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.
Where did you get these 30-50G resistors? Do they obey Ohm's Law? What's the application?
I'm interested in these for capacitor mikes.
Scott showed a graph of it a few months ago- one of those, "Geez, that's obvious!" but only in retrospect.
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DA, Digital Absortion Noise, good one, okay, back to my Maxwell equation books or whatever & the net for an explanation of that one. So, if it is square wave like, it is a problem but if it is a sine wave like, we are okay
= nuts, my ears are no good for this stuff anyways. As my dad said to me, "I don't listen to the record noise, I listen to the music"
Rick
Know not at all, but I see lots of claimed "quality cap's" encapsulated in epoxy, I wonder why that is, if it is no good? What would you suggest, that the capacitor MFG's use instead of epoxy, as an encapsulant?
DA, Digital Absortion Noise, good one, okay, back to my Maxwell equation books or whatever & the net for an explanation of that one. So, if it is square wave like, it is a problem but if it is a sine wave like, we are okay
= nuts, my ears are no good for this stuff anyways. As my dad said to me, "I don't listen to the record noise, I listen to the music"Rick
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It's an inapt analogy, marketing driven, not technical. Would you make a resistor out of Teflon? A circuit board out of zinc?
"Founded in 1969, the company’s initial products were specialized miniature chip resistors - from 1 megohm to over 1 teraohm. Still offered commercially today, these resistors are characterized by low noise and low capacitance, making them especially suitable as feedback resistors in hybrid transimpedance amplifiers (the resistors have been used to a reported 4.2 Kelvin cryogenic temperature)."
(from the Eltec Instruments website)
I used to screen the 1Tohm parts for actual resistance and excess noise at 77K. I recall one that behaved as if it had about three different paths for the current. Needless to say it was rejected.
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
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.
A Victoreen "HI-MEG" on teflon feedthroughs, 2000 megohms in this case. I actually needed it for a measurement of JFET gate leakage recently.
Attachments
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.
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.
Thanks Scott, for adding to my confusion -
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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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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