[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.
Ed
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