Differential vs Single Ended

I’m building a voltage divider for use in testing high power amplifiers with the QA402. It seems there is a choice when feeding the signal from the divider into the QA402. I can use the amplifier ground and feed the QA402 single ended or I can pick up the signal from either side of one of the dropping resistors and feed the QA402 a differential signal (leaving the grounds disconnected).

Is one better than the other? Sorry if this duplicate previous questions, I’ve searched around and can’t find anything.


If you use differential then any difference between amplifier input and output grounds won’t cause abnormal currents to flow round the ground system - think about speakers - they get a differential signal defined relative to the output ground, and thus so should your measurements…

You could try both and see if there’s differences in the results of course…


A lot of amplifiers these days, especially in the professional realm, are self-bridged outputs. In other words both sides are driven. You have no choice but to use differential inputs for these. Also some have the negative (black) terminal driven with Inverted polarity, and the red + terminal grounded on every second channel. You really need to suss this out with a voltmeter before connecting any expensive test gear to an amplifier. Remember, a loudspeaker is a floating balanced input. Your measurement should be as close to that as you can get.

I built some test cables and adapter boxes and posted about them here:

Dale Shirk

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