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Amplifier Hum Issues - Help!
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Tapeworm
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3rd January 2007
Old 3rd January 2007
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Amplifier Hum Issues - Help!

I was wondering if anyone here could help recommend something for this new problem I am having with amplifier hum.

Yesterday I went to lay some guitar tracks down. My Marshall had this low hum to it when I turned it on. I could hear this slight hum when the standby was on. When I switched from standby to on the hum increased slightly (I had this amp overhauled about five months ago and have only used it about 6 times since then – it worked flawlessly –absolutely quiet). As soon as I plugged a patch chord in and turned up the volume, the hum (accompanied by an electrical squealing like sound) appeared. If I plugged in any powered pedal, the noise would increase dramatically. I tried changing speaker chords, patch chords as well as the socket that the amp was plugged into. This has never happened before. Recording equipment seemed fine.

On a hunch, I decided to try another amp or two because the electrical hum sound was nothing like I had ever heard before. All of my amps were humming slightly (the fenders hummed less than the Marshall possibly due to the gain structure but they had all been almost silent before yesterday).

I unplugged just about everything in the studio but the amps still hummed.

I called guitar center (it was 8:00 and I was desperate) and they strongly recommended this Monster “power conditioner” to remove the hum. They said it could happen at any time (10 years and this is a first for me). I flew down there to get it. It did nothing.

Does anyone here have any suggestions for getting rid of this noise? This hum seems electrical in nature and related to the power coming into the house as well as the gain structure of the amp. It does not seem to be a problem of the amp itself and two of the four amps tested have been fully serviced within the year and have worked flawlessly since then.
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3rd January 2007
Old 3rd January 2007
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Let me say from the get-go that any product from Monster will be BS-factor ten!

Is there something wrong with the wiring in the room you are using? Try a different room.

The next step for you is to take the amp with the most hum and the amp with the least hum to a place where there is clean power and try them out (friend's house? Relatives? Work?).

If the hum is only in one room of your house or one part of the house, then there is something wrong with the wiring, though off the top of my head I cannot think what that might be (appart from dangerous that is - particularly if earth or return has lifted a leg'!) If the hum is only at your house, but everywhere else the amps are OK, then there might be a fault at the local step-down transformer. To test this, you will need someone with an oscilloscope who can look at the sine wave of the incoming current and see if there is some issue with it.

Of course, if the amps hum, no matter where you try them out (and they are propper tube amps and not some digital / solid state things), adjust the hum balance on them!!!
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Tapeworm
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3rd January 2007
Old 3rd January 2007
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Yeah...I think the Monster thing is total BS and I'm taking it back after work today. They caught me at a weak moment.

These amps have been used in my studio for years w/o any problems. They have also been used at other peoples houses (and studios) as well. I did not try them in any other rooms but the studio outlets are split between several breakers. I am wondering if some sort of magnetic interference (from what I don't know) could be causing this effect.

I have heard of cellphones causing strange problems (intermittent clicks and static) but mine was not in the studio at the time.


This is driving me mad!
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3rd January 2007
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Usually, when tube amps hum, it is because the caps in the power supply are old and dry and allowing a little AC to come into the DC side of things. If they are all doing this, then that seems unlikely!

Some amps still use rectifier tubes and if that has blown or is weak and that too can cause this problem.

Assuming that the wiring is OK and up to standard - and I have seen wiring in brand new houses that have had the lights wired up by a contractor using telephone cable - I kid you not!!! - then this could be some kind of mains issue.

Cell phones do not create 60Hz hum! Is it a 60Hz hum BTW? (Guitar tuner shows a VERY flat B). If you are in a 50Hz country, then it is a VERY sharp bottom G.

But a regular tube amp will have problems with a VERY uneven power supply, that semi-conductor stuff does not suffer from. That is because computers and audio stuff all have regulated PSU that filter out all RF and knock the voltage down to an exact DC value (which is why nobody needs power conditioners). Have you checked the voltage? Does your mutimeter show 110V (or 220V or what ever it is supposed to be)?

If you do not have a multimeter, now is a good time to go down to Radio Shack or similar establishment and get one! A good multimeter has 1,000 uses!

But assume nothing!!! Have you tried these amps out in someone else's house that is on a different transformer (i.e. NOT the neighbour) AFTER you tested them in your place and found them to be buzzing?
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3rd January 2007
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And before you do anything, is the hum there when a guitar is plugged in using an ordinary MONO guitar cable with NO effects plugged in and NOTHING ELSE is plugged into the amp such as a line to the desk or something?
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3rd January 2007
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The hum is there at a very low level without anything plugged in. As soon as you plug in a patch cord the hum increases slightly. Waving the patchcord around produces an "interference" buzz and occasionally increases the hum a bit (not normal for this amp but it has happened in a few clubs due to lighting). Going near a socket with the cord, especially with a pedal plugged in (but not connected to the amp) increases the hum substantially.

Turning the volume up causes this strange hum to increase. Plugging in a pedal or two into the amp makes the sound unuseable as the hum increases and a static like sound also comes out.

