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Old 8th August 2014, 01:50 PM   #11
SY is offline SY  United States
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Quote:
Originally Posted by Conrad Hoffman View Post
I think I mentioned that, as mica caps are the example always used for very low DF with surprisingly high DA. It's true, but that "high" DA is in comparison with better dielectrics and my guess is it isn't even on the map compared to the stuff they make cables out of, with the exception of Teflon.
If memory serves (I don't have my tables with me), the worse DA among polymers is from PVC, and it's still 5 times lower than mica. That is going off memory, though, and I'm old.
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Old 8th August 2014, 01:51 PM   #12
BigE is offline BigE  Canada
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Hi Conrad,

Have you tried using audiodiffmaker?
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Old 8th August 2014, 01:55 PM   #13
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Quote:
Originally Posted by Conrad Hoffman View Post
Remember, no edge here! The input signal is a 2 kHz triangle wave, not square, and the edges you see on the scope are the result of the triangle switching direction. The droop is a relatively slow thing in comparison.

I know for certain my ears are not golden and I don't know about hearing .08% of anything (there's no 24Vpp, the input is 12Vpp), so it either gets much worse at higher frequencies or I'm not looking at the math right. I may not be choosing the cutoff point of the droop correctly on the relatively fuzzy scope image.
I tend to believe that whatever changes to the signal you cannot hear are multiplied by whatever other chances you cannot hear in every other component in your system to the point where you hear a definite change from what you /should/ be hearing.

Everyone knows what a Trumpet sounds like. now put that through a hundred components and then try to make it sound the same.

https://www.youtube.com/watch?v=d70fiI2Mn_A
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Last edited by freax; 8th August 2014 at 01:59 PM.
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Old 8th August 2014, 02:02 PM   #14
udok is offline udok  Austria
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You are right! At the moment i saw only the scope pictures with the rectangle...
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Old 8th August 2014, 02:02 PM   #15
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Originally Posted by BigE View Post
Hi Conrad,

Have you tried using audiodiffmaker?
I've fooled with that in the past and don't remember much, but it's a very good idea. This is stuff that really needs to be crosschecked using different methods.

BTW, anybody with a scope can, and should, duplicate this test. Almost all two channel scopes will let you invert one channel and then sum them (A+B mode), giving you a differential amplifier. Find a couple matched resistors, a function generator and Bob's your uncle. You won't have the gain available on my diff plug-in, but the signals here should be quite visible with normal 5 mV/div settings.
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Old 8th August 2014, 02:04 PM   #16
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I'm curious how Teflon will perform in your tests, will you acquire any? I could send you a piece for free.
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Old 8th August 2014, 02:26 PM   #17
jcx is online now jcx  United States
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yes, use any polymer film dielectric before Mica https://web.archive.org/web/20051226...570,28,00.html
and some rambling What's all this soakage stuff, anyhow? | Analog content from Electronic Design
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Old 8th August 2014, 02:39 PM   #18
AndrewT is offline AndrewT  Scotland
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Yes, the triangle to square is a bit of a handy trick. The best way to see it is to draw two triangle waves
does that mean the output is in effect a measure of the phase shift?
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Old 8th August 2014, 02:47 PM   #19
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does that mean the output is in effect a measure of the phase shift?
Yes, but not in the usual AC sine wave sense. Think more in terms of charging the cap with constant dV/dT (triangle) through a resistor, rather than a sine function.

Kastor- yes, I tested some Teflon aircraft coax. Fantastic stuff on the waveform, also has a dissipation factor of 0.00002, though moderately high capacitance.
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Old 8th August 2014, 02:55 PM   #20
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I have to reread Pease, but actually don't agree with never using mica. I've used it in RIAA sections with no sonic problems I could detect. Mylar is a far worse performer for distortion and I avoid it when possible.

An interesting thing about mica caps is that I've never heard of them being a problem in any AC circuit, only with slow speed stuff like integrators. Interesting that they also look good in my test. Does anybody know anything about dielectric absorption frequency ranges? Does performance in a 1 second test predict high frequency behavior? This seems like stuff we need to know to predict audio performance. Later today I'll try to run some traditional DA tests on the same cables.

Now, I think it's Rod Elliott that makes a good argument for dielectric absorption not being audible or a factor in audio. I respect him greatly and he makes a good argument, but I also think circuit locations and impedances are everything when it comes to what's important.
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