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TheNinja

Lifer
Jan 22, 2003
12,207
1
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So I have a Marshall vs65r amp. It's a 65watt amp with a single 12 inch speaker in it. Solid state power amp and a tube preamp. Whenever I have this on now I get a sort of hum. Almost like it's a ground hum/buzz. I tried different outlets, different guitars and different cables. I've tried a 2 to 3 prong adapter but can't get rid of it. One clue might be that it doesn't start to hum until about 2-3 seconds after I hit the power switch. Which could mean that it has to do with the tube pre-amp warming up and humming. Also note the backside of this amp is open and the wiring from the head to the speaker is in view so something/someone could have gotten back there and messed with something but to my eye the solder and wiring looks in place.

Any help or ideas?

EDIT: Fixed
 
nakedfrog

nakedfrog

No Lifer
Apr 3, 2001
61,772
17,476
136
I don't suppose you've got a tube tester lying around... or a spare tube? Shouldn't cost much to get a new tube just to see if it fixes it, but then you'll have to break it in.
 
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TheNinja

Lifer
Jan 22, 2003
12,207
1
0
Originally posted by: nakedfrog
I don't suppose you've got a tube tester lying around... or a spare tube? Shouldn't cost much to get a new tube just to see if it fixes it, but then you'll have to break it in.
Click to expand...

That's probably not a bad idea. The amp does get hauled around once in a while so it is possible something in the tube got jostled around or broken.
 
nakedfrog

nakedfrog

No Lifer
Apr 3, 2001
61,772
17,476
136
Originally posted by: KMurphy
ground loop noise

Text
Click to expand...

You know, I didn't even think of that obvious question. Does it hum only when a guitar is plugged in, or just constantly?
 
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TheNinja

Lifer
Jan 22, 2003
12,207
1
0
Originally posted by: nakedfrog
Originally posted by: KMurphy
ground loop noise

Text
Click to expand...

You know, I didn't even think of that obvious question. Does it hum only when a guitar is plugged in, or just constantly?
Click to expand...

Constantly. I thought it might be a ground loop but I'm not so sure. I had another Marshall Amp (AVT50) plugged into the same power strip and that amp was quiet as a church mouse. And on that first amp, the hissing/humming is on both clean and distorted channel, getting quite a bit louder on the distorted channel. I would expect some hissing on this channel of course, but nothing like it is doing now. I paid like $275 for the amp so I hate to spend $75 minimum to bring it in and have it looked at and fixed, so was looking for suggestions.
 
K

KEV1N

Platinum Member
Jan 15, 2000
2,932
1
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Does it go away with your hands on the strings?

BTW I have that exact same amp for my practice amp. WEIRD!
 
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TheNinja

Lifer
Jan 22, 2003
12,207
1
0
Originally posted by: KEV1N
Does it go away with your hands on the strings?

BTW I have that exact same amp for my practice amp. WEIRD!
Click to expand...

Interesting you say that. My bass has active pickups and sometimes I get a small amount of hum/hiss but when I touch the strings it goes away. On this amp I don't believe it made much of a different whether I touched the strings or not. It even hummed without a guitar plugged into it. I have a bad feeling it's a copenent issue, or wiring.
 
K

KEV1N

Platinum Member
Jan 15, 2000
2,932
1
0
Originally posted by: TheNinja
Originally posted by: KEV1N
Does it go away with your hands on the strings?

BTW I have that exact same amp for my practice amp. WEIRD!
Click to expand...

Interesting you say that. My bass has active pickups and sometimes I get a small amount of hum/hiss but when I touch the strings it goes away. On this amp I don't believe it made much of a different whether I touched the strings or not. It even hummed without a guitar plugged into it. I have a bad feeling it's a copenent issue, or wiring.
Click to expand...

