No, but that is completely irrelevant. It doesn't matter what the light source is, an LDR is slightly non-linear in signal voltage terms. The best you can hope for is to keep signal levels sufficiently low that the distortion is low, but it will never be as low as an ordinary resistor or even an ordinary pot.stvnharr said:
LDRs are not "defective" but like all components they have limitations. It amuses me that some people fuss about resistor distortion (vanishingly small) or remove capacitors from "the signal path" while others deliberately introduce non-linear items like LDRs. All claim that their chosen fad is somehow better than normal engineering; they are all mistaken.
As I thought, any application of LDR's is irrelevant. Actual learning about a particular application is just so, beneath you.
Your writing also gives the impression that actual listening to music is also somewhat flawed and irrelevant.
I know that your interest is in the engineering and theory, and not much else.
If you carefully read my writing I have not claimed anything.
There is nothing in my posts about "resistor distortion" or "removing capacitors, etc.
I have just written about what I have heard while listening to music.
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That's the easy way out.
Your evaluation here seems purely subjective (which is perfectly fine) but this a DIY audio forum and many of the gents are interested in the technical aspects of projects and how they perform objectively relative to similar gadgets. Your subjective evaluation leaves no basis for any type of discussion. I'm not sure where you expected this thread to go.
As mentioned by some of the fellas, LDR attenuators have their good points and bad points from a technical aspect.....but it doesn't sound like you're interested in any of that. That's cool, but don't get all huffy when members here point out those technical aspects.
Cheers,
Dave.
As I said nothing of the kind, I can only assume that you have trouble reading English.stvnharr said:
I listen with normal engineering, not to normal engineering. Everyone listens with engineering: the choice is between good engineering or poor engineering.
I note your unwillingness to engage with the actual issue.
That's the easy way out.
Your evaluation here seems purely subjective (which is perfectly fine) but this a DIY audio forum and many of the gents are interested in the technical aspects of projects and how they perform objectively relative to similar gadgets. Your subjective evaluation leaves no basis for any type of discussion. I'm not sure where you expected this thread to go.
As mentioned by some of the fellas, LDR attenuators have their good points and bad points from a technical aspect.....but it doesn't sound like you're interested in any of that. That's cool, but don't get all huffy when members here point out those technical aspects.
Cheers,
Dave.
Yes, Dave you are correct on all points.
Mine is a subjective evaluation. I am not an engineer and mine is not a diy designed unit.
I have been highly impressed with the unit I connected up from the Tortuga controller and psu. The criticism's have not been about that, but have been in more general terms. I thought they could have been a bit more focused on my particular implementation, but it was probably kind of stupid of me to think so.
Probably best to let it all rest.
Thanks for you post.
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Dave,
I edited the quoted material out of my post after thinking about it quickly.
As to the "actual issue"............
As noted in the above post, my subjective evaluation is not really a discussible topic. However, I did think my Tortuga build was a bit discussible. But it gained no interest as nobody is familiar with, or interested in, the Tortuga units.
FWIW, Mort at Tortuga says he has engineered the non linearity out of the LDR's. Maybe so, maybe not. My listening impressions.......
So, best to just let it all go.
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FYI, Mort has his own area over on the Audiocircle jerk forum. Anyone interested can certainly ask him technical questions and/or post their comments there.
Tortuga Audio
Cheers,
Dave.
Tortuga Audio
Cheers,
Dave.
I personally like subjective opinions.
Loudspeakers by the nature of there construction exhibit compression distortion as the voice coil moves out of the gap. LDRs can exhibit compression or expansion distortion based on there resistor ratio. I wonder if there is or can be cancellation of distortion between the ldr and the speaker. It may explain why people seem to have such different reactions to it. Just thinking aloud ....
Loudspeakers by the nature of there construction exhibit compression distortion as the voice coil moves out of the gap. LDRs can exhibit compression or expansion distortion based on there resistor ratio. I wonder if there is or can be cancellation of distortion between the ldr and the speaker. It may explain why people seem to have such different reactions to it. Just thinking aloud ....
I just had a quick look at the Tortuga forum, but could not find any claim about LDR nonlinearity being reduced. Could you direct me? In most cases, the drive circuits for an LDR volume control are aimed at getting the right volume change law or maintaining input or output impedance - this has nothing to do with signal linearity.stvnharr said:
That to me reads like a modification.
Read my post again. I did not say the LED/LDR attenuator was no good.
What I did imply is that one should not attribute magical qualities and claim that it is better when the evidence is there to show that there are very small amounts of added distortion, i.e. less accurate.
HI Andrew,
Sorry if I misunderstood some of your comments.
I didn't claim anything, just reported that I heard improved bass response on some discs, extended dynamic range, and tighter musical images.
I didn't hear any tonal changes between series attenuator and Tortuga unit.
