I am missing something as the audio out of the amp will be a varying waveform going above and below 0 at some frequency. Meaning it will not remain above 15 volts but be constantly changing.
I am missing something as the audio out of the amp will be a varying waveform going above and below 0 at some frequency. Meaning it will not remain above 15 volts but be constantly changing.
Attached is your circuit with and without the cap. The only way this will work with audio is maybe divide down the voltage and run it into a comparator that drives a retriggerable one shot with a time constant longer than the lowest frequency you expect to see. That would be my guess anyway.
Public address systems usually use high voltages to distribute audio over distances of hundreds of feet. Transformers at each speaker drop the voltage down to voice coil level. The transformers usually have different primary taps to adjust the amount of power used by each speaker.
70 volt systems are very common. But 70 volts is the nominal voltage. Depending on the actual audio level, the measured voltage may be different. Also, unless the multimeter is of the true RMS variety, the measurement is likely accurate only if the signal is a sine wave.
Read this link about comparators. Make a voltage divider circuit of about 10:1 off the bridge posted earlier. Then drive a retriggerable one shot off the comparator setting the time constant for about a second or anything as mentioned earlier. Longer than the lowest frequency you expect to see. I posted a sim of what your circuit outputs would look like with and without the capacitor.