Usually instruments that are named VOMs cannot measure low enough AC voltages to give good results.

The circuit I described above had AC outputs in the tens of millivolts. It seems a voltmeter that could read that would have to be a couple hundred bucks. The input to the circuit is the output of an amp with ten volts of output. This would be the voltage level of 12.5 watts into 8 ohms. While that's not a huge wattage, it's way more than the average portable amplifier source would output.