Steve
Hi Dave,
Here's the best I can do:
What's Wrong With Audio Volume Control? | Tortuga Audio
He only says he has tamed the LDR, which of course is typical audiospeak and who knows what "tamed" means.
LDR3x Passive Preamp Controller with Remote | Tortuga Audio
Here's the controller board I used.
BTW, I was reading in the Lightspeed thread yesterday, nearly all the way thru now, and I noticed that your comments there in August 2012 were nearly exactly the same as the comments you have written to me about the Tortuga. I was stunned. It was as if the units were one and the same, in design, sound, everything, which is not really so. That nearly invalidates everything you've written here. I don't think it proper to make the same comments about two dissimilar units without listening and one which you know little to nothing about, though said units are in the same general category.
Oh, and you go on and on about "mild distortion", though it used to be "low levels of low order distortion", and you couldn't then determine if it was H2 or H3, vastly dissimilar in sound.
FWIW, in my original comments on the sound, I did not mention anything about there being a tonal sound difference between the series attenuator and the Tortuga. It's the same.
Anyway that's it. I said I was out. So I'd best be out.
It's Christmas Day here in Australia now. Merry Christmas
You would be correct if the Zout of the source and Zin of the (pre)amp were both purely resistive. In practice they're not, so some device that's not a resistor might "sound better" - because it achieves a more pleasing matching between those impedances.
This may seem a bit off-topic, but maybe it's not:
Is anyone aware of any links pointing to some sort of comparison between brand-new attenuators and ones with used wipers?
The same with new VS say 3yold LDRs?
After all, IMO this sort of things mainly inspired the "invention" of the LDR attenuator
Is anyone aware of any links pointing to some sort of comparison between brand-new attenuators and ones with used wipers?
The same with new VS say 3yold LDRs?
After all, IMO this sort of things mainly inspired the "invention" of the LDR attenuator
One last post.
This pertains to the low level distortion issue. Below is a link to a dutch site with some posts a couple years ago by the designer, Mort Sissener, of Tortuga, about the distortion issue if you scroll down a bit.
Tortuga Audio LDR6 Passive Preamplifier
So you win this one DF96. Merry Christmas
However, in looking at your audio webpage I do notice that there are only tubes. You must like them.
This pertains to the low level distortion issue. Below is a link to a dutch site with some posts a couple years ago by the designer, Mort Sissener, of Tortuga, about the distortion issue if you scroll down a bit.
Tortuga Audio LDR6 Passive Preamplifier
So you win this one DF96. Merry Christmas
However, in looking at your audio webpage I do notice that there are only tubes. You must like them.
Wow.. in the best case this is first grade marketing BS, in the worst case this guy actually believes what he writes.
As we can see it requires a lot of additional electronics to control unmatched LDRs so that you get the desired attenuation and the same attenuation in the other channel.
But even if you did that perfectly there is still signal nonlinearity.
But I like the idea of auto-calibration, which of course is limited by the precision of the resistors and ADCs and DACs etc. used ...
I don't see how lines like "if you match it with component X and Y it sounds great" are good arguments for LDRs or any other specific design. First of all people also say that black plastic discs on their speakers sound great (even their wife heard it from the kitchen...) and secondly, other preamps and volume controls can be "matched" to pretty much anything else as well. And if you really want your preamp/volume control to act like an EQ then you can always add some passive components to the input or output.
I think I have read that page before. It is marketing, and contains various statements which an electronic engineer might wish to disagree with.stvnharr said:
He says:
LDRs are usually cadmium sulphide - slightly nonlinear so not too friendly to an audio signal.
He also promotes the confusion between LDRs (both a separate component and part of an optocoupler) and optocouplers (LED + LDR). An LDR is not an optocoupler! An optocoupler will contain an LED and may contain an LDR (or it may contain a photodiode or phototransistor instead).
He also says:
This is a clear attempt at FUD. It can be safely ignored.
I should not have linked to the Tortuga page and regret doing do. I think if anyone has issues with what's written there that contacting Mort directly at his email is the best resolution.
I'll post some other links for interested folks to peruse at leisure if interested.
Cadmium Sulfide, a compound in photoresistors: https://en.wikipedia.org/wiki/Cadmium_sulfide
Opto-isolators:
https://en.wikipedia.org/wiki/Opto-isolator
Optocouplers from API, the only company making LDR's: http://media.digikey.com/pdf/Data S...rs Inc PDFs/OptoCouplers Product Overview.pdf
NSL-32SR3, the LDR's used by Tortuga:
NSL-32SR3 Datasheet | DatasheetLib.com
NSL-32SR2S, the LDR's used in the Lightspeed:
http://datasheet.octopart.com/NSL-32SR2S-Silonex-datasheet-57573.pdf
We don't usually go chasing around the internet looking for other peoples' errors. There are enough on this forum to deal with. If he comes here we will put him straight, although experience tells us that when correction of misunderstanding has economic consequences the pupil can be surprisingly resistant to instruction.stvnharr said: