Start by trying to locate the source of the noise. Turn down all of the controls and turn them up one at a time, making note of which ones if any, makes the noise better or worse.
Try using a high value cap to ground out the audio signal coming from the two preamp boards going in to the power amp. Or you could just unsolder the two blue wires from the pre amps to the power amp input. That would isolate the power amp circuit to see if the noise is being generated there or in the pre amps.
The actual noise can be generated by transistors, resistors and sometimes caps. Finding the actual source is sometimes difficult. Once you have found the general area of the circuit, you can use a capacitor to shunt the audio signal to ground and listen to hear if the noise is shut off. Then you will know that the noise is being generated somewhere in the circuit ahead of where you grounded out the signal.
Some people will just rebuild the entire circuit hoping to cure it. This will work to a point, but requires a lot of parts and a lot of organization to not install the wrong part in the wrong place.
Breakersbass Messages: 13 Registered: August 2015 Location: Summerville,sc
Junior Member
OK great. The noise is there with all of the controls turned down, no signal input, and does not seem to change when I increase any of the controls.
I will go ahead and isolate and let you know what I find.Are any of the transistors Germanium? I understand from the old days that theses dudes are noisy.