I would appreciate some help with a problem I have. My 1992 Ultimate Chorus has a hum when I turn the amp on, the hum seems to be the same pitch as the note of G when I play the 3rd fret on the 6th string, it gets louder and more bassier when I turn the chorus switch on. When I plug the guitar in and play, the hum level does not alter and the volume control works ok on both channels, however when I play notes on the 5th nd 6th string the sound through the speakers starts to break up.

I have checked out the grounding and that appears to be ok and I have read that the problem may be the solder to the main filter caps but I do not know where, or what, they are. The two jack sockets for the FX send and return appear to be "looser" inside the plastic housing than the other jack sockets but seem to soldered ok to the pcb.

I am not a technician but I have the circuit diagram from Fender and do have a basic understanding of circuits and soldering.

I would appreciate any help and advise anyone can give.

Mike Boland

I'm not incredibly knowledgeable about amps, but it could also be a ground problem with your home wiring as well. You could try plugging the amp into a surge protector, I've noticed that my amps have a little less noise when plugged into the surge protector.
If neither one of those makes a difference and it is something with the amp, if your patient someone a little more in the know will most likely be able to help you out. Good Luck.

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Many thanks Tim, that's something I'll try.

Mike

Check your speakers, chassis and back panel are all tight. I had a speaker come loose on a old amp. It drove me crazy, buzzing like a beehive, worse on bass notes.
When things become loose, they can rattle to certain frequencies.

Other than that, check the speaker isn't worn out. I assume the amp is a twin speaker model with stereo chorus? If so can you disconnect one speaker and run the other. Then swap em over? If it happens on one, but not the other. You've likely found the culprit.

It's a transistor amp, so you don't have to worry about impedance mismatches as long as you aren't going to play for hours using a speaker set up below the minimum speaker ohm setting. Most solid state amps are good for a minimum of 4 or 2 ohms. Most speakers are 4,8 or 16 ohms. So you should be ok for a short test period.

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At last !!! The problem with the hum/buzz on my amp was that one of the electrolytic capacitors on the Mains input to the pcb had a bad soldered joint which I easily fixed.

Thank you to everyone who looked, thought about and replied to my problem.

Mike Boland

Good stuff Mike...Always glad to hear when the solution is easily fixed; without you losing too much time rockin'.

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Well done Mike.

Wonder why positional play bought it to the fore? You got any clues?
Certain frequencies rattling the bad solder joint maybe?

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Don't have much of a clue to the reason why the soldered joint went down - I don't know the full history of the amp but I hope the solution will help others with a similar problem.

Mike

Long live Rock'n'Roll