amp buzz

[daz]

This amp (homebrew, similar to 2204) has had buzzing a few times in the past which i've found and fixed. Once a bad mid pot ground. But this time i cannot find it for the life of me. It is NOT a hum, but a buzz very much like single coil pickup noise. Happens with any guitar, (have 3) humbuckers or SC. And if i take my hands off the strings or any grounded part of the guitar it's at it's worse and touching a grounded part lessens the noise more and more the harder i touch it.

I came to believe it is in the first stage because if i inject the guitar signal anywhere after the gain pot theres no buzz at all. If i pull any tube, no buzz. i have literally swapped out everything from the input jack to the gain pot INCLUDING the gain pot and even the belton socket for V1. I then started wondering about filter caps and replaced the JJ 20/20/20/40 multicap with no relief. It then it hit me i never replaced the main 100/100 filter, but wouldn't that cause noise in all stage if it has issues? So at this point i am so lost i don't know what else to do. Every solder joint and past in the first stage was replaced up to the V1B grid. All grounds checked and in the 1st stage i hit them all with an iron or sucked up the solder and reflowed them. Tried different cables too. Tried different rooms to try different A/C outlets.

I don't think theres anything left for you to advise me on, but i have no other resources so i figured i'd at least ask rather than just give up and live with it. Thanks.

[Chuck H]

How is your input lead to the first tube grid shielded? If it's a shielded lead, where is it grounded?

Are there any cheap ceramic caps in the first stage circuit?

You mention a multi cap. That means that some filters could be sharing grounds in a less than ideal way.

This might seem insulting, but have you tried a different instrument cable?

[daz]

How is your input lead to the first tube grid shielded? If it's a shielded lead, where is it grounded?

Are there any cheap ceramic caps in the first stage circuit?

You mention a multi cap. That means that some filters could be sharing grounds in a less than ideal way.

This might seem insulting, but have you tried a different instrument cable?

It's shielded and the shield is connected at the jacks ground. But oddly i removed it and used s plain unshielded wire and it actually sounded like it was slightly less noisy.
No ceramic caps anywhere.
The multicap's single ground for all sections is grounded at the main chassis bolt where the main filer and PT is grounded.
Tried several cables and guitars. No change at all.

This is just wacky because i have replaced everything from the input to the 2nd stage grid. I can't see what could cause it because of that, but it's somehow happening between the input to the 2nd stage. I even put a new jack and 1M ground resistor in just now (2nd time i replaced those) and no change. This is just nuts. I thought of something while typing this...i'm going to ground the jack somewhere else. Seems senseless since that hasn't ever changed and the amp wasn't always like this. But i'm wondering if some change i made cause that no longer to be the ideal place to ground the input. So i'll try that. Probably be about the last thing i haven't done.

EDIT: just disconnected the input jack's ground and used a clip lead to try it grounded all over the amp. No change no matter where i grounded it. Did the same with the multicap's ground. I'm afraid i'm going to have to build a whole new amp to get relief from this buzz. I just don't see what else i can check.

[Chuck H]

Have you tried isolating the input and/or output jacks? It seems to help some amps depending on ground scheme.

Some part of your ground scheme is less than ideal. Since you've been using the amp somewhat happily I'll guess that the problem isn't severe. Lots of vintage amps have a less than ideal ground scheme. And they buzz as a result. The multi filter can could be the problem. Ideally the preamp filters should be grounded with the preamp. You might try lifting the first tubes filter connection to the multi cap and use a single cap grounded at the preamp to see if it helps.

FWIW the practice of replacing parts without being able to positively identify them as a potential source of the problem rarely solves the problem. Replacing the input jack twice is a little manic. Once is enough to know if it fixed the amp. The coupling cap wasn't a likely source of this sort of problem. etc. As often as not the random parts replacement method of repair causes more problems than it fixes because you may develop a new problem that confuses the original issue. The problem is most likely ground scheme or layout related. In which case there was never any need to replace any parts. You could have saved yourself a lot of trouble if you had asked first. But I know you don't mind soldering.

[Steve Conner]

Did aliens implant any sort of transmitter in you lately? That could be causing interference.

It sounds like the classic electrostatic hum pickup caused by poor grounding. It gets better when you touch the guitar strings because this brings your body to the same potential as the chassis, and it acts as an electrostatic shield.

I'd be looking for changes in the environment, not the amp. Maybe the ground wiring in your house has gone bad, and your amp isn't grounded any more.

Out of interest, does the buzz go away when you turn your guitar volume knob down to 0?

[Chuck H]

+1
I wanted to go there, but I thought that an improperly grounded preamp could also cause the "touch" symptom. As in, if there is some sort of ground issue Daz's body could actually be grounding the loop. It seems odd that house wiring could go bad without other obvious symptoms around the home. But I will say that many houses here in the US are grounded via a three foot iron spike pounded into the earth with a copper lead screwed to it!?! So I'll back the idea of trying the rig in another environment. Also... Try the rig through another amp with similar gain. I know Daz is REALLY particular (not a bad thing Daz). A little buzz is normal due to the very extreme amplification factor of a guitar amp. It's impossible to eliminate some noise without eliminating some performance. You could do seperate power amp and preamp chassis, isolate your grounds, follow ideals and use Faraday shields and $h!t and the results would probably be dissapointing.

[Steve Conner]

Well, I once had the ground wire come loose from the outlet where I plugged my amps in, and it caused some quite similar symptoms to what Daz described.

