[volt-nuts] 731A output impedance

ed breya eb at telight.com
Wed Nov 28 15:55:20 UTC 2012

If you do modify the circuit, you will probably want to decrease the 
series R. Even though the external loads are likely to be in the 
megohm range, the feedback load is significant, and likely the 
biggest part, except for fault conditions. For lowest noise and 
suppression of effects due to bias current, the DC feedback network 
needs to be low in resistance, so 1k in series may add too much drop 
and make the amplifier run out of headroom, or change the amount of 
self-heating in the amplifier die, affecting it in unpredictable ways.

If you use series R in the 100 ohm range, it should have less effect 
on the normal amplifier conditions, and still provide some degree of 
fault isolation. You can add clamp diodes if it doesn't have them 
already. For 10 V output, I'd recommend a 12 V, 1W zener to ground 
right on the amplifier output, and a diode to the plus supply.


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