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Author Topic: Amp help!!  (Read 2997 times)

Mike Steines

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Amp help!!
« on: May 12, 2012, 10:38:20 pm »

Hey guys, I need some help with an issue with an amplifier.  I have a Mackie fr2500 and Im running 2 harbringer hx151 cabs off of it.  I have it set to Mono 1 signal input and 1 cab on each channel.  For some weird reason channel 2 will fade away and cut out at lower volumes then pop back on when I crank it.  I have switched cabs and speaker cables and even ran in stereo to try it and it still did it on channel 2. as long as the music is loud it doesnt cut out.  Any ideas? Im pretty good with repairing electronics but I dont know where to start.  All the mosfets read good so im not sure what else to look at. Any ideas???  I have a buddy that has a peavey amp and its doing the same thing as well (his own system) and im hoping to be able to fix them both!!
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Ivan Beaver

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Re: Amp help!!
« Reply #1 on: May 12, 2012, 10:50:44 pm »

Hey guys, I need some help with an issue with an amplifier.  I have a Mackie fr2500 and Im running 2 harbringer hx151 cabs off of it.  I have it set to Mono 1 signal input and 1 cab on each channel.  For some weird reason channel 2 will fade away and cut out at lower volumes then pop back on when I crank it.  I have switched cabs and speaker cables and even ran in stereo to try it and it still did it on channel 2. as long as the music is loud it doesnt cut out.  Any ideas? Im pretty good with repairing electronics but I dont know where to start.  All the mosfets read good so im not sure what else to look at. Any ideas???  I have a buddy that has a peavey amp and its doing the same thing as well (his own system) and im hoping to be able to fix them both!!
I would suspect either a cracked or dirty connection or a bad connection  in a multipin cable.

Since the problem is intermittant-static measurements of parts will not always show a problem.

This is a common with some of the older Mackie amplifiers.  As far as I know swapping out the ribbon cables fixed the problem.  Maybe start there.
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John Roberts {JR}

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Re: Amp help!!
« Reply #2 on: May 13, 2012, 11:59:44 am »

The symptom you describe sounds like a dry mechanical connection (like a jack, or switch, or) that has developed an insulating oxide layer. When the signal voltage is large enough it punches through the oxide layer and conducts, until the layer regrows.

Do you use the same cable with both amps?

It could also be a failing solder connection, again intermittently working after the signal is large enough to make a conductive path, until it stops again.

 Exercise/clean switches, jacks, switching jacks.. etc. Wiggle wires.

Could be a faulty ribbon cable if used (that also makes a mechanical connection). While I am not familiar with lots of ribbon cables inside Peavey power amps, I suspect there could be one.

JR

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Geoff Doane

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Re: Amp help!!
« Reply #3 on: May 24, 2012, 12:27:27 pm »


Could be a faulty ribbon cable if used (that also makes a mechanical connection). While I am not familiar with lots of ribbon cables inside Peavey power amps, I suspect there could be one.


Peaveys may not have had ribbon cables, but the older ones at least, had Molex connectors, which have become notorious in the audio world for creating just the symptoms you describe.

Exercise (un-plug and then re-plug), and possibly some DeOxit, would be the usual fix.

GTD
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John Roberts {JR}

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Re: Amp help!!
« Reply #4 on: May 24, 2012, 12:41:15 pm »

Any mechanical connection is susceptible to oxidation and/or contamination with the voltage punch through symptom (including, connectors, switches, jacks, etc).

Peavey used and probably still does use lots of ribbon cables. I recall seeing plenty in top head power modules, not so many inside power amps, but I have been outside the walls for a long time.

JR
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Re: Amp help!!
« Reply #4 on: May 24, 2012, 12:41:15 pm »


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