Ampeg B2RE limiter light-distorting

[BStringThumper]

Hello,

I'd like to say first, a big thanks to Enzo for all the help he has provided to everyone on this forum. I’ve been reading his posts to other people who have had problems with their amps, amazing. Enzo must be the best tech guy out there.

I'm hoping for help with my problem. I recently acquired an Ampeg B2RE bass head. I was hoping for some advice.

The amp powers up fine, when you hit a string it is working perfectly, then the limiter light comes on and the sound distorts. If I lightly tap on the chassis the limiter lights turns off and the sound is fine again. I can tap on the chassis with no string/signal input and watch the limiter light flash with every tap, it can be heard through the speaker, too. Then it will work fine for a couple minutes and cut out again, with no movement of the chassis. It looks like this amp was dropped hard at one time, the rack mount tab looks like it’s been straightened, so that couldn’t have been good for the solder joints. I started checking grounds. The transformer was loose and flopping around, I snugged that up. I haven’t pulled the boards out yet to look for solder cracks. I thought it would be best to ask a PRO before going that far. I took the cover off and powered up the amp, with a wood dowel I tapped and pushed around on the board. Pushing on the circuit board did not make the limit light come on, but if I tapped on the board, more towards the left front of the main board, the limit light would flash every time. It seems like a microphonic thing, but with no tubes (solid state).

Any thoughts would be greatly appreciated. Thank you.

Brian

[Jazz P Bass]

Ampeb B2RE

Sounds to me like you need to warm up the soldering iron.
Without trying to be officious, I would resolder the whole board.
Take your time. Check your work by holding the board up to a bright work lamp.
(you don't want to have any bridged circuits, by you or the manufacturer)

[BStringThumper]

Ampeg B2RE limiter

Hi Jazz, thank you for the input. I was hoping to determine possible solder cracks by pushing on the boards while powered up. It didn't cause the limiter light to come on. The mechanical vibration from tapping on the boards or chassis will do it every time. I just read that High K capacitors (ceramic EIA Class 2 can be microphonic, so can Film Capacitors. That surprised me. I did read that solder cracks are in issue with these, so I think you're right, just in case, I'll be soldering for a while. Thanks. Brian

[52 Bill]

I'm with JPB here, you probably have a bad solder connection somewhere on the PC board. Don't think microphonic, think loose or broken connection.

Instead of pushing on the board, try pushing or hitting some of the individual components on the board. I always start with the larger things like electrolytic caps and power resistors, as they tend to come loose from their own weight.

And don't forget to check any board connectors, as they often either come loose from the board or lose contact grip.

[BStringThumper]

Ampeg B2RE-limiter

Hi 52 Bill. Thanks. It's hard to get access to some of the components, but the limiter light will flash even when I tap the chassis with my finger. But when I push the board with a wooden dowl, trying to open up a trace or connector, it works fine. It seems to be a mechanical vibration that is amplifying the signal to cause the limiter to kick in. Well, that's my guess for now. Thanks for any thoughts. Brian

[Enzo]

I would resolder the larger things first. It is parts with some heft that are more likely to break free. Vibrations and impacts won;t usually jar a 1/4w resistor loose, but something like a large filter cap sticking out from a board is a prime candidate. First thing I check on all those Fender solid states with the wedge shaped chassis - main filter solder. SO here, check the main filter caps, the large cement power resistors, 5w and 10w.

[BStringThumper]

Ampeg B2Re-limiter

Hi Enzo, Thank you for your input. I did see some large cement resistors looking down the board. Looks like I'll be doing some resoldering. Thanks. Brian

[Enzo]

I see at least four big fat caps as well. I see six jacks. And this is all just the power amp.

[BStringThumper]

Ampeg B2RE

Hi Enzo. Wow, the jacks can cause this type of problem, too? What component in the limiter circuit detects the signal overlimit? Sounds like I need to resolder everything. I hope I don't cause more harm than good. I'm hoping to pull the boards this morning. Thanks. Brian

[BStringThumper]

Ampeg B2RE - FIXED!

The B2RE is fixed. Thank you to everyone for your input. I found two broken solder points. They were really hard to find. It sounds great. Thanks again.

Brian