John Curl's Blowtorch preamplifier part II - Page 2811 - diyAudio
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Old 11th October 2012, 07:30 PM   #28101
bcarso is offline bcarso  United States
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Originally Posted by john curl View Post
rsavas, would you make a quality cap with FR-4? That is the answer to your question.
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.
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Old 11th October 2012, 07:34 PM   #28102
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Originally Posted by wrinkle View Post
Bingo, I needed those for a circuit with 30-50G feedback resistors, but even so the board needed to be spotless.
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.
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Old 11th October 2012, 07:35 PM   #28103
SY is offline SY  United States
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Originally Posted by Wavebourn View Post
Digital Absorption noise? It should sound like sucking of numbers.

Can't imagine how it sounds...
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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Old 11th October 2012, 07:36 PM   #28104
rsavas is offline rsavas  Canada
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"
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rsavas, would you make a quality cap with FR-4? That is the answer to your question.
"
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

Last edited by rsavas; 11th October 2012 at 07:49 PM.
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Old 11th October 2012, 07:39 PM   #28105
SY is offline SY  United States
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Originally Posted by PMA View Post
So why are you thinking of conductive plastics now? Horrible compromise.
If you know how to formulate and handle these materials, they can do EM tricks that metals can't.
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Old 11th October 2012, 07:40 PM   #28106
SY is offline SY  United States
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Originally Posted by rsavas View Post
"
Know not at all, but I see lots of claimed "quality cap's" encapsulated in epoxy, I wonder why that is, if it no good? What would you suggest, that the capacitor MFG's use instead of epoxy, as an encapsulant?
It's an inapt analogy, marketing driven, not technical. Would you make a resistor out of Teflon? A circuit board out of zinc?
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Old 11th October 2012, 07:54 PM   #28107
bcarso is offline bcarso  United States
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Originally Posted by kgrlee View Post
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.
"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.
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Old 11th October 2012, 07:54 PM   #28108
PMA is offline PMA  Europe
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Originally Posted by SY View Post
If you know how to formulate and handle these materials, they can do EM tricks that metals can't.
Would you kindly teach us? Any measurements to support your claim?
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Old 11th October 2012, 07:55 PM   #28109
rsavas is offline rsavas  Canada
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Would you make a resistor out of Teflon? A circuit board out of zinc?
Sure would, if I could find a sucker to buy them and only for that reason alone!! Not really, I am not like that!! I'd tell him the truth, to be honest. I hate people taking advantage of others.

Last edited by rsavas; 11th October 2012 at 08:00 PM.
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Old 11th October 2012, 07:55 PM   #28110
wrinkle is offline wrinkle  United Kingdom
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Originally Posted by kgrlee View Post
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.
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
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