Bad Buzz From Champion 600

Lands Leaving

Can anyone help me with this,

Basically I installed new tubes and speaker and now the thing buzzes really badly. If I put my fingers on my guitar strings they sort of fizz/pop for a second then the hum goes till I let go. The same fizz sound happens if I touch any of the metal parts of the amp - input jack, on/off switch, etc.

I've tried putting back the stock parts and using a different speaker altogether with no luck, I've also made sure all the screws are tight. It's definitely not the speaker or it's cable anyway, or a tube, but I haven't a clue what else it could be.

Is there a simple solution to this, I can't really afford to send it off to be reapired. (I was half thinking of selling it but until I fix this I can't either do that or use it myself!)

Forgot to add, it's not the guitar (I've tried 4 and they all produce the same result, but no problems in a different amp) or the instrument cable.


Cheers

Eoin Madsen

The amp should definitely not hum in response to touching the chassis - that sounds like a symptom of a serious grounding problem somewhere in the wiring. Open up the plug and check if the ground wire is still connected. But failing something that obvious, it would have to be a broken internal wire, which you won't be able to repair yourself on short notice. If it does have a ground problem, the amp may be unsafe so I would strongly suggest not powering it up again until you've taken it for repair.

Paolo_M

I'd agree with Eoin, it sounds very much like a grounding issue to me.
As you are grounded (by litteraly being on the ground) you provide a pseudo ground for the chassis when you touch it, but you'll also get a bit of coughing and spluttering as you're not a very good ground in electrical terms!!

If you have, and can use, a multi meter then you can check your grounds and repair accordingly. You'd need to start by checking continuity from the earth prong on the plug itself to the chassis of the amplifier (when it's plugged out obviously) and continue from there.
If not then your amp is probably in a dangerous condition and you should take it to an amp tech.

Lands Leaving

Amp tech it is then.

I'd love to know what happened, I only changed the speaker. That isn't even part of the amp itself.

Any idea how much it's gonna cost me?

Eoin Madsen

It could have been a weak solder joint just waiting for a bit of a knock to break it loose. Did you try the amp in a different room?

The jacks, pots, switch etc. are usually grounded by direct contact with the chassis. For the whole chassis to be lifted from ground, the break would likely be in the power cord earth wire or at either end of it. If ground inside the amp is broken, it'd be a quick and simple fix for a tech - but I couldn't guess at how much they might try and charge for it.

Lands Leaving

If it's an easy enough fix for a tech, would it be worth trying myself? Or would I potentially blow myself into next week?

Paolo_M

Lands Leaving wrote: »

If it's an easy enough fix for a tech, would it be worth trying myself? Or would I potentially blow myself into next week?

It would be worth it if you have some basic test and repair equipment (multi meter, soldering iron, spare grounding lugs, wire, strips/snips, etc.etc.), knew how to use this equipment pretty well and knew what you what you were doing electrically, preferably with some form of electrical training.
Otherwise I'd advise bringing it to a tech.

Eoin Madsen

Lands Leaving wrote: »

If it's an easy enough fix for a tech, would it be worth trying myself? Or would I potentially blow myself into next week?

I'm with Paolo on this. Not unless you do a hell of a lot of reading and preparation first. And if by next week you mean dead - potentially, yes. If the ground is lifted, the capacitors in the power supply won't be discharging so there's probably a good 300v or so waiting for you on the B+ line. There mightn't be enough current to stop your heart, but it could definitely **** you right up.

Lands Leaving

Right, cheers for the advice! Just rang xmusic and was quoted 50-100 beans for this... not good value really for such a small cheap amp, but I guess everywhere will have similar pricing.

It's probably not obvious but just in case I'm missing something simple, here's a few pics of the amp's guts in case anyone can see something I can't: