[volt-nuts] 731A output impedance

WB6BNQ wb6bnq at cox.net
Tue Nov 27 22:33:16 UTC 2012

Hi Ed,

I am a little confused with regard to your paragraphs 3 & 4.  Could you elaborate
on those two paragraphs ?

thank you,


ed breya wrote:

> The simplest way to drop the output impedance without adding much
> circuitry is to just change the series R to 100 ohms or so - that
> would still give pretty good isolation from capacitive loading.
> If the R is dropped to zero, the DC performance will be best, but
> you'll have to worry about the amount of capacitive loading. If the
> lines are short - say a couple of meters or less of open wire, it
> would probably be OK, but that much coaxial cable may make it oscillate.
> The suggestion to get the feedback right from the output terminal,or
> even with external sensing at the load would be best for DC accuracy,
> but would have the same problems as above.
> You can also take the DC feedback from the output directly, and the
> AC feedback from the amplifier output, while the series resistor
> isolates the two. This would give good DC accuracy and AC stability,
> but would alter the dynamic response and LF noise shape somewhat.
> If you add an amplifier, you'll of course have to consider its offset
> and noise contribution, and it will have the same stability issues to resolve.
> Ed
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