Crate IIR buzz

[BungleFever]

I recently found a Crate IIR with extension speaker for 60 bucks at a music store in boston. It sounded good at the store, everything worked fine. But sometimes when i turn it on now, it has this buzz. The volume on it is turned down all the way, and it still buzzes. Same if nothing is plugged in. I'm not sure what's causing it. Sometimes it's louder than others. the extension speaker doesn't buzz. Not sure if it's a bad connection, or if the electronics are too old, or if something is touching something else. any thoughts?

thanks

[DJPhil]

The first thing I'd look at is the jack for the extension speaker. The contacts in the switching portion might be dirty or may have lost their tension. It might be as simple as that, but if not it's the sort of thing you'd definitely want to rule out.

[BungleFever]

would that cause the main amp to buzz? or just the extension speaker. i've ran stuff through the extension alone and it's fine.

[J M Fahey]

Sorry I don't get it very well.
You say the main amp buzzes and at the same time the extension speker plugged into it does not?
When you are not playing?
Or do both of them buzz at the same time?
That the extension works fine when plugged into another head but buzzes when connected to the main amp?
Or that you play a chord and the sound buzzes through the main speaker but not through the extension?
The 3 possibilities are not the same.

[DJPhil]

would that cause the main amp to buzz? or just the extension speaker. i've ran stuff through the extension alone and it's fine.

If this is what I'm thinking it would (usually) cause everything except the extension speaker to buzz, because plugging something in solves the problem temporarily. I've put a picture in below to help show what I mean. There are several types of switching jack, but this sort let's me demonstrate most easily.

Switching jacks like this are usually used in such a way that when nothing's plugged in the jack is effectively bypassed. When something's plugged in the contacts are under good tension, so everything's ok (right side of picture). With nothing plugged in the contacts have a smaller spot to contact and are under much less force from the natural spring of the metal. If the ground contact was dirty or weak it could cause a buzzing, much like if you hold just the tip of a guitar cord in your fingers while it's plugged into an amp.

When I've faced this problem it was with a headphone jack in a practice amp. Cleaning the contacts didn't help, but if I held the connection closed from above with a toothpick it cleared right up. I wound up replacing the jack figuring it was only going to get weaker over time.

I'm a bit new at all this myself, so this is just a first guess at what might be an easy fix. Mr. Fahey is one of the many professionals here, so working with him should be much more promising.

Hope that helps.