amp buzz....again

[12AX7]

i posted a while ago about this but i wanted to post again because i found something that may give a clue as to whats going on. The amp buzzes even with HB pickups and it sounds like a single coil buzz. As you know, pickups wired reverse, IE: hot to ground and ground wire to hot can cause buzz when you touch a polepiece, and the polepiece can act like a noise antenna. Thats what i just noticed...if i touch the polepieces on my main guitar it buzzes much louder. It's HSS, but the thing is, the humbucker's plate is NOT attached to the hot. But i figured i'd revese the pups anyways and make sure the plate has it's own wire to ground so i can reverse it with not issues like that. So i brought it to work to do this when i have some free time.

But when i checked it out here, i plugged it into 2 amps and neither had the buzz. One a blues jr, the other a fender ss. So it must be in the amp after all. So i'm here to ask, what in the amp could cause the polepieces to act like that? the in jack is isolated from the chassis and has it's own ground to the ground bar that runs along the board and is first in like up stream. I've used this setup on 3 amps now with good results, and this worked till recenty. So if that clue points to something obvious i'm hoping someone will know, as this is driving me nuts. Thanks.

[12AX7]

No, but at this point i think the buzz isn't too bad and that it just multiplies a lot depending on where and how i'm using it. It must be just normal buzz from a cascaded preamp because when i cut the signal after the 1st stage and insert the guitar there is gets very quiet. So i think the input stage is just picking up a lot of buzz and i've replaced everything from trying different guitars, cables, new jack and 1m resistor and grid stopper and even tube and tube socket and the components in the signal path to the 2nd stage.  Grid stopper is right on the socket and shielded cable is used. So yeah, i think it's just normal buzz from a somewhat high gain preamp that would require being excessively anal in shielding and grounding. Thats why I started the other thread on shielded cables.

It recently got worse, but trying it in different places i think that may be due to something in the tenants upstairs...new PC or some digital device etc.

[Willabe]

It must be just normal buzz from a cascaded preamp because when i cut the signal after the 1st stage and insert the guitar there is gets very quiet. So i think the input stage is just picking up a lot of buzz and i've replaced everything

Or it could be the layout/lead dress? You changed all the components, so layout is left.


                  Brad     

[12AX7]

No, lead dress is fine. In fact, you can chopstick every wire till the cows come home and the amp doesn't change in the slightest as far as noise. I've been thru all that ad nausium even to the point of re-routing anything suspect and concluded the lead dress isn't an issue in the least. I guess it's normal, as even my early (JCM and JMP) marshalls buzzed this much as i recall. But i think it should be possible to make it better. It's not so much that it's noisy but that it GETS noisy when used in conjection with other gear or in certain buildings/outlets. In other words, it's sensitive and will become noisy when the place/scenario in which it's used  isn't perfect.

[jojokeo]

Merlin's grounding link is no good so read my posts here...hope this helps?

http://www.el34world.com/Forum/index.php?topic=9482.msg86101#msg86101

[Madison]

12Ax7, somewhere grounding is a miss in your amp.

Jojokeo, that is an great concept with the cap.
Makes sense.
Thanks for sharing that important tip!

[John]

Attached is Merlin's article about grounding, hope this helps too.

[Jennings]

Stop me if I'm being daft...but have you tried your amp in another location?  Could be there's something at your house that's giving out a lot of interference rather than either the amp or guitar being at fault.  Maybe computers, TVs, lighting, home wall socket earthing etc etc.

[Willabe]

Here it is.

http://www.freewebs.com/valvewizard2/Grounding.html

[12AX7]

Yes, i've tried it in different rooms and other locations and it always buzzes some, tho a lot less than at home in the spot i use it. As i said either here or my other thread,  I now believe the buzz is a  normal small amount that is aggravated in certain locations. It is a high gain preamp style amp, and those will always buzz i think unless everything is located and grounded to sheer perfection. I do think it can be improved tho.

Thanks for the grounding articles. I will certainly check those out, tho i have checked every single ground both for where it's grounded and how solid and i believe the grounding scheme is good. But it definately seems like a ground issue.

[hokenpoke]

Is one guitar in particular?  If so, it may be the guitar.

A friend was having the same problem with a home-brewed Tele and when I took a look inside, he had the base-plate of the Bridge PUP going to signal and then had wired the tip of the output to the shield of the coax that ran from the volume pot to the jack.  Signal was buzzy and thin and the buzz got louder when you touched the strings.  Fixing the problems above fixed all.

[12AX7]

Thanks, but no. It happens with any guitar, even the one i have thats the quietest usually.