Behringer Eurolive B212D

[drewl]

It's a powered mixer, and the preamp section isn't amplifying correctly.
I pulled the preamp, ran +/- 15v power supply into it, and if I drop the supply down to +/- 10v it works great, as soon as I bump it up to the +/-15v it kills the output of the first op amp.
I replaced it (a 4560) but it still does the same thing.

Anyone have the schem, or just the preamp?

it's only got 4 TL074's and the 4560, but it's gonna be a pain to sketch out as it's all surface mount, so I thought I'd try you guys.

Thanks.

[Enzo]

Kills the output? Just signal disappears? Or does the output pin slam to DC?

IC1 looks like a 4580, but a 4560 ought to work. Pin1 is the output, so what is on pins 2 and 3 at failure. If the whole stage is power level sensitive, I'd be looking at clamping diodes D1,2,3,4. perhaps one has gone leaky, but only at over 10v.


It looks more like a powered speaker than a powered mixer, I ony see the one channel.

[drewl]

Yeah, powered monitor, don't know why I said "mixer".
And yes, above 10v pin 1 output goes to the + rail.
I'll replace those diodes and see if that does the trick.
What are they using the opto for?

[Jazz P Bass]

Here is the schematic.

[Enzo]

The B212A and B212D are different, but the preamp part is pretty similar if not the same.

SInce the op amp slams over to rail, look at the two input pins and see if the rail shows up there. Those diodes are protective, so the amp works without them. You could just remove the four and see if the amp recovers. If so, then install nice new ones.

[drewl]

Correct again Enzo, it was the diodes...and Pbass thanks for the schem, makes it alot easier to deal with.