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I'm interested in buying a used crate rfx120 combo amp at 1/5th the new price but the owner says it has a hum thru speakers when not playing. research on the web has also brought up this problem. Is this inherent to this amp combo? Worth fixing? or more pain than its worth
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Hum problems can be minor or major. However, there is a better than even chance in this case that it is minor.
I don't find any schematics anywhere for the RFX120. It's not on the service portal... may have been designed just before SLM was sold off and didn't get transferred. I do see an RFX65, which is a solid state amp.
Crates are notorious for having problems with the normalling switches in the jacks. The contacts oxidize or corrode and cause problems, especially in the FX loop jacks. This could be a case of a bad jack switch in the input jack.
Use DeOxit D5 on all the jacks and run a plug in and out a few times. If that doesn't solve it, a good visual inspection of the board(s) might reveal a broken solder connection... especially on the jack terminals.
It could also be a power supply filter cap problem.. if the hum is a 120Hz buzz, that's a good possibility. If it's 60Hz and more mellow, then it is more likely a ground problem.
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