amp buzz

[daz]

Daz et al,
Back in post #11 you verified that the buzz completely goes away when you turn the Guitar volume control down to zero. To me that means that the interference is being picked up by the guitar pickups / wiring harness and not through the mains wiring. Therefore, you need to find what has changed that is radiating the signal that is being picked up by the guitar and the work you are doing related to the AC line wiring is barking up the wrong tree.
HTH,
Tom

I have 4 guitars that all do it and they all either have 1 humbucker or a combo position that cancels hum. They all do it, none have changed, and they didn't do it before. Turning down the guitar grounds the input of the amp, so regardless of what it is that should quiet it. Plus as i said it doesn't do it on at least one outlet in the house.

[Chuck H]

Here's the thing... At this point I'm inclined to think that the problem going away on a different outlet may not be directly related. But rather, that particular area of the house doen't have as much noise that the pickups can hear. The absolute fact is that if you can turn your guitar down to zero and the buzz stops then the buzz is coming from the guitar. Not the AC line, it's not a poor ground, not the amp. Have you tried a new instrument cable?

[Jazz P Bass]

The fact that ' amp turned down & no noise ' does not eliminate triac light dimmers injecting crap directly into the line.

[daz]

Yes, i tried another cable. I'll try a third just to be sure. But i can't imagine a 2 month old belden 8410 i made with switcthcraft ends would be noisy. The other cables i have are much cheesier. I will tho

EDIT: Nope, not a cable issue.

[Chuck H]

The fact that ' amp turned down & no noise ' does not eliminate triac light dimmers injecting crap directly into the line.

Which line? The AC line? I wouldn't think turning the guitar down could silence that.?. If it's the signal chain via the guitar electronics, then of course light dimmers are going to emmit EMF.

BTW, I just tested my house wiring with my meter and got zero ohms between the AC wall plug center pin and the cold water piping. Not that your post above said it COULDN'T be that way. But I think it implied that it doesn't need to be that way.

[daz]

Guys, i think maybe i need to elaborate a bit before you go barking up the wrong tree. If i insert the guitar at the second stage it's dead quiet. Granted, theres one less gain stage to amplify any noise, but from this to dead quiet seems to indicate theres something going on at the input. And also if i touch places with AC signal i get a loud hum just like you'd expect touching say the tip of the jack. But after the 1st stage i can touch any part of the signal path and it makes zero noise. The input is very sensitive. Even as my finger is just right up on a part but not quite touching it you hear hum starting. If i grab the body, not the leads but just the body of the 1M ground resistor at the input it gets loud.

heres another things thats odd and maybe will be a hint. I used to use those russian mullard reissue 12ax7's and they worked fine. At some point after some tweaking i'm sure, they no longer worked right. It sounded like a bad ground resistor at the grid when i'd try them. The note would die and static...you know the scenario. All other tubes i've tried work fine but those. I'm thinking the issue is related.

[Chuck H]

The input is very sensitive. Even as my finger is just right up on a part but not quite touching it you hear hum starting. If i grab the body, not the leads but just the body of the 1M ground resistor at the input it gets loud.

That's normal IMHE

heres another things thats odd and maybe will be a hint. I used to use those russian mullard reissue 12ax7's and they worked fine. At some point after some tweaking i'm sure, they no longer worked right. It sounded like a bad ground resistor at the grid when i'd try them. The note would die and static...you know the scenario. All other tubes i've tried work fine but those. I'm thinking the issue is related.

I hate to say it... I've had a lot of trouble with the rusky tubes. Noisy out of the box or funny intermodulations. NOS tubes are a crapshoot half the time anymore. I'm actually considering Chinese preamp tubes!?! I've used up my stock of RCA's and there's only one Russian tube that sounds "right" IMHO. The Sovtek 12ax7LPS. And those sound great but they're all way too microphonic for the first preamp slot. So I may try the Shuguang 12ax7 for V1.

I know you've checked your input circuit carefully and even tried isolating the jacks. Maybe try your rig side by side with another amp set to similar gain in place of yours. Then at least you can rest knowing the problem is not your gear. I'm still thinking EMF. That's all that's left when you burn it down.

[daz]

That's normal IMHE



I hate to say it... I've had a lot of trouble with the rusky tubes. Noisy out of the box or funny intermodulations. NOS tubes are a crapshoot half the time anymore. I'm actually considering Chinese preamp tubes!?! I've used up my stock of RCA's and there's only one Russian tube that sounds "right" IMHO. The Sovtek 12ax7LPS. And those sound great but they're all way too microphonic for the first preamp slot. So I may try the Shuguang 12ax7 for V1.

I know you've checked your input circuit carefully and even tried isolating the jacks. Maybe try your rig side by side with another amp set to similar gain in place of yours. Then at least you can rest knowing the problem is not your gear. I'm still thinking EMF. That's all that's left when you burn it down.

The tubes are fine. I know because i have 2 of them and last time i used them they worked fine. Now neither work right. Plus, i believe i tried them in the PI and they were fine there.
My only other amp is another build that i sorta cannibalized the preamp on so it's just a PA that i use with a insert point at the PI for a effects return amp. But in any case it's far less noise at that certain mains socket to i gotta think theres something in that room. I patched a few cords together last nite so i could leave the amp there and walk into the room with the "good" outlet and i couldn't get that far. But i got close enough that i don't think theres EMF causing it or it should have gotten quiet when i went in there