KB60 IC questions

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Re: KB60 IC questions

Post by Enzo » Sat Jul 28, 2018 8:35 pm

Offhand, without seeing it...

SO check the reverb control. If the pot is open near one end or has lost a ground...

I talked about the 4-pin molex earlier, right next to it is the two -wire molex to the reverb jack on the panel. Unplug that molex. Any help?

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Re: KB60 IC questions

Post by dak » Sun May 21, 2023 8:25 pm

Just because I hit upon this old thread on a search: my take on it is actual feedback: for some reason the amplified reverb tank output manages to sneak back into the reverb input. Nominally that could happen through R191 and R134, but their connection is on a virtual ground provided by U5B through R130. That virtual ground is a blend of two different grounds that should be connected (the blend is for compensating hum injected via different paths to the blending point). The connection should be essentially zero ohms in order not to help with passing signals via the ground line.

There are a few other possibilities for accidental connections/non-connections that might make the reverb output feed back into its input.

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