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Old 5th January 2011, 05:10 PM   #8501
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PMA, I know it too, but does SY? Does Jan? Does everyone else looking here? PMA, I am trying to TEACH people what the design tradeoffs are, not take credit for a specific design approach. Now, on this thread, at this time.
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Old 5th January 2011, 05:11 PM   #8502
SY is offline SY  United States
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Quote:
Originally Posted by john curl View Post
PMA, I know it too, but does SY?
Since I mentioned it a few posts back, it's a safe assumption that I do.

Read, John.
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Old 5th January 2011, 05:12 PM   #8503
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Sometimes I wonder, SY. ;-)
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Old 5th January 2011, 05:19 PM   #8504
PMA is offline PMA  Europe
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Quote:
Originally Posted by john curl View Post
PMA, I am trying to TEACH people what the design tradeoffs are,
To me, it seems to be a kindergarten lecturing sometimes. Maybe I am wrong.

I would expect 'SOTA' solutions in this thread, not elementary formula.

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Old 5th January 2011, 05:30 PM   #8505
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PMA, I am trying to give practical advice to designers, both amateur and professional. Often problem areas that I may have overlooked in my first 5 years of electronic design after finishing college (a long time ago). Perhaps, you should contribute more, and condemn less. I would certainly appreciate it, as you are a valuable resource, if you are willing to share, as I do. For the record, I rarely need to use coupling capacitors, my Parasound JC-1, JC-2, and JC-3 (just introduced) don't have them.
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Old 5th January 2011, 05:42 PM   #8506
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Now, let us 'creep forward' to understand what happens when you use a smallish cap. like .033uF, as in our last example, with a 1 meg resistor.
Now, the 1 meg resistor makes its own noise, and this must be shunted out by the coupling cap, if possible. If not, then the FULL 1 meg noise will be amplified by the next stage. Determining how well the .033 uF cap does this, takes a bit of figuring. (more later)
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Old 5th January 2011, 06:02 PM   #8507
tvi is offline tvi  Australia
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I avoid "audiophile" caps because of microphonics, quality control, and reliability
Show some tests or at least list the ones you have tried so we can all avoid them, it would be common courtesy of you not to horde such potentially usefull information?


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Old 5th January 2011, 06:15 PM   #8508
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Show some tests or at least list the ones you have tried so we can all avoid them, it would be common courtesy of you not to horde such potentially usefull information?
My tests were putting the cap into an RC coupling circuit at the input to my preamp and tapping them with a pencil looking at the output on a scope or listening through headphones or speakers. I've experienced, but did not quantify, the opposite effect- sound generation by electrostriction. Anyone can do these tests for themselves.

Over the years, people have gifted me with all sorts of "fancy" caps to try; I admittedly haven't kept systematic records since they either performed poorly, performed no better than conventional cheap caps, or were so out of spec from the get-go that it wasn't even worth trying them; they just get chucked into my "dodgy parts" box and gather dust. Since this is something that I personally don't find terribly interesting or important, I'm reluctant to name names without having systematic, well-documented records in case anyone's lawyer is feeling frisky. Sorry to disappoint. I will and have named names of conventional inexpensive caps that I've found to work as well as anything else out there.
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Old 5th January 2011, 07:08 PM   #8509
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My previous example using SY's criterion of 1 meg and .033uf did NOT come to any real noise problems, IF the cap was REALLY an interstage cap. Perhaps 5nV/rt Hz at 100 Hz, not too bad, but I have thought of another interesting example, one that many here might just try, if they were so inclined. (more later)
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Old 5th January 2011, 07:41 PM   #8510
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Quote:
Originally Posted by john curl View Post
My previous example using SY's criterion of 1 meg and .033uf did NOT come to any real noise problems, IF the cap was REALLY an interstage cap. Perhaps 5nV/rt Hz at 100 Hz, not too bad, but I have thought of another interesting example, one that many here might just try, if they were so inclined. (more later)
Although thermal noise might not be such a big problem with high impedances in interstage coupling, high impedances make the circuits much more susceptible to noise pickup of different kinds.
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