[sdiy] Better testing techiques for audio circuits

[Tom Wiltshire]

On 3 Apr 2012, at 10:42, Justin Owen wrote:

> Thanks for everyone's input on this - some really good info, much appreciated.
> 
> Neil - can I just clarify...
> 
>> 1/ The nulling technique, where you apply a stimulus (e.g., a sine
> wave) to a circuit and then measure the difference between the input
> and output using a true RMS AC voltmeter.
> 
> I'm measuring the stimulus at source (a) - e.g. a sine wave generator at its output, not connected to anything (except the meter), then I'm taking a second measurement at the output of the circuit under test (b) with the sine wave as an input to that circuit and from there I can assume that the difference between (a) and (b) is 'stuff' (noise?) that's introduced by the circuit?
> 
> How much more detail can I potentially get out of that other than e.g. seeing that a 5V AC input is coming out at 5.2V and therefore the circuit is adding 0.2V of 'stuff'? Does that make sense?
> 
> Thanks,
> 
> Justin


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?

T.