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Topic: Fender Squire Champ 15 Solid State Question |
Nick Reed
From:
Russellville, KY USA
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Posted 10 Nov 2013 6:48 pm |
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I have a small Fender solid state practice amp that has a buzzing hum when first turned on. After about 8 to 10 minutes the bad noise goes away and the amp then sounds fine. Anybody know what could be causing this?
I did find this link online at: http://www.somewhereoutwest.com/squire_buzz.html
Do any of you Electronics GURU's think I should try this guys fix? |
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Paul Arntson
From:
Washington, USA
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Posted 22 Nov 2013 1:42 pm
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I think that shielding idea is excellent.
Easy to install, just make sure it really makes contact where you want it to and doesn't short anything else out. A piece of cardboard glued on the inside would probably work fine for an insulator.
If you are willing to be an extreme do it yourselfer, a beer can with the lacquer sanded off the electrical contact surfaces would probably work. You can check it with a continuity tester before you screw it in place.
Hardware stores often have sheet brass that would work, too, and you can solder to that.
His comment about the increased hiss is probably right on the money. I don't imagine this increases it, just doesn't mask it anymore.
Inexpensive transistor amps often have a fair amount of hiss. |
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Michael Maddex
From:
Northern New Mexico, USA
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Posted 22 Nov 2013 7:33 pm
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Nick, this guy writes
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| In a bit of undocumented work, I took a piece of aluminum foil and shaped it to fit around the input section. Nothing too tight, mind- I didn't want to short anything out. I just built a shell around that area. Lo and behole, when that aluminum foil shield made good contact with the chassis, the buzz disappeared. I decided to build a permenant shield and mount it. |
I would try something fast and easy like that. Based on the results of that sort of experiment, I would decide if I wanted to go all out with a fix like he describes. HTH.
_________________
"For every expert, there is an equal and opposite expert." -- Arthur C. Clarke |
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Paul Arntson
From:
Washington, USA
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 24 Nov 2013 5:36 am
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| If the noise goes away after a period of time, it likely has nothing to do with shielding, or the lack of it. I would guess this problem to be a bad filter cap, one whose value is changing (raising) as the amp heats up. The ratings are often pretty sloppy (PORM 20%) on electrolytics, and that much of a shift can significantly affect how well they filter, especially in "brute force" power supplies, those which have no regulation. |
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Paul Arntson
From:
Washington, USA
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Posted 24 Nov 2013 11:47 am
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Donny is right. I was adding my own bias from past experience about noise in unshielded circuits coming and going and I wasn't reading the symptoms as described.
The shielding thing is so easy, I personally would try that first maybe with some tin foil and paper or plastic insulation, and then if that didn't work, move on to replacing a filter cap Like Donny said.
If you're careful not to heat up the circuit board too much when you solder it, it's a fairly easy fix.
It could also be another capacitor breaking down and causing a low frequency oscillation (motor boating) also. A little harder to find.
It could also be a cold solder joint only needing to be redone. (You're right Mike, reflow wasn't the right word.)
Last edited by Paul Arntson on 24 Nov 2013 1:40 pm; edited 1 time in total |
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Mike Wheeler
From:
Delaware, Ohio, USA
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Posted 24 Nov 2013 12:55 pm
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To me, that symptom sounds like a classic cold solder joint at one of the filter caps. If a visual inspection doesn't reveal anything, I'd resolder (not just reflow) all the caps, then test it further. Cold solder joints can sometimes be difficult to see with the naked eye.
Of course, having an oscilloscope would make the job much easier.
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Best regards,
Mike |
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