If anyone sees a theoretical issue with my schem I'd be grateful
for any enlightenment.
If the schem is OK then I guess I'll find it through regular
troubleshooting procedures.
Actually I'm getting readings all over the place.
Part of the problem seems to be that I'm testing the board out of
context, as a bare board with a 100pF cap in place of the capsule.
Anything disturbing the input seems to result in massive changes
to the virtual ground voltage. I'm not sure why this would so
massively affect the DC operating point.
Removing the opamp is not an option as it's a surface mounted one
and not socketed. The transformer isn't much easier.
I now think it probably isn't the transformer at issue.
On 30/04/2025 21:18, kennjava wrote:
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How far off-center is the virtual ground voltage?
?
I would try disconnecting stuff:
1) remove the opamp and measure voltages (all voltages)
2) restore the opamp, measure again?
3) disconnect the transformer, measure again,
4) disconnect the mic element, measure again
?
etc. The idea is to try to find what's creating the imbalance
