John Curl's Blowtorch preamplifier part II - Page 2422 - diyAudio
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Old 6th July 2012, 03:01 AM   #24211
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Thanks Dick, for your input. Apparently, Scott has changed his view on what is important in caps, over the decades.
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Old 6th July 2012, 03:15 AM   #24212
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> and by many amateurs today
and even some professionals .............
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Old 6th July 2012, 04:04 AM   #24213
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Well, ever onward! IF people think that high value ceramics or electrolytic caps are A-ok for their audio projects, then go to it. Yet, it is not impractical to use better parts, or no coupling caps at all. All you have to do is to add servos. Are servos a perfect solution? No, it is possible that they can contribute something to the sound IF they are made with distinctly non-linear components, and their bandwidth (operating range) comes too close to the audio bandwidth. It is best to never use a servo for a high pass filter. I have tried it, and failed. You probably will too. This is because the servo is WORKING along with the audio and adding to it, rather than JUST CONTROLLING the DC offset. If you ever have a servo and you can see AC rapidly changing across it, you are too high and you have to lower your time constant (RC) that is usually 1 meg and 1uF making a RC time constant of 1. This seems to work almost always. Don't try to compromise, it is fairly easy to do, at a reasonable price and in a reasonable space. I have found Mylar caps to work OK, but don't use anything much cheaper.
Now, some here will NOT use servos, and they may be on to something. I have seen DC coupled power amps and preamps made with very close matching over temperature, and they do NOT need a servo, but at what price? A very high price in time and effort, and that is why I use servos in almost all my designs, including the CTC Blowtorch. Works for me!
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Old 6th July 2012, 04:30 AM   #24214
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> If you ever have a servo and you can see AC rapidly changing across it,
> you are too high

Ya Mon ...... Instant active DA ........

Last edited by hitsware; 6th July 2012 at 04:32 AM.
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Old 6th July 2012, 04:39 AM   #24215
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Have you ever been 'high' hitsware? Have you ever designed a servo? What is your solution to the problem?
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Old 6th July 2012, 06:14 AM   #24216
Bonsai is offline Bonsai  Taiwan
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"A linear time invariant system that shows second harmonic distortion from a synthesized waveform but not sine waves is an extraordinary result."

The AP shows no distortion from a suitably sized electrolytic cap. That said, I think some caps are very bad news and I wrote a few comments about my experiences in my e-Amp article - e.g. singing ceramics on one of the prototypes.

If you follow the good advice about sizing electrolytics correctly (from Cyril Bateman), avoid using ceramics (other than NPO/COG) in audio, steer clear of polyester and mylar and one or two others (from Dick Marsh and Walt Jung's article) you should be ok.

Hell, I just realized that doesn't leave much choice ;-)
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Old 6th July 2012, 06:30 AM   #24217
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Those who measure harmonics ONLY will not find much, except in tantalum and ceramic.
DA does NOT measure like distortion, but it is a deviation from the IDEAL waveform that is normally expected from simple models. However, apparently virtually every electrolytic cap has SOME distortion, if you look hard enough, over a broad range of frequencies.
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Old 6th July 2012, 12:32 PM   #24218
Bonsai is offline Bonsai  Taiwan
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Maybe the question as to the effect electrolytics have on sound quality should be posed differently, if we cannot measure distortion through them.

What audible changes are possible that might alter the perceived sound quality that would not be detectable using the usual THD test?

Let's exclude frequency response on the assumption that the cap value is chosen such that these effects lie well beyond hearing limits, say 3 octaves or more.
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Old 6th July 2012, 01:07 PM   #24219
DF96 is offline DF96  England
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Quote:
Originally Posted by john curl
DA does NOT measure like distortion, but it is a deviation from the IDEAL waveform that is normally expected from simple models.
It is good that DA does not measure like distortion, because it is not distortion. Which "ideal" waveform? The one assuming that all capacitors are just that: perfect capacitors? Who "expects" that?

If DA really can be heard, then that means that we are sensitive to very tiny deviations in frequency response. If DA apparently produces second harmonic from any waveform then there is a problem with either the measurements or their interpretation as DA cannot do this. Far more likely that DA is a marker for some other dielectric problem. Can we look for that, and stop all this nonsense about DA itself?
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Old 6th July 2012, 02:11 PM   #24220
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Quote:
Originally Posted by DF96 View Post
If DA really can be heard, then that means that we are sensitive to very tiny deviations in frequency response.
Without specific reference to DA, my own (non-scientific) experiments have led me to conclude that very small, but broadband, frequency and/or timing (phase and impulse) responses are indeed audible. It seeems as though the information correlation between the channels is instrumental in revealing such very small response variations. Okay, I'm going to open myself to ridicule, because likely few will believe the following anecdotal report. I could hardly believe it myself. I recently was experimenting with electrically mixing minute amounts of crosstalk (don't ask why ) between the stereo channels. By minute, I mean, a ratio of crossfeed at around -110dB. Not only could I hear an effect at that level, but the effect was was immediately obvious. What was more disconcerting is that I could also hear small changes in the crossfeed around that -110dB level.

Because of that experience, I've come to suspect that, perhaps, the differences some of us hear in cables and interconnects, and various 'voodoo' tweaks, stem from minute alterations in system frequency and/or timing response.
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Last edited by Ken Newton; 6th July 2012 at 02:20 PM.
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