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Old 11th October 2012, 08:01 PM   #28111
SY is offline SY  United States
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Originally Posted by PMA View Post
Would you kindly teach us? Any measurements to support your claim?
I can't go into formulation, that would (as has) taken many books to fill, but the main points are that you can easily make a panel (or enclosure) that has a conductivity gradient chosen to maximize EM absorption. Likewise, you can make a material with a very high loss factor or one with novel magnetic properties. The literature is full of measurements, my own were done back in the '80s; some of my patents from Lockheed should give you more than a hint.

These days, I don't design equipment that needs heroic measures to function properly.
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Old 11th October 2012, 08:08 PM   #28112
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they were special order from one of the resistor companies, glass encapsulated, silicone coating to make them hydophobic on the outside, the tempco wasnt great. They were used for a flame ionization detector that counts carbon atoms going through a flame.

Wrinkle
A Victoreen "HI-MEG" on teflon feedthroughs, 2000 megohms in this case. I actually needed it for a measurement of JFET gate leakage recently.
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Old 11th October 2012, 08:10 PM   #28113
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Originally Posted by bcarso View Post
And indeed, that's how the hook problem was noted. I would love to find that reference.

I think it was Tektronix who had come up with some integrated circuits for the vertical amplifier chain --- was it for the 485, or one of the mainframe 7000 series scopes? --- and used some PCB pads for low-value capacitors as part of the matching networks to the chips.

I should ask John Addis if he recalls that article, as I believe he was there at the time.
Long before that trimmers were made of thin enamel insulated wires wound around thicker wires. I saw that in Soviet radio receivers designed in 1950'th.
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Old 11th October 2012, 08:21 PM   #28114
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The 'best' caps generally do not use epoxy as an outside coating. AND they certainly don't use epoxy for the cap dielectric material. However, a circuit board is a number of small caps that are created by the board material and the spacing between conductors. That is why SY recommends Teflon standoffs, when he considers them necessary (I do too). Taking things to the ultimate, Teflon boards are 'better' than FR-4 boards, just like carbon fiber might be a 'better' material for a race car than steel.
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Old 11th October 2012, 08:26 PM   #28115
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Thanks Scott, for adding to my confusion - Sorry to ask, what is "DA" noise?, boy, do I have a lot to learn and their is only so much time left!! Cheers Rick
I was not totally kidding, like Tek if you make capacitors out of FR4 they have horrible dielectric absorption which acts as a loss resistance which does have noise in a high impedance circuit. I easily measured it in a mica cap which is actually supposed to be a cap. Those Tek guys probably thought they were very clever.
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Old 11th October 2012, 08:29 PM   #28116
bcarso is offline bcarso  United States
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Long before that trimmers were made of thin enamel insulated wires wound around thicker wires. I saw that in Soviet radio receivers designed in 1950'th.
Around here those used to be called "gimmicks".
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Old 11th October 2012, 10:35 PM   #28117
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Originally Posted by john curl View Post
Taking things to the ultimate, Teflon boards are 'better' than FR-4 boards, just like carbon fiber might be a 'better' material for a race car than steel.
Problem is, when it comes to actual performance for this application, it's not better. Either it's unfilled, in which case it's mechanically floppy and cold-flows easily (nice to have a flexible, rattly board in a soundfield?), or it's glass filled and the bulk dielectric properties are dominated by the glass as is the case for glass epoxy composite. In both cases, the trace integrity is markedly degraded compared to glass epoxy, reducing reliability.

Teflon PCB is a good choice for some very specialized applications, but audio isn't one of them- except for the fashion and hype factor, of course. The faith-based audiophile pays more and gets poorer performance and reliability.

edit: If you want to have your cake and eat it too, you could do point to point between standoffs (silver wire, natch!) so that the dielectrics are dominated by Teflon and air. As your Parasound demonstrates, you don't really get any performance advantage by avoiding reliable glass epoxy, but it IS a high coolness factor.
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Old 11th October 2012, 10:54 PM   #28118
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Originally Posted by bcarso View Post
A Victoreen "HI-MEG" on teflon feedthroughs, 2000 megohms in this case. I actually needed it for a measurement of JFET gate leakage recently.
Wash your hands!
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Old 11th October 2012, 10:56 PM   #28119
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Originally Posted by SY View Post

Teflon PCB is a good choice for some very specialized applications, but audio isn't one of them- except for the fashion and hype factor, of course. The faith-based audiophile pays more and gets poorer performance and reliability.
Unless Teflon PCBs have actual audible benefits.
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Old 11th October 2012, 10:58 PM   #28120
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You might have a point, SY, I will check further.
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