Nashville 400 (Round 2) Hot Hummmm

[psmith]

well this thing had a hum to it, would go away if you flipped the ground back and forth, only to come back......i tightened all the pots, they were ALL loose, and that has been fixed BUT BUT BUT

Now it has a worsened version of something else it was doing. This is like an input hot hum thing going on, here's what we have

-when nothing is plugged into the amp, you can put your hand on the corner by the inputs, the cab by the inputs (just the cab <wood/tolex> by the inputs) and it will hummmmm hummmmm till you take your hand away, like touching the hot of an input jack.

-this is not affected by the ground switch

-goes away if i turn either vol pot off

-*****when i plug into either one of the input jacks, it goes away

-I replaced the input jacks with new ones and it seems like it's worse?

Is this an input jack problem? I've never encountered this one before. Did i replace a potentially bad input jack with a worse one or am i missing something here?

Any help would be greatly appreciated!

Patrick Smith
Shreveport, LA

[Enzo]

Yes, it is an input jack problem. There are little contacts on the jack that ground the tip when nothing is plugged in. This is to prevent noises like you describe.

If that contact gets bent, or otherwise fails to make contact inside, then what you have results.

Either replace that input jack, or service the cutout contact on it. And make syre the ground connection is solid. SOme of their jacks have little points on the gront surface to make contact with the panel. If you replace them with similar looking jacks without the little point, you will not have a ground connection there. In these cases I usually lay a piece of thin solid wire next to the jack bushing and solder the end of it to the ground pad underneath. When I mount the board, the little added ground wire is pressed betwen the jack face and the chassis wall to make good contact.

But if the amp works OK when you plug into it, why bother? Leave it turned down when nothing is plugged in. Or turn it off.

[psmith]

Thanks Enzo,

That's kinda what i thought but what i needed to know before i went digging where i shouldn't be digging. I switched these out with reg switchcraft jacks so they likely do not have the little contact thing you described. I saved the old jacks so i can check. But, your point about "if it works fine when plugged in then why bother?" is very well taken. I may do just that Thanks again for the help

PMS

[Enzo]

If you installed jacks without the cutout contact, then it is just the same as the original jack with a bad cutout contact. Weren't the original jacks already Switchcraft? Like the 49 series?

[psmith]

"......then it is just the same as the original jack with a bad cutout contact. Weren't the original jacks already Switchcraft? Like the 49 series?"

Yup, having checked them, they sure were switchcraft. I'll go back in tonight and work the contact