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Re: new polymer caps

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Am 05.09.25 um 17:12 schrieb john larkin:
> On Thu, 4 Sep 2025 20:13:42 +0200, Gerhard Hoffmann <dk4xp@arcor.de>

> Did you find that the polymers created noise?

They did in my circuit. One comparison may not be statistically
significant for the general case, but enough to think about
if there should be problems.

It seems the circuit is a magnifying glass.
16 CPH3910 in parallel for a *low* noise preamp (315 pV/rtHz),
gate at GND, sources fed from a current mirror CCS, cascode,
output amplifier in 10 dB steps to +80 dB.

There was no 1/f corner but 1/f**2 and that gets out of hand
quite fast. 40 dB/decade. Maybe a less ideal CCS would have
helped. Anyway, the effect wandered clearly with capacitor
type over 3 or 4 decades of noise corner frequency.
Just keep it in the back of your mind.

Evading the feedback somehow felt like a personal defeat
so I took a bit more gain from the cascode and replaced
the op amp by a BFS19S follower to drive the low impedance
sources. Burns some precious battery power. But it seems
to be fast enough and avoids the 1/f noise of the 3 GHz CFA.

BFS19 is EOL as Digikey wrote me last week.  :-(

cheers, Gerhard

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new polymer  caps john larkin <jl@glen--canyon.com> - 2025-09-04 10:26 -0700
  Re: new polymer  caps "Edward Rawde" <invalid@invalid.invalid> - 2025-09-04 13:58 -0400
    Re: new polymer caps John R Walliker <jrwalliker@gmail.com> - 2025-09-04 19:15 +0100
      Re: new polymer caps John Robertson <jrr@flippers.com> - 2025-09-04 13:26 -0700
        Re: new polymer caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2025-09-05 08:43 +0100
          Re: new polymer caps Joe Gwinn <joegwinn@comcast.net> - 2025-09-05 08:42 -0400
            Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-05 23:24 +1000
              Re: new polymer caps Jeff Layman <Jeff@invalid.invalid> - 2025-09-06 08:19 +0100
                Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-06 18:15 +1000
                Re: new polymer caps JM <sunaecoNoChoppedPork@gmail.com> - 2025-09-06 20:18 +0100
                Re: new polymer caps Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2025-09-06 17:46 +0000
                Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-07 14:38 +1000
        Re: new polymer caps john larkin <jl@glen--canyon.com> - 2025-09-05 08:01 -0700
  Re: new polymer caps Gerhard Hoffmann <dk4xp@arcor.de> - 2025-09-04 20:13 +0200
    Re: new polymer caps Gerhard Hoffmann <dk4xp@arcor.de> - 2025-09-04 20:25 +0200
      Re: new polymer caps Jeroen Belleman <jeroen@nospam.please> - 2025-09-05 00:14 +0200
    Re: new polymer caps john larkin <jl@glen--canyon.com> - 2025-09-05 08:12 -0700
      Re: new polymer caps Gerhard Hoffmann <dk4xp@arcor.de> - 2025-09-05 19:23 +0200
        Re: new polymer caps john larkin <jl@glen--canyon.com> - 2025-09-05 13:53 -0700
          Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-07 02:35 +1000

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