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matskull
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#1
25th June 2009
Old 25th June 2009
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Tube amp noise

Hi everybody,

I recently got a vintage marshall jubilee, it sounds awesome but it's a bit too noisy.

I tried different preamp tubes and power tubes and it didn't change anything.
The amp is noisy with the guitar's volume turned all the way down.
It's not a hum, it's more like a high pitched electric noise.

The noise disappear if I turn the gain or master down, I red comments from people who own the jubilee and it's supposed to be pretty quiet even at high gain, my mesa is like 75% more quiet than the jubilee right now...

I recorded the fx send and DI output from the jubilee and they are noisy as well.
If I plug a cable into the fx return the noise goes away, I even tried to plug my guitar into the effect return and it wasn't noisy.

This makes me think that the noise is coming from the preamp, I know a little bit of hiss would be normal at high gain but not this kind of noise...

Here's a sample I recorded, at 2 sec I switch the standby to on with guitar's volume all the way down, then at 8 sec I turn the guitar's volume up and play a couple notes and after that I turn the guitar's volume all the way down again.
On the sample everything was at 12 o'clock and the gain was at 2 o'clock using the lead channel.

What do you think it can be?
Here's the sample: http://www.gearslutz.com/board/attac...ilee_noise.mp3
thanks
#2
25th June 2009
Old 25th June 2009
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Sounds like a grounding buzz to me. Might just need to be opened up, thoroughly cleaned of corrosion from behind the front panel. It could also simply be a lead dressing issue. (IE a signal wire laying close to a noise inducing wire)

STANDARD DISCLAIMER:
There are hundreds of volts flying around in that tube amp. When its off and unplugged, it can knock the crap out of you. When it on and running, It could kill you with the electricity inside. Dont crack this open unless you know how to handle yourself around high voltages and know proper discharging techniques.
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26th June 2009
Old 26th June 2009
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Quote:
Originally Posted by Mylithra View Post
Sounds like a grounding buzz to me. Might just need to be opened up, thoroughly cleaned of corrosion from behind the front panel. It could also simply be a lead dressing issue. (IE a signal wire laying close to a noise inducing wire)

STANDARD DISCLAIMER:
There are hundreds of volts flying around in that tube amp. When its off and unplugged, it can knock the crap out of you. When it on and running, It could kill you with the electricity inside. Dont crack this open unless you know how to handle yourself around high voltages and know proper discharging techniques.
Yeah that's what I think too, also if I play around with the speaker cable while the amp is on it seems to affect the noise, so a ground problem could be quite possible.

Anybody else has an idea?
Btw, don't worry, I know what to not touch inside of an amp and anyway I'll have it checked by a pro.

thanks
matskull
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26th June 2009
Old 26th June 2009
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I just did another test.

I plugged my guitar into a mesa boogie tremoverb dual rectifier, then I plugged the effect send of the mesa into the effect return of the marshall and I played my guitar, there was no noise.

Then I did the opposite, plugged the guitar into the marshall, plugged the effect send from the marshall to the effect return of the mesa and there was that same noise that I hear from the marshall...

Nobody has an idea?
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26th June 2009
Old 26th June 2009
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Often, the ground on a "new" amp will take it's ground point on the input from the input jack, instead, take it from the rear plate where the outputs are and you will eliminate that problem.
I have a Marshall JMP 50watt and had this done. It works is all I can say.
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I think I just ran past myself.
http://www.memphisindie.com

I won't use pitch correcting software. I use "coaching" maybe you've heard of it. It keeps working even when you don't have it on.
matskull
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26th June 2009
Old 26th June 2009
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Quote:
Originally Posted by memphisindie View Post
Often, the ground on a "new" amp will take it's ground point on the input from the input jack, instead, take it from the rear plate where the outputs are and you will eliminate that problem.
I have a Marshall JMP 50watt and had this done. It works is all I can say.
I'm not very good in electronic but here is a schema of the jubilee, can you tell if the ground it on the input jac or not?

So did you have the same kind of noise that I have before you did this mod?
thanks
Attached Files
File Type: pdf 25aniv_silverjubilee_25_50w_2550.pdf (190.9 KB, 357 views)
#7
26th June 2009
Old 26th June 2009
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Yes, it is going to the ground from the input jack only.
Yes, I had the same problem.

Mine is now "rectified" and makes no noise, and I can control clean to dirty from the guitar volume pot.

I didn't do the mod, but, I was right there when it was done by none other than Matt Wells.
matskull
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26th June 2009
Old 26th June 2009
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Quote:
Originally Posted by memphisindie View Post
Yes, it is going to the ground from the input jack only.
Yes, I had the same problem.

Mine is now "rectified" and makes no noise, and I can control clean to dirty from the guitar volume pot.

I didn't do the mod, but, I was right there when it was done by none other than Matt Wells.
Cool, looks like something pretty easy to do as well.

I've been suggested that it could be a relay problem which would induce AC leakage into the preamp too, I might try this myself...
I'm no pro to read schema but I usually understand when I see the real thing and I know how to not kill myself when I open my amp so...

