[sdiy] Better testing techiques for audio circuits

[Neil Johnson]

Hi Tom,

> Could you use a oscilloscope's "difference" function for this job? I often have one channel connected to input, and one to output. "difference" would be the stuff the circuit adds.
> Or is a voltmeter better for some reason?

Two reasons:

1/ If the circuit under test adds any phase shifts (very likely) then
you will never get the two to cancel out algebraically.

2/ Unless the distortion is huge you just won't see it on a scope.
Also, unless its a fancy digital one you won't be reading RMS volts.
And its the "RMS" which is the important bit.

Cheers,
Neil
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