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i have a peavey mark lll bass 400 watt amp head. when i turn it on it makes a very loud hum. if i leave it on more than a few seconds it will blow the fuse. i don't even have the speaker pluged up and, you can still hear it hum. the light in the room goes dim also. can somebody tell me what it might be?
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Stop turning the amp on!
You will only make an already failed amplifier worse.
You may have a blown output section or the power supply is bad. -
change your filter caps first get them from antiques electronics supply, last time I checked peavey was out. They will probably recommend 4700uf 63v caps for the output.
jasonsoldering stuff that's broken, breaking stuff that works, Yeah!Comment
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I wouldn't just start randomly replacing parts based on a previous experience. You need to troubleshoot the amp to find where the problem is. I would start by checking for shorted output devices. If the filter caps are bad, you can check that by floating the power supply.Originally posted by nosaj View PostComment
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Most common cause for loud hum and popped fuses is bad output tubes. But like others recommended, unless you're a tech, I wouldn't keep trying this at home.Comment
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Well, there are no tubes in this solid state amp, but I'd agree there probably are some bad output devices - transistors though.
I vote there is a shorted semiconductor/s. Output transistors likely, main rectifiers second on the list. I doubt the hum is just ripple from weak caps if the room lights dim.Education is what you're left with after you have forgotten what you have learned.Comment
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Well, you know, I threw that just in case he has a tube amp lying around with very loud hum and blowing fuses....Originally posted by Enzo View Post
(Oh dear, that was reckless. I'm seeing tubes. Sorry about that, stompjumper2007, my bad. )Comment
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