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Behringer ep1500 power rail vs muting circuitry
« on: January 09, 2017, 05:13:55 PM »
Hi all. First post on this board, thanks for the read. I am working on what Appears to be poorly rendered schematics with alot of assumptions in the drawings.  Let me get to the request and then explain the discussion of this thread.

A recent power failure has faulted the amplifier. Upon opening I have discovered that the low voltage opamps were not getting anything more then 5-6 volts across both rails.. (should be 30vdc). Now im showing a -15vdc on one side and 0v on what should be 15v..
Not knowing where power is sourced from directly im assuming a bit that i could have a shorting op amp or the circuit is in a muting or protect mode.

Im trying to discuss the problem and diagnose the amplifiers pathway of power. Reading the schematic shows a few things, but i would like to discuss with you all to solve my issue but learn more of this design .


Re: Behringer ep1500 power rail vs muting circuitry
« Reply #1 on: January 09, 2017, 05:56:14 PM »
A common fault for power amps is output devices failing short circuit, perhaps check there first. 

The EP series is reportedly influenced by QSC's RMX series so a schematic of the QSC might help point you in the right general direction.

John Roberts
Tune it, or don't play it...

Re: Behringer ep1500 power rail vs muting circuitry
« Reply #2 on: January 10, 2017, 12:12:51 AM »
Thanks John. I did read that info, and noted the qsc schematics are much better, although 90 percent is identical, a few extra power transistors and minor tweaks they were generally the same.   There was reference to crowbar circuits and dc shorting to dampen the power rails.

But im not sure on the power supply of the 15v rails. Do they get power from the amplifiers or from the half wave side of the bridge rectifier.. since there is a 30volt signal from the bridge tap, I assumed the signal was center tapped and a floating ground was biased to the amplifiers ground plain.