Fender BXR 60 bass amp buzz (preamp section) - diyAudio
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Old 23rd March 2013, 11:34 AM   #1
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Default Fender BXR 60 bass amp buzz (preamp section)

Got this amp in with a couple of issues. Non working tone controls and buzzing was the main complain.

I managed to fix the tone control problem. Checked the power supply and the main filter caps were not soldered to the board, instead just being held in place with a blob of solder. Repaired that but the buzz still persists.

It has a preamp out and power amp in section. Checked the power amp and it tested fine. Ran the preamp out and it was buzzing. The buzz comes when the volume is raised and the tone controls affect the buzz. Pressing the notch filter button eliminates some of the buzz but its still there.

The input runs into a TL072 IC, thought this was the problem as the buzz got louder if I placed my finger on it. Waved my hand around it and the buzz gets quieter...weird. Changed it out and the buzz is still there but waving my hand around it does nothing now. Checked all electrolytic caps and they're all fine. All other TL072's on the board are fine. Checked the 1/4 inch jack connectors and they tested fine.

Inserting a jack into the input makes the buzz a lot louder as the jack separates the input from ground. Using a guitar pickup works but the buzz is still there. Tapping the board around the input jack section where the first TL072 is causes the buzz to get louder but with a lower tone, sounds kinda like tapping a microphone. Any ideas? At the moment I'm in the middle of testing components around the input section but they check out so far. Gonna check around the notch filter next...
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Old 23rd March 2013, 05:08 PM   #2
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Here's the schematic of the preamp section.

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