Yep, I guess first check the wiring, then the tube. It's a 12AX7 I believe. And last but not least if you want to buy mine I'll let it go for $200 :)
 
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thomsbrain

Lifer
Dec 4, 2001
18,148
1
0
yes, the tube is a 12AX7. do us a favor and start it up in clean mode with no guitars plugged in and see if the hum starts right away or if still takes a second to come up. also, turn the master volume to zero, then start turning it up and see if the hum changes at all. if there's no change, it's probably in the power amp, which rules out the tube. if it gets louder or softer, it's probably in the preamp and my first thought would be to get a new preamp tube, which should run about $10 at a musical instruments store.

also, did it always do this or did it just sort of start up? have you tried the amp though any different power circuits (opposite side of you house, or someone else's house)?
 
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TheNinja

Lifer
Jan 22, 2003
12,207
1
0
Originally posted by: thomsbrain
yes, the tube is a 12AX7. do us a favor and start it up in clean mode with no guitars plugged in and see if the hum starts right away or if still takes a second to come up. also, turn the master volume to zero, then start turning it up and see if the hum changes at all. if there's no change, it's probably in the power amp, which rules out the tube. if it gets louder or softer, it's probably in the preamp and my first thought would be to get a new preamp tube, which should run about $10 at a musical instruments store.

also, did it always do this or did it just sort of start up? have you tried the amp though any different power circuits (opposite side of you house, or someone else's house)?
Click to expand...

OK, I start it up with nothing plugged in, no cables or anything. I get little or no hum/buzz/hiss. When I plug in a cable/guitar I start to get a hum. The louder I turn it up the louder the hum gets. When in overdrive mode it is very noisy and humming. You might be right about the tube. When I carry the amp and set it down I can hear something rattle a little. It sounds like the tube is rattling around somewhat. I think it probably got carried around and bumped to much and may have damaged the tube. I'll see if the local music shop has a cheap tube I can try to see if that's the problem. I'd rather spend money on a guitar upgrade (Les Paul is my new dream guitar) as opposed to upgrading or fixing my amp for big $$$
 
Gibson486

Gibson486

Lifer
Aug 9, 2000
18,378
2
0
I had a simailir problem with my old Peavey. A friend of mine replaced the power supply and then it worked fine.
 
S

slickcat

Golden Member
Feb 7, 2001
1,501
0
76
Originally posted by: TheNinja
Originally posted by: thomsbrain
yes, the tube is a 12AX7. do us a favor and start it up in clean mode with no guitars plugged in and see if the hum starts right away or if still takes a second to come up. also, turn the master volume to zero, then start turning it up and see if the hum changes at all. if there's no change, it's probably in the power amp, which rules out the tube. if it gets louder or softer, it's probably in the preamp and my first thought would be to get a new preamp tube, which should run about $10 at a musical instruments store.

also, did it always do this or did it just sort of start up? have you tried the amp though any different power circuits (opposite side of you house, or someone else's house)?
Click to expand...

OK, I start it up with nothing plugged in, no cables or anything. I get little or no hum/buzz/hiss. When I plug in a cable/guitar I start to get a hum. The louder I turn it up the louder the hum gets. When in overdrive mode it is very noisy and humming. You might be right about the tube. When I carry the amp and set it down I can hear something rattle a little. It sounds like the tube is rattling around somewhat. I think it probably got carried around and bumped to much and may have damaged the tube. I'll see if the local music shop has a cheap tube I can try to see if that's the problem. I'd rather spend money on a guitar upgrade (Les Paul is my new dream guitar) as opposed to upgrading or fixing my amp for big $$$
Click to expand...

The rattling sound you are hearing is the spring reverb. Solid state based power amps are known to hum. I had a valvestate marshall that would hum constantly because I was close to it and it was using a solid state power amp. You don't get that kind of hum from a tube amp usually. I know the other amp you tried out also had a soild state power amp but it might be something to look into. It could also be the pickups/wiring on your guitar. I would try different guitars on the amp to see if it's the amp or the guitar. I would also try your guitar on multiple amps both solid state and tube to see if you can reproduce the problem.
 
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TheNinja

Lifer
Jan 22, 2003
12,207
1
0
Thanks for all inputs so far, I'll see what else I can find out. I appreciate the help. A lot of knowledgable people around here.
 
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