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I have a common mic preamp scheme based on ina217. Balanced part works, but I would want to add hi-z input (ub_buf), with gain control still done via ina217. ub_buf point is a buffered unbalanced input.

Can I just connect unbalanced input (ub_buf) to point (A) or point (B) directly?

I think I can't because in that case one of the ina217 input wouldn't be referenced to any particular level.

Is there a relatively simple way to connect unbalanced input, without permanently grounding one of the ina217 inputs, and without adding unbalanced-to-balanced block?

schematic

simulate this circuit – Schematic created using CircuitLab

dkiselev
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    Connecting an op-amp output directly to one of the INA217 inputs will destroy the performance benefits of the INA217. Better to make a separate unbalanced input amplifier by adding a feedback voltage divider to that TL081, then switch between its output and the INA217 output with a switch, relay, or analog switch IC. – Mark Leavitt Dec 06 '22 at 17:20

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