My version of the G = 1000 low noise measurement amp (for Ikoflexer)

If you still want any good discrete analogue devices, this year is probably your last chance to buy lifetime stock.

No one is really doing well with analogue discretes.
NXP is sold / split, so discretes like BF862 are now Chinese.
Toshiba Semicon is most likely to be sold soon, and who knows what the new owner would do.
Fairchild is now On-Semi, so is Sanyo Semi, .....

The list keeps growing.


P.
 
The Wurcer LNA for P-JFETs is working.
Input signal was 1mV sine.

More tests to come (noise measurements, etc.)


Patrick

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The Wurcer LNA for P-JFETs is working.
Input signal was 1mV sine.

More tests to come (noise measurements, etc.)


Patrick

.

Good and good luck finding new choices. Even some batches of J310's were not too bad for some applications but nothing P made over the years by usual suspects ever was very good. Those P-channel switches National? made were OK but an unusual exception.
 
How about the PJFETs in the input stage of the TL072? Could a large area, basket weave layout on that fabrication process, give a low noise discrete if they wanted to try?

Already did, gm/C figure of merit is not that good (50pF Cin for a 2.9nV diff-pair). On some of the new SOI processes things are better but no one is going to make discreet P FET's for fetish style design philosophies. Complimentary symmetry just sounds better, etc.
 
Not the neatest setup. Performance in this breadboarded version is flat from 50Hz to 200kHz @60dB, but rises to a peak of 61.5dB ~16Hz. Note the ultra precise probing technique:

Ummmm... this could be "by design". I can't find the exact schematic, but the original Mr. Wurcer design in #1 appears to have 2 poles at LF, one is C2R6 the other is C5-whatever gives the optocoupler (no idea how the freq response and impedance looks like). If these two poles happen to be close in frequency, when you close the loop the LF response may overshoot. You need a zero to compensate the second pole, a resistor in series with C2 will do.

P.S. The closer the poles are, the higher the overshoot. 1.5dB as reported is not that bad, you can leave it as it is and happily live ever after.
 
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