February 5, 2013
about 2 years ago
I did some more testing, and I am measuring up to 1V AC on the DC input pins while the amp is “motorboating”. If I turn down the gain, then the voltage goes away as the noise stops.
I tried adding a couple of capacitors (100uF) to the DC input, that didn’t do anything.
There has to be something I’m missing…
I’ve built a couple of these kits and they are great.
I’ve interfaced one with a Kemo M040N universal pre-amplifier. Again, the sound quality is great, nice and loud.
If I turn the volume up more than about 20%, the amp looses control, and just starts rumbling.
If you look at the wiring instructions for the Kemo Preamp here:
It shows the input and output, and DC negative, all tied together. That’s how I have it wired up. However, even with no audio signal, the amp just starts rumbling like crazy.
If I power the Kemo from a separate DC supply, then it works perfectly, up to full volume. Clearly the signal is coming from the power somehow. My intended application is running from a 12V battery, so separate power sources will not be an option.
How do I isolate the DC inputs to each part? I guess I need way better filtering for the power amp.
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