The current draw increases significantly when a load is attached. I say "significantly" because I now have a 2A current limit on it. When I attach the load it maxes out and the supply voltage drops to ~9vdc. When I had the current limit set to 4.5A, it maxed that out.
The resistance between the relay input and the high side source is .1 - .2 ohms. I have to hold the probes there for a few minutes to get it to steady reading.
Wow! I connected my larger power supply without any current limiting and using the 50Hz input signal and the amp draw first jumped up to ~16A and then fell and stayed around 9 - 10A.
The output signal looks good at the speaker terminals. Looks like that op amp at U13 was the problem. Before, when using my large power supply is when I originally discovered the problem.
I am going to mount it back into the heat sink and see how it does unless there is something else I should check first.
I believe that I can see it when I change the scope to 100 - 200mv/div.
The noise remains constant regardless of position of pots.
I attached a screen shot of the noise at the speaker output.
There is one of the op amps in the pre-amp section that has 15 vdc on pin 7. None of these op amps have board designations that I can see.