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Audio Hardware / Re: Continuously monitor Power Amp Input or Output to see if it is maxing out
Last post by DVDdoug -Quote
I am thinking of a gadget designed for the job, or maybe of making something based on a USB ADC with some sort of software, or a multi-meter that continuously monitors a signal,There is a circuit called a peak detector, which at its simplest is a diode and a capacitor. The capacitor charges-up to the peak voltage and the diode prevents it from discharging. You can measure the DC voltage and calculate peak power. Or, once you know the approximate maximum voltage you can get, you can just monitor and mentally compare with the maximum.
As you may know, there is a ~0.7V drop across the diode, and the RMS is 0.707 times the peak. So make those adjustments when calculating power. Or if you make a full-wave version, that's a ~1.4V drop.
When testing for the maximum, don't run continuous test-tones or you might burn-out the woofer! (Run quick bursts.)
I actually ordered some parts to build one (in a box with banana jacks, etc.) but I haven't started it yet. I added 2 resistors - A ~10 Ohm resistor in series with the diode limits the current so the capacitor doesn't "short out" the amplifier when charging. And a high-value resistor in parallel with the capacitor to slowly discharge it (depending on the RC time constant). I think I ordered a 5W, 10 Ohm resistor. It doesn't have to handle the full amplifier power because current only flows when the capacitor is charging. (I didn't do any "real calculations".)
I apologize for describing a circuit with words... I might have a schematic on another computer and If I can find it later, I'll see if I can attach it.
You can also make an Active Peak Detector with an op-amp, and the diode drop is automatically compensated for by the feedback. (Of course you need a power supply, and a voltage divider and maybe some over-voltage protection for "speaker voltages".) Then once you are using op-amps you can add a comparator to light an LED, etc.
...I've made several sound activated (line level) lighting effects using peak detectors and Arduinos. One of those effects is a "Giant VU meter", but it's not calibrated to anything... It continuously self-calibrates to the recent peaks for lots of "meter action" no matter the overall loudness.
I've thought about making an audio power meter with an Arduino but to be really useful it should be auto-ranging, and I have to decide on the number of channels, and I'm probably never going to build it. I can solder-up & assemble the passive peak detector in a couple of hours and there's no programming so I WILL get-around to that someday...