Attaching a scope to the Zone 2 output would be the best diagnostic tool. Protection circuits are usually designed to detect over current and DC offset transgressions, but they can sometimes detect clipping (voltage limit). A DC voltmeter can be used to check for simple DC offset, but a simultaneous AC signal will probably frustrate the voltmeter. Due to typical voltmeter frequency response and waveform limits, it will be of marginal use to prove or disprove clipping. One indication would be that the voltmeter reading stops increasing as the amplifier input voltage is increased, but using the amplifier's Volume control to set the amplifier input voltage will be difficult to deal with because the control taper is not likely to be linear.

I would be tempted to build or buy a gadget similar to this.

Maybe for diagnosis at low power levels but those typically have a pretty low power input capacity.

Most volume controls are audio taper, IIRC.

The audio taper controls just add a little confusion for the human who might expect the taper to be linear. 70% rotation is not 70% of rated output -- especially since we don't know the input voltage. (it could be zero if the input is silent)  It's still just a voltage divider.

Those little "boxes" are simple voltage dividers. It's easy enough to design your own. There are two issues that can bite. First, calculate the power dissipation of the resistors at the full power speaker terminal output voltage, then keep the values low enough that cable capacitance will not roll off the highs, but high enough that you won't burn up the little box or pill capsule that you are using to house the network.

If you are super worried about high frequency roll off, include a little buffer amplifier with a very short wire to the divider network.

Yes. Definitely.

If you set up a linear taper pot as a volume control, you'll be surprised that you seem to be at more than 50%* up in volume with only 10% rotation* of the pot (or vice versa). This is because, like most things biological, our senses do not respond linearly, but in a more nearly logarithmic (or antilogarithmic) way.

Sooner or later someone was going to ask why. I thought I'd shorten the discussion.





*more or less

Most people don't know the difference between audio vs linear taper, anyway.

I have used many high-low level converters when I did car audio but those were maybe 15W/channel and even then, some of them burned up. The issue is usually in the power rating of the resistors and how the heat is dissipated, as well as how long it's receiving the signal at that level.