[sdiy] High impedance measurement buffer for audio?

[Roman Sowa]

Good active probe might cost more than the oscilloscope itself, even 10x 
more if the oscilloscope in question is for example a Rigol.
That's why I made poor-man's version, using Analog Devices old AD8001 
opamp with 1GHz bandwidth as voltage follower. Output pumping regular 50 
ohm cable to the oscilloscope. I have a picture somewhere, but nothing 
to be proud of. It's all dead spider technique directly on opamps leads. 
It was THT package so it was pretty easy.

You can do exactly the same, and since it's for audio, why not use 
something like OPA1641. To achieve +/-20V input range add 1:2 input 
divider with 1M resistors and compensating trim-caps

Roman

W dniu 2026-10-26 o 10:04, Mattias Rickardsson via Synth-diy pisze:
> 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
> 
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy at synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org