Ampeg B4R toubleshooting help, please

Bullitt5135 · #1 11-21-2011, 08:08 AM

Last week I picked up an Ampeg B4R off CL for only $250. I wasn’t able to test it before purchasing, but I was OK with taking the risk at that price. After testing it at home, it seems like Channel A is working OK, but Channel B is weak and heavily distorted (the same sound I get when cranking my VT Bass pedal’s “drive” knob up to 11). I get the same heavily distorted sound when I run it in biamp-mono. Also, I’m hearing a static/crackling sound (through the amp/speaker) when the cooling fan kicks on and off.

Any thoughts as to what needs to be fixed?

Baird6869 · #2 11-21-2011, 08:21 AM

I would take it to an amp tech as the B2R is not exactly a user servicable unit.

I had issues with my B2RE a few years back and it required a few repairs that I could not have done.

Sorry about not being much help, but if you open up the chassis you will see what I mean!

stiles72 · #3 11-21-2011, 09:41 AM

It's possible that the MOSFETS could need the bias adjusted. It's a fairly common piece of mainatanance that occurs with the 3-Pros, and what you describe sounds like what mine did. Take it to a tech, and if it is just a bias adjustment - it should be just a bench fee.

Bullitt5135 · #4 11-21-2011, 09:53 AM

Thanks for the suggestions... the B4R will go to my tech when I pick up my GK. I have a feeling the Ampeg will become my #1 head once it's working properly. Even with one channel out of whack, this thing is pretty awesome.

Bullitt5135 · #5 11-28-2011, 09:34 PM

Strange... my tech called to say he can't find anything wrong with the Ampeg head. He gave the components a thorough bench check, and it sounded fine through two different cabs in his shop. No distortion. I'm going to bring him my Avatar B212 (4 ohm) cab to see if they aren't jiving for some reason. The Avatar is working fine with my GK 700RB-II.

I'm not sure if he checked the MOFSET bias like Stiles72 suggested, but I'll ask.