So when he took the ground from the input jack and put it on the output jack, did he have to make something special or was the connector for the ground allready there, also did he jump both output's ground together?


Thanks for the info.
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26th June 2009
Old 26th June 2009
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He didn't tie it to the output "jack" just to the rear plate of the amp with a wire and soldered it on.
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26th June 2009
Old 26th June 2009
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Quote:
Originally Posted by memphisindie View Post
He didn't tie it to the output "jack" just to the rear plate of the amp with a wire and soldered it on.
Ah ok, I misunderstood the first time, I get it now.
this is a pretty old school way of doing it isn't it?

cool to know it worked
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26th June 2009
Old 26th June 2009
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From what I understand, it's the first thing a good tech does if he has pro clients who can't be havin that buzz.
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26th June 2009
Old 26th June 2009
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Quote:
Originally Posted by memphisindie View Post
From what I understand, it's the first thing a good tech does if he has pro clients who can't be havin that buzz.
Really, I'll try that.
thanks
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26th June 2009
Old 26th June 2009
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I opened the amp and it doesn't look as easy as I thought, the input jack is mounted to the pcb and when I look at it it seems like it is grounded to the chassis anyway.

here's a pic
Attached Thumbnails
Tube amp noise-img_2569small.jpg  
matskull
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27th June 2009
Old 27th June 2009
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Alllright I did some other tests.

I realized that my input jack is a little bit dirty and the sleeve doesn't close corectly when I there's no cable plugged in, if I push on it a little bit the contact closes and the noise disapear (with no cable in).

Then I started to gently tap on everything to see if I could find a cold solder join, I didn't find any but I found something really interesting.

When I touch and/or move the yellow or the green wire that are on V1 (see picture) the noise increase a lot and it really seem to be the same electrical noise that I hear.

Is the only way to fix this to put bigger/better wires...?
Attached Thumbnails
Tube amp noise-img_2569_arrows.jpg  
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27th June 2009
Old 27th June 2009
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Well, you could try using a shielded wire in those spots, BUT, it would have to be the same gauge on the internal conductor as the wire you are using now. If that wire is meant to be able to pick up proximity like that, shielding it should stop that BUT, it may also change he tone of the amp......or, not. The shield should be grounded on one end too.
Probly not much, might sound better, it's worth a shot.
Don't zap yourself in the process.
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27th June 2009
Old 27th June 2009
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Quote:
Originally Posted by memphisindie View Post
Well, you could try using a shielded wire in those spots, BUT, it would have to be the same gauge on the internal conductor as the wire you are using now. If that wire is meant to be able to pick up proximity like that, shielding it should stop that BUT, it may also change he tone of the amp......or, not. The shield should be grounded on one end too.
Probly not much, might sound better, it's worth a shot.
Don't zap yourself in the process.
I think I'll take it to a tech but at least I'll know what to tell him.

It's weird cause those two wires are the only one to affect the noise...
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27th June 2009
Old 27th June 2009
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Quote:
Originally Posted by matskull View Post
I think I'll take it to a tech but at least I'll know what to tell him.

It's weird cause those two wires are the only one to affect the noise...
It could be completely normal for those two wires to be so sensitive, that's why they make mu-metal and sheilded wire.
Just don't work on it plugged in and discharge the caps with an insulated tool, like a screwdriver, or wait for them to drain completely.
I'll pull mine apart tomorrow and see if I can post a pic to see if there is any big difference. I know Matt handwird the thing infront of my eyes in record time and I have had no problems in 20 years. WOW. That was a long time ago. Still working.
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27th June 2009
Old 27th June 2009
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For the jack input ground though like you can see on the picture there's allready a wire goind to the chassis...
So I think I can't make this any better.
#19
27th June 2009
Old 27th June 2009
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Yeah, that part seems ok.
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27th June 2009
Old 27th June 2009
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Quote:
Originally Posted by memphisindie View Post
Yeah, that part seems ok.
good
thanks
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27th June 2009
Old 27th June 2009
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The lead to the input grid of your first preamp tube will most definitely be very susceptible to noise. This was the lead dressing I was speaking of. Changing the lead to the input grid to a shielded cable and actually making it shorter could help with the problem. Your input jacks are the neutrik plastic jacks (IE, the input ground isnt grounded to the chassis directly through the input jack but Im pretty certain it is by virtue of the pots right next door having direct contact with the chassis.)
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27th June 2009
Old 27th June 2009
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Quote:
Originally Posted by Mylithra View Post
The lead to the input grid of your first preamp tube will most definitely be very susceptible to noise. This was the lead dressing I was speaking of. Changing the lead to the input grid to a shielded cable and actually making it shorter could help with the problem. Your input jacks are the neutrik plastic jacks (IE, the input ground isnt grounded to the chassis directly through the input jack but Im pretty certain it is by virtue of the pots right next door having direct contact with the chassis.)
Yeah I wonder how much of a difference a sheided wire would make...
Cause that noise is annoying, I really hope my tech will know what to do with this.

