New express HUM

[bkorthals]

Hello all,

I have recently built an express. It sounds awesome except for the hum i get. The hum is not there without the guitar plugged in. The level of the hum increases with the volume and is not noticable when the amp is at about 2 on volume. However at 12 it is unbearable. But when I start playing it is not really noticable. My 50 watt plexi that I build has the same issue. I took the amp over to another house to see if that helped but it did not. The hum is the same if I use humbuckers or single coils with the bpssc. Any suggestions?

[DHHZ]

Are you sure that it isn't the guitar? If it's the same problem with all of your amps, and there's no hum without the guitar plugged in, then that's what I would suspect. See if you can borrow another guitar to try. Alternatively, try a new (shorter) cable. It could be picking up radio interference.
Good Luck,
Daniel

[bkorthals]

I played my guitar through a JCM 800 at a buddies house and to me it produced an accetable level of hum... Although I only had the master at about 9 o'clock. Maybe it's just cuz I crank the shit out of my amps and don't use a mv. Should the express be quiet at 1 o'clock ?

[billyz]

Do you have the entire chassis shielded when in a cabinet? I.E. with a metal cover, screen, aluminum flashing stapled to the cabinet covering the open side of the chassis and grounded?

[paulster]

About 1-2 o'clock on a gain control is always going to be one of the levels most prone to noise.

On a log pot it'll be about halfway in resistance terms between both ends of the track, so it'll be around 500K on a 1M pot. This means you have the highest possible source impedance and it's therefore more prone to noise at this point.

Not that this will help you diagnose the problems with your Express but when you're trying your guitar on another amp you want to have the master dimed and the gain at about 1 o'clock as well to give you a fair comparison.

The Express is really finicky about guitar wiring/shielding. My Les Paul R9 had been no problem with other amps but was awful for noise with the Express and Liverpool. I eventually used copper shielding in the pot and switch cavities to make it usable. My 335, on the other hand, is fine and I've got no way of getting in to shield that.

[bkorthals]

I do have a bottom plate for the amp. I assumed it was grounded by touching the chassis. It does not make a difference in the noise.

[Structo]

Does the hum change in relation in your proximity to the amp?

With my single coil guitars I get hum, even on the shielded ones.

If I turn my body slightly to a different angle I can all but eliminate it.
And if I move away from the amp the same thing.

[bkorthals]

The hum does not really change as far as distance... But if I move the guitar from side to side it does reduce the amount of hum... If I sit just right it does become bearable.

[ClassicRocker]

The hum does not really change as far as distance... But if I move the guitar from side to side it does reduce the amount of hum... If I sit just right it does become bearable.

I'd try another guitar ... if the single poll pickup cavity is not shielded properly, this will create the same symptoms. I have this with ANY amp and one of my Strats. If your guitar is a Stratocaster, that's your issue. Try a Les Paul or a PRS. It's AC noise. Do you have this issue in different rooms, buildings, pubs?

This may sound silly, but turn off any CRTs or screens that may be nearby, and space heaters too.

Edit: I just read your first post and see you tried different guitars. Isn't it interesting that you take it to a different environment and it goes away. Try turning off the TVs and space heaters -- when this happens in my band's practice studio, it's usually one or the other.