All of those things are certainly considerations with a circuit of this sort, and the d.c. offset does change with pot rotation but not by much.
I have used it with 5534 and 072 types of op amps and with low impedance's, in my case a 1k input resistor and a 10k pot no oscillations could be induced, this is of course with a proper layout unity gain compensation and low stray capacitance.
The pot has its ends connected from output to inverting input and one end of it is connected to the wiper so that if the wiper does go open the maximum gain can only be ten, in a audio pre amp you would use a 5k pot but mine is used in a test set up.
If you want to d.c. couple it you would use a d.c. offset servo and this of course is always advisable since the source may have a d.c. offset.
rcw
I have used it with 5534 and 072 types of op amps and with low impedance's, in my case a 1k input resistor and a 10k pot no oscillations could be induced, this is of course with a proper layout unity gain compensation and low stray capacitance.
The pot has its ends connected from output to inverting input and one end of it is connected to the wiper so that if the wiper does go open the maximum gain can only be ten, in a audio pre amp you would use a 5k pot but mine is used in a test set up.
If you want to d.c. couple it you would use a d.c. offset servo and this of course is always advisable since the source may have a d.c. offset.
rcw
No, there hasn't. There have also been no controlled listening tests to demonstrate any superiority or, for that matter, any audible differences between a conventional circuit and the LDR circuits.
As I said, I have offered as much evidence as those who like LDR attenuators. However, a symmetric non-linear resistor (e.g. LDR) will generate odd-order distortion if there is no DC bias, and if the non-linearity is smooth then the distortion will be dominated by third-order for most reasonable signal levels. The only part of that sentence which is a "guess" is the word 'symmetric'; as this is the best case you would be wise not to argue with it, because an asymmetric non-linear resistor would almost certainly generate more distortion. The remainder is just standard knowledge.Ryelands said:
The two groups are both humans listening to audio systems. It is unlikely that 60 years is enough time to radically change the performance of the human auditory system. If some people preferred distortion then, it is likely that some people prefer distortion now. What do we find today? Some people prefer circuit topologies which produce non-negligible amounts of low-order distortion.
As I was not writing a scientific paper I did not consider it essential to provide full referencing for all my statements. Can you give the exact source for every opinion you hold?
I have no idea what you mean by this.
I too deprecate arguing from authority. Far too often on here we get the opposite: arguing from ignorance. However, someone with a recognised qualification in a particular subject ought to know more about aspects of that subject than someone with no such qualification, especially if the latter has already demonstrated their confusion. In that sense the authority is not "spurious". Of course, there are EEs who have forgotten what they learnt and some EEs who perhaps misunderstood what they were taught, and even a few who were taught wrongly.
Arguing from truth is the best option, but even that doesn't work with some people if they lack even basic knowledge. Whether people like it or not, electronic engineering is based on facts. Ignorance of them or denial of them does not render them false.
Maybe - but, as your point is that they offer no evidence, it doesn't do much for your case. You supported Ian Miller's snide claim that those who liked LDR-type volume controls were, for all practical purposes, George's groupies by adding that they have a fondness for a little distortion when listening to recorded music and were in any case predisposed to dislike electrical engineers. My point is that your argument not only doesn't hold water but betrays an ignorance of the ABC of psychology every bit as profound as the ignorance of electronics you claim to detect in "audiophiles".
(Just for the record, my guess is that Miller's engineering qualification is not in electronics and that he is, as far as audio goes, a hobbyist, same as the rest of us. Nothing wrong with that of course.)
Dear, oh dear. Where to start? You haven't even demonstrated that they are listening to comparable systems or sources. Perhaps you think that doesn't matter but, as Moir's claim - or, to be accurate, what you think was Moir's claim - relied by definition on the performance of tube amplifiers and (at a guess) the best LPs of fifty-odd years ago, you're making the mother of an assumption. Not only is your recollection of his work hazy but you haven't a clue what amplifiers or sources are preferred by current owners of LDR devices. I suspect, for example, that those (such as me) who use good-quality transistor amplifiers would not have fallen into his "distortionophile" group.
This really is very basic psychology ("standard knowledge" even) that, in your words, "you would be wise not to argue with". Though I fear you will.
Of course not - no one is suggesting it has at the physiological level. But if you think there are no socially, culturally and historically-determined parameters in perception (not just audition), you really do have a lot to learn. For a simple but pertinent example, a glance at the literature shows that some musically knowledgeable folk in the era of the 78rpm disc argued that audio reproduction was so life-like that it couldn't, behind the proverbial curtain, be distinguished from a live performer. Today, seriously to advance such a notion would be to invite ridicule. Perceptions - but, emphatically, not the physiology of audition - do change.