This amp was recapped in March or so and has only been played about 6 times since then. It has been dead quiet since the recapping (the bias was checked as well).

The strange thing was that my other amps have just begun to hum (slightly) as well. My Champ was recapped and retubed in June and has seen quite a bit of use and had been working great until yesterday. I was also using my Twin for ten or so scratch tracks and it never sounded better. Now it too has developed a strange low level hum when turned on.

Right now I have to believe that it has something to do with the incomming power but I really can't imagine what has changed over the last two days.

I had the studio rewired about 6 years ago. Never ever had a problem.

I just spoke to someone and they recommended that I try a ground lift plug.
I do have a multimeter but haven't used it yet. Maybe after I take that Monster crap back to Guitar Center.

I have an old solid state Thomas Organ ungrounded Vox amp that I might try first to see if the hum is also affecting that amp as well (don't worry...I used to play this thing out live all the time a few years ago so I am aware of the shock factor).

BTW - thanks for the help so far
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3rd January 2007
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GROUND LIFT PLUG ?????
never forget it its hazardous and downright deadly do not lift mainsgrounds!!!!!!!!!!!

have you plugged anything else or new into your system or mains in the last few days? or howabout you unplug everything else and see if the hum on the amps is still present .......?
it could be that another piece of gear is causing it?

"any friend that recomends a ground remover is after your wife "
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3rd January 2007
Old 3rd January 2007
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Quote:
Originally Posted by Bassace View Post
GROUND LIFT PLUG ?????
never forget it its hazardous and downright deadly do not lift mainsgrounds!!!!!!!!!!!

have you plugged anything else or new into your system or mains in the last few days? or howabout you unplug everything else and see if the hum on the amps is still present .......?
it could be that another piece of gear is causing it?

"any friend that recomends a ground remover is after your wife "
Only monitors...although, I did get a yamaha aw4416 that I never used to record the Marshall before AND when I tested the other amps, the Marshall was still plugged in.

That old Vox has given me many a surprise over the years. I still turn it on with my sleeve over my hand.
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3rd January 2007
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just a thought
is your studio connected to the house or shared with any other mains facility...office?
could be something outside your control is the prob
cheers
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3rd January 2007
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Do NOT lift the ground, especially in this case! If the buzzing is coming from a poor return path and the amp is using the ground as return, except that it too is not too clever, then the moment you touch it, you could be the new return path for the mains.

Most 'power conditioners' are simply boxes with various devices to trap and remove spikes and other interference from the mains supply. They don't provide safety isolation and they don't in any way alter the mains supply... but they can prove useful if you are having trouble with mains-born interference. But mains hum does not usually come from mains born interference. The trouble is that most interference isn't actually mains-born at all, it is RF (radio freaquency)interference that finds other ways into the equipment.

By offering you a power conditioner, the salesman was giving you incorrect advice for a problem that may even be a safety issue.

Assuming that the amp does not hum-buzz in another house on a different supply, but that all amps are suffering this problem, here are some possible things that could be wrong.

1. the mains lead used with the amp is broken or has had the earth disconnected

2. the earth in the mains distribution/plug-boards/fuse box is broken or has been disconnected

3. The mains earth in the wall socket is faulty.

4. The earth for the whole house - apartment - whatever (tent?) has become faulty (this can happen if someone used a water pipe as an earth and the plumber came and replaced a section with modern plastic piping).

5. You are using stereo jack cables or the cables you are using are faulty.

6. The step-down tranformer in your area is not providing a clean sine wave (most unusual!) or is giving a you completely the wrong voltage (possible, but should not result in the effect you describe).

7. There are lighting dimmers nearby and the thyristors are not suppressed properly and therefore cause this buzzing. (They would have to be mighty dimmers to do that - we have 16 dimmer packs in the studio for video lighting and they certainly do not effect the valve amps like that - but it is possible if they are not supressed.)

Do a quick check on the mains voltage with that multimeter of yours - then I would look at faulty earth/ground first, followed by the faulty dimmer pack in a lighting dimmer. Check the earth by running a cable from the metal chassis of the amp to a known good earth, such as a metal support in the house or a metal rod pushed into damp ground outside. If the problem then vanishes, you get an electrician - fast!
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3rd January 2007
Old 3rd January 2007
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Thanks guys. I have a bad feeling that this problem may be in the house. Nothing is connected to it. I will check into this later today by testing the plugs.

I also have a friend who is an electrician and will check out everything for a few cold ones. Perhaps the problem is in the fuse box. I'll find out later.

Thanks also for the tip on the ground lift.

Byre...can I live in your studio? What a gorgeous place!
#12
18th January 2007
Old 18th January 2007
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Any update on your issue?

I have a buzz problem myself, and was wondering if you were able to fix your situation.
#13
18th January 2007
Old 18th January 2007
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awebagar is offline
maybe used for all

if the AMP HUM...i found the problems oneday..dont PUT your D.I box or RED box lay down
on the top of HEAD AMP. put it on the floor..i think that's the problems..
sorry about my english,..
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