I've built high gain amps that don't hum or buzz at all. You can crank all the knobs to 11 and all you hear is hiss. But as soon as you turn the guitar volume up from zero, the buzzing starts, because even humbuckers pick up some hum. And often the guitar wiring picks up some electrostatic noise too.

[olddawg]

Even a neighbor using a triad light dimmer or motor control can cause this. Try connecting your ground to a cold water pipe. Or...see if you have the same problem in a different location. I have one club I play that has a horrendous buzz. I don't have it anywhere else. It's the transformers for the lights for the gas station next door.

[Dave Curtis, dB AudioTech]

"But I will say that many houses here in the US are grounded via a three foot iron spike pounded into the earth with a copper lead screwed to it!?! "

That's the supplemental ground rod; it's eight feet and either copper-clad zinc or galvanized steel, and for about 10 years now, we've been having to drive 2 of them, at least 6 feet apart.
The actual ground comes from the utility, and if that somehow fails (I've seen it), the ground rods will provide the grounding.

Maybe a few use a (non-code) 3' iron rod, but many have a single 8' (listed) ground rod.

[Jazz P Bass]

Yeah, and without the ground rod, your 'ground' is tied to your neighbors.

[daz]

Ideally the preamp filters should be grounded with the preamp

I did try grounding the can there along with a number of other places as i mentioned in my last post. Of course with a multi can the others were now grounded there too, so i will try the suggestion of a single cap for V1 grounded there.

Replacing the input jack twice is a little manic

Well, it would be but i had a reason to do it the second time. It's a isolated jack, but it's metal and isolated via heat shrink on the threads along with a fiber washer. So i feared it might be making contact because it wasn't very secure from touching the chassis, nor was the 1st jack. So to make sure this doesn't happen and compound the issue making it much more confusing i put a jack with plastic body/threads this time.

ut of interest, does the buzz go away when you turn your guitar volume knob down to 0?

yes, 100%. Same if i turn the gain to zero. Same if i remove any tube. So it's gotta be a PSU thing as far as i can tell. Now heres something that could be a clue. I had the multi can under the board mounted outside with a hole for the top like a marshall's cans are mounted. The amp hummed so recently i removed it and mounted the can inside the amp against the end of the amp the PSU is at and the hum disappeared. Fearing the long runs to the various nodes would cause noise, i ran them thru a hole in the chassis (rubber donut, teflon wires, and heat shrunk for safety) near the cap and each wire splits off from the group near it's destination. I figured with those long runs they'd be less likely to create issues being separated/shielded from the rest of the circuit by the chassis. And while i wonder if that could affect it by being near the trannys, i don't recall this buzz right after i did it. Tho maybe i'm mistaken and for some reason didin't notice it due to being thrilled with the loss of the hum it cured. I dunno. Can the wires running near either tranny or the choke cause this? And if it DID cause it, i'd think it would not be due to being near the PT or choke, just the OT. But if that was it, why does it seem to cause buzz only in the input stage? I can connect my guitar to V1B bypassing the first stage and granted the gain is much less, but it's just about dead quiet. So i don't think thats it, but i mention it because you guys may see a flaw there that my non tech mind doesn't.

As to grounding of the house, nothing has changed af far as i know and i've tried it in different rooms with no change. And in other places besides home it buzzes too. And lifting the ground at the A/C makes things much worse. I also have one of those noise filter mains sockets in the amp. But i replaced that with a regular socket and no change so i put the filtered one back in.

[Chuck H]

What kind of strings do you use? I read that some strings use a clear coating that reduces the effectiveness of your guitars ground.

[daz]

What kind of strings do you use? I read that some strings use a clear coating that reduces the effectiveness of your guitars ground.

Thats a good point, i never thought of that. It's not my issue, as i use regular old EB slinkies and the noise goes away equally whether touching them or other grounded parts. I do wonder tho.....I DID change from dadarrios to Ernies sometime around the point this started give or take a few months. Maybe it was always this buzzy but the dadarrios conduct better? They ARE shinier than the ernies.

[daz]

Ah ha ! It IS the house ! At least for the most part. I tried 2 other outlets before, but i tried all of them today and one was much quieter. I'd say 80% reduction in buzz. The amp still buzzes, but i think to a degree most other amps i've owned do. So heres a new question....is there any kind of line filter or such i can get that will reduce it? The mains socket on my amp is one of those filtered ones, but it does nothing. (i know because i tried a non filtered and it made no difference either way) I live in a back house but is physically attached. So the person who lives in the other portion may have done something like adding some lighting or whatever thats causing this. She's rather absent minded and wouldn't put any effort into trying to help, so when i asked her she just said she can't recall what she may had added around that time and that was that.

So if anyone has a suggestion as to a mains filter that would help please post.

[Chuck H]

If the trouble is the AC ground you won't be able to "filter" a proper ground into the line. If the trouble is EMF then filtering the AC mains won't change that. I think there is a "ground fault" tester that can be bought at hadware stores and such. If there is a problem with the house ground you'll want to fix that anyway. If it's EMF you need to track down the source. Light dimmers, flourescent ballasts, etc. I've seen one case where the power to a housing development used a big conditioner of some kind at the pole. Not those big cap ballasts but what I assume to have been a box of silicooties. Nice even 120VAC and a bad buzz on the line that couldn't be filtered out because of what I'll guess to be some kind of high speed switching. I know a guy who lived close to a railroad line. He always knew when a train was coming because he could hear the track switch relay when it was powered on. And I was shocked badly at a bar gig where the outlets had been wired with random polarity and ground connections. Lot's of things to look for.