Your argument is logically flawed - Group A is contained in Group C and Group B is contained in Group C therefore Group A is identical to Group B. Er, no, it's not. Also, you segued from what you correctly called "an intelligent guess" to regarding an alleged preference for distortion as received fact. To be fair, you seem at least to have dropped your silly point about LDR users being inherently antipathetic to engineers.
Of course not but I'd expect to be challenged if I made offensive remarks in a technical forum while relying on sources I hadn't bothered to check. Different thing altogether. Miller asked for citations and you supported him with a couple of snidies of your own and then banged on spuriously about "peer review". Goose, ganders and all that.
Quite. My training was as an experimental psychologist. I readily admitted to not properly understanding your point about distortion in resistors; I respectfully suggest that you, in turn, drop the cod psychology.
Incidentally, SY notes that "There have also been no controlled listening tests to demonstrate any superiority or, for that matter, any audible differences between a conventional circuit and the LDR circuits".
That's true but SY might care to look at what John Curl writes about "controlled tests" - he's one of the few electrical engineers I've read in many a year who seems to grasp the issues with "controlled tests". Most engineers, however superb they are in their field, have little or no understanding of what it takes properly to "control" a test. Simply shouting "controlled test" or, worse, "double-blind" is not enough.
You said that "Cyril Bateman was, I believe, employed by one of the capacitor manufacturers". Well, I suppose that's true but it would have been more helpful to recognise that he was also, as a few seconds on Google would have shown, one of those much-respected engineering professionals you claim to respect, not least because it was you who accused me and others of being antipathetic to expertise.
I wasn't aware that I was doing any psychology, cod or otherwise.Ryelands said:
As well as not referencing original sources in a web forum discussion, I also do not Google all the opinions I offer or statements I make. Neither, I suspect, do you. I am still somewhat baffled by your stance on this: I was merely trying to point out that Bateman is a serious engineer not some random audiophile with a 'bright idea'. It seems that when you don't disagree with what I say you seem to disagree with the way I say it. This makes discussion difficult.Ryelands said:
On the contrary, this is precisely the point. There is now a social and cultural expectation in audio that certain things are good and certain other things are bad, in some cases despite careful engineering indicating the opposite and in some cases perhaps because careful engineering indicates the opposite. Perhaps as a psychologist rather than engineer you are not always in a position to judge when this occurs (i.e. preference being opposed to engineering).Ryelands said:
I think Stuart is well aware of what JC thinks of controlled tests.Ryelands said:
If by "grasp the issues," you mean, "is completely in denial or ignorant about human sensory perception and testing," then yes. No-one (least of all me) argues that engineers should be setting up sensory tests without assistance from specialists in that field- this is how I learned. But that's a complete red herring.
He he, these arguments just float around once in a while. One thing that bothers me is that when most people use a different design and hear a difference, regardless whether it's an improvement or not, we tend to attribute it to the change itself and ignore the fact that circuits act as a whole. So if you hear an improvement, and measure an improvement, then it most likely in an improvement. If we hear an improvement but do not measure and improvement, it's necessary to measure the total system rather than just a device. Sometimes nonlinearity or asymmetric in one location compensates for the characteristics in another location. Speaker drivers are most likely to have asymmetric BL curves for example...
If degradation is heard and the measurements of a device show improvement, does this mean we have junk elsewhere in the system? Or have we not measure the right characteristics?
If degradation is heard and the measurements of a device show improvement, does this mean we have junk elsewhere in the system? Or have we not measure the right characteristics?
Finally finished my new LM4780 amp and PSU and fitted my LightSpeed Attenuator in it. Haven't had much time to listen to it, but it sounds pretty sweet, probably better than my old chip amp I made.
http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-219.html#post3119597
http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-219.html#post3119597
DF96,
As seems to often be the case, the question is probably, "How MUCH distortion?".
I gather that you meant that a curve in the resistor's V-I (voltage-vs-current) plot would cause the distortion you mentioned. Please correct me if that assumption is wrong.
Intuitively, it seems almost certain that it would cause some amount of some kind of distortion, if the V-I characteristic were not linear, around a fixed resistance setpoint. But, to be fair, if the distortion level was, for example, 0.00000000001%, then it would be utterly negligible.
Without first determining at least the order of magnitude's neighborhood, it almost seems wrong to even mention it in the presence of non-EEs. <grin>
Anyway, I don't know either. But I also wasn't aware that a CdS (Cadmium Sulfide) cell's V-I characteristic is non-linear, when the illumination is not varying.
