Pass' data shows that even if you match two LDRs perfectly e.g. at 1k then they can be so nonlinear as to not match at 200 ohms or ~10k anymore.
From the limited data available this doesn't seem to be excessive, but could still be audible with passive attenuators.
That's why I asked Ryelands about resistances of each LDR at his min/max settings.
However, the OPs device has a calibration mechanism that should fix that.
Yes, the Tortuga attenuator deals with the matching issue by calibrating each LDR at each of the 70 attenuation steps, logging the results into an EEPROM memory chip, and then reading back that stored DAC command value (a voltage) to achieve the needed resistance for whatever attenuation step the user selects. If the LDRs performance curve drifts over time, repeating the calibration corrects for this.
I've not followed this thread for some time now and having caught up I offer this synopsis of what I've read here from the outset.
1) LDRs do indeed have higher distortion than resistors or pots. The manufactures actually document this. I believe that info was shown at some point in this thread. I don't think anyone is seriously claiming otherwise.
2) Experts therefore have concluded that on the basis of this, plus perhaps some other aspects of LDRs such as their inherent nonlinearity, that LDRs MUST BE, in fact ARE, inferior to resistors and pots for attenuation.
3) #1 & #2 notwithstanding, the perceived results from 100's if not 1000's of users who've actually listened to music through LDR attenuators in comparison to their conventional preamps with pots and stepped attenuators, are almost universally in agreement that the music sounds better coming through LDRs. It's not unreasonable to infer from this that the relatively higher distortion and nonlinearities etc. simply aren't sufficient to have a materially adverse effect on the quality of the audio as perceived by listeners and that perhaps the unique conductive material in LDRs through which the audio signal passes may in fact have everything to do with why they sound better.
4) Because of #2, experts are of the view that #3 is either factually incorrect or that users only think LDRs sound better or are perceiving distortion as something pleasant or may possibly be delusional and that commercial purveyors of LDR attenuators are at best sharing in this delusion or are otherwise knowingly selling snake oil to the great unwashed.
5) Experts do not need to listen to music through LDRs to be certain of their conclusions and therefore aren't interested in doing so.
I readily admit that I've absolutely no idea how to resolve this conundrum. I do, however, own a pair of ears and know how to use them. I like what I hear. So do most who've also listened. That's all I've got. Namaste.
6) Users of LDR's have no interest in exploring the possibility that there is a measurable and audible effect going on that is a difference engendering their preference.
Reverb boxes are not snake oil, (that's an exaggeration to make a point). I have friends that ALWAYS prefer listening with a little added reverb.
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Really? I think the contributions on this thread make it clear that a substantial number of those who have listened have reached the opposite conclusion.
Of course, since virtually none of these experiences are in the context of a controlled test where the LDR vs pot was the only changed parameter (vs different input/input impedances or surrounding circuitry like buffers) it' hard to draw much of a conclusion from any of them.
Peace to you my friend.
I've read this over several times and I'm not sure I understand it. Are you suggesting that some users have a preferred type of sound (a listening bias if you will) that LDRs happen to match and thus LDRs are perceived as sounding better when objectively they don't ?
That statement has no meaning there is no objectively something has to sound better. There is a group of folks that like flea power SET amps and ultra efficient horn speakers, good for them far be it for me to judge their opinions one way or another.
What's the matter with LDR's are an effects box that some folks like, if that was the case? Why is this scenario so threatening?
MY guess is that because people switching from stepped attenuator dont find the LDR coloured one bit and find them in the contrary often even more transparent then their technically better stepped attenuator.
It seems a bit inflammatory to call ldr attenuator effect boxes.
They either sound different than a conventional line stage or they don't. If they do, they're distorting the signal. It's an effect. If you like that, fine, it's your system and you're the only one it needs to please.
Each time I visit this thread I'm struck by the harsh combative tone of many of the comments. As though it's not enough to simply politely and clearly state a view or site a fact but it has to be jammed in there and twisted off or stomped on because somebody is wrong dammit so wrong and you are right so right. Outa here.
"Don't like" I guess you are not even listening. I asked "entertain the possibility" that the distortion etc. was an audible effect. I guess that's too much.
It either sounds the same as a conventional line stage or it doesn't. If it doesn't, it is audibly distorting the signal and that's an effects box. You may or may not prefer that to a conventional line stage which does not audibly distort the signal.
Do you honestly think my comments are combative or they simply beg a little examination of your claims?
Scott, I think that this post (from another thread in this forum may give you some data to chew on:
http://www.diyaudio.com/forums/anal...ource-selection-controller-2.html#post4460058
Note that the model numbers of the LDR units are shown in the figure that is attached to that post.
On the other hand, I have seen some measurements that show that at modest voltage levels the level of distortion in the LDR does become something much more than negligible. For instance, the plot below of a Vactrol (the exact model is not divulged) is an example of this:
Photo source: https://en.wikipedia.org/wiki/Resistive_opto-isolator
Frankly, it's my opinion that even if an LDR volume control had 0.1% distortion (or even more) most people would not notice or care.
.
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so all conventional line stage sounds the same?
''conventional line stage''. what is that? TVC? Buffers with pot? Stepped attenuator? Tube pre amp?
Because I have seen many comparison between ''conventional line stage'' and they dont seem to all sound the same.
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You didn't answer my question and someone else has also asked the same question. You brought it up. You should be able to back it up and provide an answer. Instead, you sort of evaded things with your answer.
Also, as to "effects box" comments.....
You have a stated preference for tubes, designing with them, etc. You are an expert on effects boxes. I guess the ones you like are okay and the ones you don't like are damnable.
Scott, this is what I was referring to. It is the first time the "effects box" damnation has entered this thread.
I don't think this is good for the discussion as it is very inflammatory.
SY also believe that his computer soundcard DAC is as good as it gets and that any DAC that function and measure properly, and theres many dac that indeed do measure extremely well, will all sound close to identical in a blind test. IIRC, when questioned about why he thought that and if he had tried many other dac in his system to come to such conclusion, he said that he didnt have to try other dac, that the measurements was enough.
LOL
I have read enough people commenting on how transparent they are that to call them effect box seems exaggerated.
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Hi, I'm the OP of this thread and started it all by writing my listening impressions of my LDR unit in comparison with my stepped attenuator.
The term "effects box" is generally used in context to dismiss and damn a piece of audio gear that the writer finds deficient. I don't think that has any place in this thread.