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In my jcm800, I get this strange feedback at certain levels and certain times that I cannot get rid of. Im pretty its not an issue of too much gain, as the 800s are really high gain and the low-mu phase inverter brings the gain down even more. It also comes and goes if I turn the volume and gain controls up, and the only way to rid of it is to turn one of the controls down. Its not a low 60Hz hum, and its not a shrieking feedback due to much gain. Its somewhere right in the middle. I installed a 'high gain' switch by bypassing one of the cathode resistors with a capacitor, and although it still isnt terribly high gain the strange feedback is very prominent when its on.
But as I mentioned, it only occurs most of the time, not all of the time. Sometimes with the high gain switch on the feedback isnt not there, but if I smack a power chord it gradually fades and wont go away unless I turn the switch off.
I dont know where to look to troubleshoot this.
But as I mentioned, it only occurs most of the time, not all of the time. Sometimes with the high gain switch on the feedback isnt not there, but if I smack a power chord it gradually fades and wont go away unless I turn the switch off.
I dont know where to look to troubleshoot this.