thanks for the help
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27th June 2009
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I just busted open a fender bass amp I've been restoring, it had the ground much like this one, I just literally took the jack and wired it straight to the chassis and it stopped buzzing at full volume high gain.
There were two jacks tied together, I separated them and put different caps on them for different sound (fat/skinny).
It had one jack (skinny) that buzzed and that's the one I hit. It has two wires going to the tube, no problem with them now.
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27th June 2009
Old 27th June 2009
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Quote:
Originally Posted by memphisindie View Post
I just busted open a fender bass amp I've been restoring, it had the ground much like this one, I just literally took the jack and wired it straight to the chassis and it stopped buzzing at full volume high gain.
There were two jacks tied together, I separated them and put different caps on them for different sound (fat/skinny).
It had one jack (skinny) that buzzed and that's the one I hit. It has two wires going to the tube, no problem with them now.
So you took a cable and wired it from the jack's sleeve to the chassis?
Mine is soldered directly on a pcb, I'm not super confortable to mess with it...

If you have some pictures that'd be great!
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27th June 2009
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Exactly, I took a wire, soldered one end to the sleeve connection and the other end to the chassis.
If you don't feel comfortable, by all means, use a qualified tech.

I'm bad about the pics, but, I'll see what I can do.
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28th June 2009
Old 28th June 2009
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Quote:
Originally Posted by memphisindie View Post
Exactly, I took a wire, soldered one end to the sleeve connection and the other end to the chassis.
If you don't feel comfortable, by all means, use a qualified tech.

I'm bad about the pics, but, I'll see what I can do.
allright, thanks man
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29th June 2009
Old 29th June 2009
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My problem appeared to be in the way the wires are placed, I'll redo the wiring and call it a day.

thanks for the help
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4th July 2009
Old 4th July 2009
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Quote:
Originally Posted by matskull View Post
Hi everybody,

I recently got a vintage marshall jubilee, it sounds awesome but it's a bit too noisy.

I tried different preamp tubes and power tubes and it didn't change anything.
The amp is noisy with the guitar's volume turned all the way down.
It's not a hum, it's more like a high pitched electric noise.

The noise disappear if I turn the gain or master down, I red comments from people who own the jubilee and it's supposed to be pretty quiet even at high gain, my mesa is like 75% more quiet than the jubilee right now...

I recorded the fx send and DI output from the jubilee and they are noisy as well.
If I plug a cable into the fx return the noise goes away, I even tried to plug my guitar into the effect return and it wasn't noisy.

This makes me think that the noise is coming from the preamp, I know a little bit of hiss would be normal at high gain but not this kind of noise...

Here's a sample I recorded, at 2 sec I switch the standby to on with guitar's volume all the way down, then at 8 sec I turn the guitar's volume up and play a couple notes and after that I turn the guitar's volume all the way down again.
On the sample everything was at 12 o'clock and the gain was at 2 o'clock using the lead channel.

What do you think it can be?
Here's the sample: http://www.gearslutz.com/board/attac...ilee_noise.mp3
thanks
If it's a high pitched whine or ring, not a buzz you have a bad preamp tube. Merely swapping tubes with new ones may not cure the problem, as a large percentage of 12AX7/7025/ECC83 tubes have this problem brand new out of the box. They may work fine in a low gain situation such as many hi-fi preamps but fail in guitar amps. The severity of the problem varies acc0ording to the gain of the stage involved. When I was a service tech we had failure rates of approximately 25 to 35% for standard RCA 7025s in the first stage of a stock Fender Twin. This climbed to failure rates as high as 90 to 95% or more in the first stage of a Mesa Boogie MKII. In fact we always used the premium hand selected Mesa branded tube for that purpose due to the extremely high rejection rate.

Failure rates for this application were also MUCH higher in certain brands of tube favored by audiophiles for superior tone - Mullards were pretty bad, Telefunkens were terrible - 90% rejection in a stock Twin. About the only brands back then that worked well for guitar amps were RCA and Sylvania.

I have no idea what the rejection rate is for the current brands of imported tubes, but I can't believe that it's any lower unless you're buying from a company that hand selects tubes for specific guitar amp applications, and that will cost you - but it's worth the extra cost, as tubes are generally not returnable, especially if they test good on a tube checker, which microphonic tubes WILL do, as checkers don't test for noise. The only way to test for noise is to put the tube into a high gain amplifier circuit and listen, and that's pretty labor-intensive.
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4th July 2009
Old 4th July 2009
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Just read the rest of the thread - it does seem to be a ground problem. Seems you have good advice on it already......
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5th July 2009
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Quote:
Originally Posted by John Eppstein View Post
Just read the rest of the thread - it does seem to be a ground problem. Seems you have good advice on it already......
yeah basically it's a wire that was going under the pcb and it was not suposed to.
So just by moving this cable away it solved the problem but I decided to go further and to rewire the preamp section.

I'm just waiting for a new input jack to arrive before I do the job, I'll replace it too cause the sleeve doesn't cut the signal anymore when there is no cable plugged in.
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