Remember that we CAN'T consider the LED-LDR or R-vs-lux curves:
After the volume knob has been set for a fixed attenuation level, the LED's I-vs-V and the LDR's R-vs-I and the CdS's R-vs-lux response curves are totally out of the equation.
At that point, it's just a CdS cell with a fixed resistance setpoint, with non-varying illumination.
Are you saying that the CdS cell's V-I plot is curved, when the illumination is NOT varying? (Sorry, I guess I could look it up, myself...) Interesting.
Edit: See Figure 4 I on page 198 or so of
downloads.hindawi.com/journals/apec/1981/372454.pdf
Cheers,
Tom
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Here's a diyaudio post/thread where they say the NSL-32SR2 can do -130 dB distortion:
http://www.diyaudio.com/forums/equi...signs-new-super-oscillator-4.html#post2679483
It looks like it will do down to a hair over 0.003%, if the signal level is at -15 dBu.
http://www.diyaudio.com/forums/equi...signs-new-super-oscillator-4.html#post2679483
It looks like it will do down to a hair over 0.003%, if the signal level is at -15 dBu.
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How does -130dB for distortion from post37 come from the data shown in post35?
http://www.diyaudio.com/forums/equi...designs-new-super-oscillator.html#post2678868
http://www.diyaudio.com/forums/equi...designs-new-super-oscillator.html#post2678868
Figures I have seen for LDR attenuators are in the region of 0.01-0.1% distortion for signals around 1V. Small, but not necessarily entirely negligible. Perhaps many orders of magnitude larger than the distortion of a normal pot? Why should we drop something with almost immeasurably small distortion for something with much more distortion?
Google 'LDR attenuator distortion'. I understand some optoisolator manufacturers publish their distortion curves?
Google 'LDR attenuator distortion'. I understand some optoisolator manufacturers publish their distortion curves?
It always amazes me when people get all concerned about hundredths of a percent distortion in electronics, when speakers have 1,000 times more distortion (or more). There was a time when .1% was considered distortionless. Then is became .05%, then .001%. I won't even bother to comment on single ended tube equipment.
The distortion plot was at the link I gave for the "Jim Williams..." thread. It shows about 0.003% as a minimum, for a -20 dBu signal level (I think it was).
Anyway, the reason that someone would "drop something with almost immeasurably small distortion for something with much more distortion" is because the distortion doesn't generate sufficient weighting in their optimization metric to prevent them from doing that. i.e. They want to.
If I recall correctly, one of George's concerns was mechanical contacts, and some of the sound-quality-threatening effects associated with them. And to be fair I can easily imagine an old dirty pot causing a lot of distortion, and worse.
But my main concern was that you might have been confusing the non-linearities associated with changing the resistance setpoint with a non-linear V-I characteristic after the setpoint was established, when none of the LDR-response non-linearities are still present.
I haven't seen any data that suggests that the V-I characteristic of a CdS photocell is non-linear, once it is at a particular resistance value.
It might be non-linear, and probably is, slightly, based on the distortion plot I saw. But I haven't found any good data on the non-linearity itself. And the one plot I found shows NO non-linearity.
Of course, everything is probably non-linear at some point, to some degree. Plain resistors are non-linear due to heating effects interacting with their temperature coefficient when the current level changes with an AC signal. That effect is said to actually be significant-enough for audio that some designers use over-sized resistors where it might matter. The same type of effect has been noted with in-line fuses for speakers.
But George is probably right that the distortion level is so low that it's not significant.
Cheers,
Tom
This is the first article I found, I'm sure there are many others.
In this article near the bottom of the first page, the author talks about the diode effect (non-linear effect) between dissimilar contacts in plugs and sockets, which have a far better contact pressure and area than the very lightweight tiny contact area of an audio volume pot (potentiometer).
Passive Intermodulation, PIM Basics :: Radio-Electronics.Com
Cheers George
Very interesting! Almost all gold plated connectors have 90% of nickel. The this is also true with vast gold plated PCBs that use the so called "chemical gold".
If 0.04% can be ignored, why is that the much much smaller distortion from a pot is best avoided?georgehifi said:
No, I am not confusing setting nonlinearity with signal nonlinearity. CdS photocells are a little non-linear, that is why they generate distortion. Not much, but a heck of a lot more than a pot.gootee said:
That is talking about the well-known 'rusty bolt effect'. Applies to dirty or loose contacts passing appreciable signal current levels in lowish impedance circuits, but even then the IM is usually quite small. Irrelevant to audio pots, unless very dirty and feeding a low impedance. Classic FUD technique: find an article which says something different and hope people won't spot the difference.georgehifi said: