Another Ampeg BA115HP Issue...

[n.s.maynard]

I recently acquired an Ampeg BA115HP that looks almost new, but sounds pretty anemic. The Gain and Master need to be at 50% to get anything at all out of it. The CD input works just fine and is very loud.
I picked this amp up pretty cheap and would like to get it working right.
Any help would be appreciated.

[Enzo]

Does the mute switch work?

DO all the controls function as they should, aside from the fact it is too quiet?

I would look down the row of controls and jacks on the front and resolder all. And my main suspects after that would be one of the op amps in the preamp.

[n.s.maynard]

The mute works fine and the EQ controls seem to work as well. I do notice that the volume goes up substantially when the EQ controls are tuned up without touching any volume controls.

I would like to take the cover off of the electronics, but i cant seem to figure out how to get it loose. I have removed the 3 screws on each side but it wont move. Can you tell me what other hardware is holding it in?

Thanks!

[Enzo]

I would expect a few screws down through the top of the cab hold it in place. A lot of times they are wedged in there pretty tight, so even without screws, it can be a bitch to push out.

[n.s.maynard]

Thanks. Once i get it open, what should i look for? How do i check the op amps?

[Enzo]

First thing I do is look for any unwanted DC offset on their output pins. I apply a test signal of some sort to the amp input and trace it through the amp on my scope. I look for some spot where teh signal drops substantially.

[n.s.maynard]

Thanks Enzo. Unfortunately my abilities and equipment are limited to a multi-meter and some basic electronics. Can i check anything with a multi-meter? I did get the damn thing out of the enclosure but have yet to tear into it. I cant see any solder connections yet because of the single sided PCB.

[Enzo]

I use the DC voltmeter to look for unwanted DC voltages on the output pins of op amp ICs.

If you apply a reasonably steady music to the input of the amp, you can use the AC volts to measure signal level here and there.