[sdiy] High impedance measurement buffer for audio?

[Mike Bryant]

Wouldn't a high voltage op-amp in unity gain mode with a floating power supply fit the bill ?
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From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Mattias Rickardsson via Synth-diy <synth-diy at synth-diy.org>
Sent: 26 October 2026 09:04
To: Synth DIY <synth-diy at synth-diy.org>
Subject: [sdiy] High impedance measurement buffer for audio?

Hi all,

I often probe around in both audio circuits, power circuits and other circuits. I often want to direct the probed signal both to an audio interface and to measurement equipments like oscilloscopes. But when the test point is sensitive, I don't want to load it and affect the signal.

Do you have any good recommendations for a device solving these needs:

- High impedance measurement input for a +/- 20V range
- Buffered outputs to both audio & lab equipment simultaneously
- No gain needed
- Very low noise and low THD needed, it shouldn't degrade the signal before going to my high-end audio interface
- High bandwidth preferred, far higher than audio

Could be a commercial product or a custom-built solution. Are you aware of any obvious solution that I've missed? Or is the low-noise low-THD requirement a tricky thing here? :-)

/mr
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