Bruce wrote:
The above reverse isolation [~35 dB] is about 25dB lower than I would expect.
D'oh! Bruce is right -- I calculated the reverse isolation incorrectly. I had only been expecting 40 dB, so I didn't question the result. The breadboard actually measured nearly 63 dB.
Stable operation at unity gain is necessary if a feedback capacitor is used.
The Miller capacitance of the output transistors sees to that (with an even greater phase margin when a faster transistor is used for Q1).
An LM329 has similar noise without the dissipation of the internal heater in the LM399
I know. I just particularly like the 399, and have a pile of them. I rationalize using it in this case by noting that the range of frequencies where phase noise of the DA is important includes sub- to low-Hz frequencies at which thermal effects could make the unheated 329 significantly noisier (though if you keep drafts off both of them, it might not be by a large amount).
Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
