Fender FM 212 popping sound when switching off

nilhegar · 9th January 2012, 05:45 PM

Hello,

I have a 5-6 year old Fender FM 212R solid state guitar amp which had some problems recently. After a gigging, it started to make crackling noises even if every volume pots were turned down, it did it with every cable, with or without any guitars. Also, it made a loud popping sound when switching off the amp, regardless of the volume settings, it made that sound even if the amp is muted (no jacks plugged in). The crackling noises could be summoned by hitting the top of the amp, so I thought that there are some broke solders inside. So I disassembled the amp, and fixed these issues. Voila, the crackling noises gone, but the loud pop when switching off it remained..

Does anybody have some clue what could be the problem?

Thanks in advance!

Tom

Enzo · 9th January 2012, 11:39 PM

This isn't the first amp to pop when you turn it off, nor will it be the last. Power-off pops are extremely common, and I don;t consider them problems or defects.

nilhegar · 10th January 2012, 08:07 AM

Thanks for the reply!

I have another 212 combo and two fm100h heads with 412 cabinets, and none of them makes this popping sound. I want to repair it, because we run a rehearsal room and a bad amp makes bad reputation for us. Does anybody have any idea how to repair it?
Thanks!

Enzo · 10th January 2012, 08:48 AM

OK then. Leave the power switch ON, but unplug the amp from the wall. Does it still pop that way? Electrically the two methods - switch of pull cord - are the same.

If that still pops, then your pop is likely a turn-off thump. That can be a million things.

If that does not pop, then your power switch is sparking and the amp circuit picks that up as power dies away. A cap across the switch might help, or even just a different switch. Should be easy enough to wire in a different switch to see if that changes things.

Does the amp behave properly otherwise?

9th January 2012, 05:45 PM	#1
nilhegar diyAudio Member Join Date: Jan 2012	Fender FM 212 popping sound when switching off Hello, I have a 5-6 year old Fender FM 212R solid state guitar amp which had some problems recently. After a gigging, it started to make crackling noises even if every volume pots were turned down, it did it with every cable, with or without any guitars. Also, it made a loud popping sound when switching off the amp, regardless of the volume settings, it made that sound even if the amp is muted (no jacks plugged in). The crackling noises could be summoned by hitting the top of the amp, so I thought that there are some broke solders inside. So I disassembled the amp, and fixed these issues. Voila, the crackling noises gone, but the loud pop when switching off it remained.. Does anybody have some clue what could be the problem? Thanks in advance! Tom

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9th January 2012, 11:39 PM	#2
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	This isn't the first amp to pop when you turn it off, nor will it be the last. Power-off pops are extremely common, and I don;t consider them problems or defects.

10th January 2012, 08:07 AM	#3
nilhegar diyAudio Member Join Date: Jan 2012	Thanks for the reply! I have another 212 combo and two fm100h heads with 412 cabinets, and none of them makes this popping sound. I want to repair it, because we run a rehearsal room and a bad amp makes bad reputation for us. Does anybody have any idea how to repair it? Thanks!

10th January 2012, 08:48 AM	#4
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	OK then. Leave the power switch ON, but unplug the amp from the wall. Does it still pop that way? Electrically the two methods - switch of pull cord - are the same. If that still pops, then your pop is likely a turn-off thump. That can be a million things. If that does not pop, then your power switch is sparking and the amp circuit picks that up as power dies away. A cap across the switch might help, or even just a different switch. Should be easy enough to wire in a different switch to see if that changes things. Does the amp behave properly otherwise?

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