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Author Topic: fender amp hum  (Read 2435 times)

bdaudio

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fender amp hum
« on: April 17, 2014, 05:32:01 PM »
I have a Fender  acoustasonic junior amp that has a loud hum out of the speaker output, along with the hum there is dc voltage, checked output modules did not find any issues, checked the filtering caps as well, current draw is about 230 milliamps without a speaker connected with speaker connected it goes up to about 900ma

Enzo

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Re: fender amp hum
« Reply #1 on: April 17, 2014, 07:52:07 PM »
TURN IT OFF, DISCONNECT THE SPEAKER.

Until you eleminate the DC on the output, NO speakers or loads.

There is a separate power amp for each speaker, determine which one has the problem, or both.






what specifically do you mean by "checked the output modules"?  There are discrete output transistors in pairs per channel.  A short likely will be between C and E leads.

johnjet6

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Re: fender amp hum
« Reply #2 on: November 10, 2015, 10:11:28 AM »
Enzo, I have three of these amps and they all have the same issue.  One hums louder than the other two. It sounds like a 60 cycle hum.  Could this be a capacitor, either in the power section or in the output amplifiers?

Enzo

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Re: fender amp hum
« Reply #3 on: November 10, 2015, 05:07:07 PM »
Can't say from here.  Just take it as three repairs.  It may wind up they have something in common, but assuming that will only cloud things.  LOUD hum is usually either DC on the speaker or broken solder on a filter cap.  Start with the loud one - gotta start somewhere.  Determine if there is DC on the speaker.  And I mean volts of it, not some millivolts.

The amp has two power amps, one per speaker.  Are both speakers humming the same?  Or only one?  You have an insert jack and stereo loop jacks.  Is the hum present on the sends? (Listen through another amp)  If you plug into the returns, does the hum stop?

You can look at the power supplies for excess ripple.