Orange Crush 20B sounds fine but distorts only on one particular note..?

[cgoodson]

I recently picked up one of these to play around with my el-cheap o bass. I like it okay for what it is, I'm really more of a guitar player. The other day I happened to play a G# on the G strings (first fret) and it sounded like distorted crap whereas every other note I play sounds fine.

So I then played the same note on the D string, it did the same thing. My first thought was that it was causing something to vibrate sympathetically at that frequency so I moved the amp and it didn't help.

Then I considered maybe it was the bass so I plugged in my guitar and played the same note on it, sounded just as crappy as the bass did.

I've checked the amp over inside and out and nothing seems to be loose. Could a bad capacitor possibly cause this?

One thing I noticed when I had the speaker out is the cabinet (closed type) doesn't have anything in there to kill standing waves. Would it be a bad idea to put a piece of insulation in it?

[cgoodson]

I figured it out finally. Although the screws were snug on the speaker if I press on one side of it the noise goes away. So it was simply the speaker vibrating, I would think this would normally happen with more than just one note. Maybe if I put a little bit of silicon around the back edges that will do the trick.

[Tom Phillips]

You

I figured it out finally. Although the screws were snug on the speaker if I press on one side of it the noise goes away. So it was simply the speaker vibrating, I would think this would normally happen with more than just one note...

That one note was at the resonant frequency of the loose parts. It's not an unusual occurance.

Maybe if I put a little bit of silicon around the back edges that will do the trick.

I'm not sure where you mean to put the silicon but I'd recommend against that. If you properly snug up the hardware and none of the nuts/bilts/screws are missing or stripped you should be good to go. Best to solve the core problem rather than adding a band-aid fix.

Cheers,
Tom

[cgoodson]

Actually I tried the silicon trick before I saw your post Tom and it didn't work. Now the noise has moved up a fret to A. I think theres a strong possibility that I was wrong about what the problem was. It seems clear that it is due to a resonant frequency but exactly where it is I haven't been able to pin down. Guess I need to keep poking around with it, any suggestions would definitely be welcome.

[Enzo]

If you can push or press on various places in the amp and get it to stop when you do, then you are on the way to finding it. SO many things to vibrate, so little time on this earth. Push on the speaker magnet, push on the baffle board, push on the top and sides of the cab. Push on the grille, hell remove the grille. Press on the handle. Pull the chassis out and set it nearby, then run a speaker cord or other wiring back to the cab. Does it still buzz with the chassis rmoved?

Cabinet can buzz, baffle board can buzz, speaker can buzz, chassis can buzz. Chassis can buzz itself, or against the cab or against the grille.

The cab can have a joint in the wood that is just barely gapped and resonates. An odd one happens in plywood, sometimes the glue between plies has a void and two interior layers then can buzz, and that is totally out of sight, the actual piece if wood is bad. A screw driven through that spot can cure it though.

HArdware can buzz.

SOmetimes what you presss on is what is involved, but sometimes when you push on the speaker, you are also putting a bit of flex into the cabinet wall, and that stops something elsewhere from buzzing.

In the shop I just plug in an audio generator and sweep it until I hit the sensitive note, then I have have it steadily buzzing with both my hands free.

If you are not sure wher the buzz is, roll up a magazine and hold it to your ear. Then aim it around the amp, it will act like a stethoscope to help pinpoint the source of teh sound.