[time-nuts] Distribution amp - Use a video amp unit ?

[Charles P. Steinmetz]

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