Audio Signal Monitoring for Short Circuit Detection

Thread Starter


Joined Nov 29, 2013
Polling the forum for opinions and advice about the feasibility of the attached circuit for input and output monitoring of an audio amplifier.. Theory being ideally both inputs to the op amp identical until some condition at the limits or shorting of the audio amp output..
Thanks for any ideas thoughts



Joined Jun 4, 2014
The two signals will not be exactly the same if only because the amplifier frequency response will not be completely flat so at some frequencies the two signals will be different. To get reliable results I think you will need to bandpass both signals to a broad band in the middle of the audio band. Then rectify them to get two DC signals and then feed them to a window comparator so there is a difference in level which is acceptable but bigger differences will trigger the signal.


Joined Nov 30, 2010
There is a lot wrong with that circuit. First, it depends on the speaker voltage level being EXACTLY 11.000 times the input signal voltage. Any use of the volume control or the tone controls causes instant fail. U1 is designed with a gain of about 100,000, so a millivolt of difference is more than enough to cause a rail-to-rail output. After a mistake like that, the rest of the circuit isn't worth evaluating because it will not receive any useful information.

I wouldn't even try to fix that circuit. Start over.