue) as Millar's heavy-handed, not to say pompous, prose. If it wasn't obvious, I apologise. That said, he made no reference to peer review, in any case a notoriously poor index of a paper's technical merit.
I don't think you do read him correctly. His question was framed in a manner that borders on solipsism, which was why it irritated me. The first (and, arguably, the only) resort to sneering was his, not mine, in his use of phrases such as "would you care to substantiate the basis of the belief and/or direct your followers . . .". That suggests to me a determination not to be reasonable, not at any price.
Of course it doesn't. But it doesn't support it either, not least because Millar was discussing elderly pots of conventional design.
IIRC, pertinent distortion measurements have been reported on this thread but I could well be wrong and do not plan to look. Whatever, you can expect a host of things and George S a barrow-load of different ones but a good start, if you're serious about the topic, might be to ask for subjective reports of what differences users hear between the two technologies to see if they lend any support to your notion that enthusiasm for LDRs is essentially a re-run of an uncited result from sixty years back.
Note also BTW that Millar is implying that suppliers and users of LDR-based devices have about them something of the cult whereas you are suggesting only that they like a touch of second-order distortion which, you're guessing, is to be found in this application. The arguments are very different, yours having the merit of not being offensively phrased.
And it might not be. We were recently reminded over on John Curl's thread of Cyril Bateman's explicitly audio-related reports on the topic (with a clue in the title of one of them, "Capacitor Sound"). I'm not sure what the "precision industrial sector" is though I take your wider point that other sectors also had an interest in confirming and quantifying what (degree-level) engineers in the audio-sector had prior dismissed out of hand.
I mean LDR voltage non-linearity i.e. an LDR is not a perfect resistor whose value is set by the light intensity. It is good, but less so than a normal resistor. This non-linearity will produce signal distortion, related to signal level. On reflection it will probably be mainly third order, rather than the second order I stated.Ryelands said:
My remark about title length was also a quip, aimed at what I saw as possible anti-intellectualism (very common in audio); I apologise if I have jumped to conclusions. I agree that peer review is a poor guide to merit, but it is better than the absence of peer review.
My mention of a preference by some listeners for some distortion I believe arises from a comment made by James Moir in his 1961 book "High Quality Sound Reproduction", when he was reporting on published research. However, a quick look just now has failed to find the relevant section, so either I have to look harder or I saw it elsewhere. The same phenomenon, if valid, could explain some of the popularity of SE amps.
Cyril Bateman was, I believe, employed by one of the capacitor manufacturers. I note your apparently negative attitude to those who you believe may have degrees.
Has anything been measured?
Has there been anything measured that explains the great sound that results from the lightspeed attenuator?
I am one of the many that have been using the lightspeed for 4+ years. It simply sounds great. If its distortion get me some more of it. It does seem strange that the addition of distortion could produce what is percieved as sonic cues normally associated with reduction in noise.
Is it simply that the resistive element in the LDR is preferable to that used in typical pots and even in the metal film resistors in stepped attenuators? Many people swear by the value of exotic resistors. Some like ecdesigns hand wind double helix wire wound resistors and swears to their superiority in i/v ciricuits.
The part that I do not understand is why I for one also percieve a not so subtle improvement in SQ when an improvement is made to the quality of the power supply to the lightspeed. One would think that with the isolation provided by the LDR that there would be no difference between a half decent linear power supply and a much better implementation with chokes and low noise discrete regulator. Yet to my ears there was a surprising improvement.
Has there been anything measured that explains the great sound that results from the lightspeed attenuator?
I am one of the many that have been using the lightspeed for 4+ years. It simply sounds great. If its distortion get me some more of it. It does seem strange that the addition of distortion could produce what is percieved as sonic cues normally associated with reduction in noise.
Is it simply that the resistive element in the LDR is preferable to that used in typical pots and even in the metal film resistors in stepped attenuators? Many people swear by the value of exotic resistors. Some like ecdesigns hand wind double helix wire wound resistors and swears to their superiority in i/v ciricuits.
The part that I do not understand is why I for one also percieve a not so subtle improvement in SQ when an improvement is made to the quality of the power supply to the lightspeed. One would think that with the isolation provided by the LDR that there would be no difference between a half decent linear power supply and a much better implementation with chokes and low noise discrete regulator. Yet to my ears there was a surprising improvement.
you will never find anything measured that results in good sound, only what results in bad sounds
but the absence of bad sound would ofcorse result in good sound OK - but that's still a guess, not "evidence".
Fine, fine, fine - but what has it to to do with the topic in hand? No-one bar yourself seems interested in peer review in this context.
Even if you find it (good idea to find these things before quoting them, not after), my point about the non-equivalence of the two subject populations has still to be refuted. The listening preferences of an unspecified sample of listeners using (given the date) tube amplifiers nearly sixty years ago and those of a modern population listening to different (and unarguably superior) sources using different technologies really have too little in common to help us here and even less absent detail. In other words, Moir's book has little or nothing to tell us about the Lightspeed today.
It could at that but it's LDRs we're discussing.
Best not to patronise. At the time of writing, he'd spent 30 years designing capacitors. That's almost as long as it took me to get my degree.
You note wrong. Ian Millar boasted that "I'm a degree-qualified engineer" (the hyphen is mine) though he didn't say which engineering discipline he was qualified in. That said, you're right - I believe he has a degree. Should I be doubting it?
My "negative attitude" is, as explained, to those who argue from authority, especially from the spurious authority of having passed an examination in something or other in one's early twenties.
Much against my better judgment I make a contribution to this thread and present this circuit...
This by far a better device than a ldr attenuator.
If made with a double 5534 type op amp you can use a 1k series resistor that has considerably less thermal noise than any ldr, much less distortion and probably less 1/f noise and since the gain is continuously adjustable and always proportional to the signal level it has a virtually constant s/n ratio, it also has a log law volume control with a linear pot that is far closer to an exact log law than any log pot.
rcw
This by far a better device than a ldr attenuator.
If made with a double 5534 type op amp you can use a 1k series resistor that has considerably less thermal noise than any ldr, much less distortion and probably less 1/f noise and since the gain is continuously adjustable and always proportional to the signal level it has a virtually constant s/n ratio, it also has a log law volume control with a linear pot that is far closer to an exact log law than any log pot.
rcw
This was a thought of mine years ago, till one guru said a pot in the feedback loop is asking for trouble on wide bandwith opamps if it's not set and never turned, once on and turned all hell can break loose with dc offsets/occillations at sometimes high gain. taking out speaker/amps in a split second.
Cheers George
Cheers George