#1
Alright, so you might have seen my peavey jsx high or he'd squeal thread, which I discovered want the tubes but was the guitar.

But now I have a new issue and I know do a fact it's the amp. Basically I noticed a faint buzzing (which is not helped by the noise gate). I've had the guitar unplugged and the effects loop set to 0 and its still present equally on all channels, even clean. It seems to be directly related to the master volume and presence knob.

I dug into this pretty deeply and found it could be a variety of things ranging from a socket being too dirty, to the circuit board having some serious issues with it. Taking it in to get it repaired or even to find out what's wrong with it is probably going to cost a lot of money, and I've read some cases where it has been taken to several places without the issue being fixed.

If it was preamp tube problem I read it'd be the tube closest to the power tubes which Ive switched out with a new tube (I haven't tested all the tubes though because I don't have any power tubes or much money to buy them with, and I couldn't reach the inner tubes without taking the feet off and taking the whole amp out)

Do you guys have any theory's on what it might be? If not I might return it and either get another one, or get another amp. Although if I got another amp I'd want something similar to the jsx head. So ug, what do you think?
Last edited by zomgguitarz1234 at Feb 1, 2012,
#2
if its what im thinking of, i have the same thing and i have no idea what it is caused by except for a hunch that it may be the power source. i have tested two different guitars and two differents amps (all brand new) and the only consistency with the buzzing seems to be my house. although it doesnt happen all the time, thats still my theory.
#3
Yeah, I hear the power source can be a issue. I might move it to another room or test it at a friends house to see if that's the issue. I might take it for a diagnoses, but I really don't want to shell out 50 bucks and end up havin to return it anyways.
#4
Never touch the insides of an amp chassis unless you are trained - you can die.


Typically, issues like this are tube related. You really have not done any due diligence with your tubes yet so that is where I would start. Get some new preamp tubes and/or at least swap the tube you've replaced already (the Phase Inverter) into the other preamp slots (V1, V2, V3, etc). That is called tube rolling.

For power tubes, for now, I would swap the two inner and the two outer power tubes. Spray the tube pins with some contact cleaner and work the tube in and out of the socket as if they were having sex.

If you need to take the chassis out then heed my first warning please and don't touch anything on the inside. The outside, including the tubes, you can touch all you want - just don't burn yourself.

Report back.

After this if it is still doing it I would get new power tubes if you can afford it. If you still have problems then I would consider taking it to a tech. Maybe there is a bad solder joint or connection somewhere on the circuit board.

Basic amp maintenance my friend. It is really not that hard you just have to do it a few times.

These links I made might help a bit.

http://s545.photobucket.com/albums/hh384/buckethead_311/Amp%20stuff/?action=view&current=Microphonicpreamptube.mp4

http://profile.ultimate-guitar.com/311ZOSOVHJH/blog/80083/


PS: I'm not an amp tech
#5
I'd check for a bad power source or a microphonic tube. If you crank the master, will it squeal? If so then a tube has gone microphonic and needs replacing.
#6
Did the microphonic tube test to all the tubes at max master volume, the only thing that really did happen is the humming went down a bit when I tapped one of the tubes (wut), but I don't know if it's the tube itself because I switched it in and out. I think guitar center gives a free diagnoses though so I might take it there.
#7
I wouldn't take anything to Guitar Center for repair - especially not an amp. They are just going to go 'Yep, there's a problem' and then ship your JSX off to their authorized repair place and charge you an arm and leg when it comes back 3 weeks later.
#8
I recorded a demo of the jsx to show the buzzing, which now appears to be solely effected by the presence and resonance seeing as I had the master volume 0 at one point and the guitar unplugged, and tweaking the presence significantly impacted the buzz

This was done on a pretty cheap mic though, but the buzz is pretty much that bad:
Settings
Clean channel
Presence: Maxed (to show how bad it gets)
Resonance: 12 o'clock
EQ: All 12 o'clock
Channel volume: 12 o'clock
I think the master volume was like barely below 1.

The guitars tone pot was on the deeper end for some reason I didn't realize until after I recorded this

Buzz demo: http://profile.ultimate-guitar.com/zomgguitarz1234/music/all/play1083672

edit: also when the song was over you can hear me turning the volume pot down to 0, and that moment of silence is just the amp buzz which I guess would show it's not the guitar. That's what it's like when the guitars unplugged.
#10
Sounds like a dirty tube socket. Pull all the preamp tubes out and fire the amp up (you won't hurt anything).
If the buzz is still there, put them back in one at a time, starting with the ones closest to the power tubes. You ought to be able to determine which tube or socket is bad.
#11
Just a shot in the dark here but have you tried moving your amp to a different outlet or isolating just the amp plugged into 1 wall socket? Sometimes pedal power supplies or well, anything really can cause alot of noise in an amp that your noise gate wouldnt eliminate. My guess is the fellow's above are right in that its something to due with a dirty tube socket or something but definately if you havent tried a different outlet or isolating it, try it. Sometimes its something simple like that.. Good luck!
#12
Quote by Roc8995
Sounds like a dirty tube socket. Pull all the preamp tubes out and fire the amp up (you won't hurt anything).
If the buzz is still there, put them back in one at a time, starting with the ones closest to the power tubes. You ought to be able to determine which tube or socket is bad.


Yeah, I wanted to try that but I can't reach the two inner preamp tubes without taking the actual amp out of the case, and when I tried it I found out the bottom of the actual amp is exposed so I decided it'd probably be for the best not to take it out again.

Are there any tricks for this besides doing what this guy did http://www.youtube.com/watch?v=wuQnzM9Q-kk

Quote by surjer
Just a shot in the dark here but have you tried moving your amp to a different outlet or isolating just the amp plugged into 1 wall socket? Sometimes pedal power supplies or well, anything really can cause alot of noise in an amp that your noise gate wouldnt eliminate. My guess is the fellow's above are right in that its something to due with a dirty tube socket or something but definately if you havent tried a different outlet or isolating it, try it. Sometimes its something simple like that.. Good luck!


I also wanted to try that but I wont be able to move it for a few days.
#13
You've already tried cleaning the sockets but you are talking about that hiss in the background, yes? That could easily be coming in from the mains. The mains can have all sorts of crap over it and higher frequency noise won't be filtered out by the power supply caps.
What I'd try is a 0.047uF capacitor between neutral and earth where it comes into the amp from the wall, ala old Fender.
Try it in a different house.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Feb 5, 2012,
#14
I had a wierd noise problem on my peavey classic 50 which turned out to be an output valve, replaced a pair of them as a matched set and it was cured. I think sometimes it is the simple answer that works.

Anyway +1 on a valve being a good possiblity.