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-   -   Amp just started making this weird new sound!!! (http://metaltabs.com/forum/showthread.php?t=17101)

neuromonkey 2005-01-10 15:17

Amp just started making this weird new sound!!!
 
I had just gotten a friend's VH-140c head cleaned & fixed up a bit when the damned thing started making this very odd sound--

Imagine a bee flying back and forth, diving past your head. It's doing this over and over at around once a second, or slightly slower. Bzzzwww... Bzwww..Bzzzzzwww..-- NOT regularly timed. Continuous, but erratic. Then it'll stop for a couple of minutes. Then start for another 10 minutes...

The sound _almost_ entirely vanishes when there's nothing in the input jack, but I can still hear it in there with the gain & volume cranked up. It *does* appear to be in the amp, and not a cable or my bass or the AC power or fluorscent lights. It's such a weird thing that I'm going to post a .wav file of it for people to listen to.

It seems to start about 2 minutes after the amp is turned on. The only thing I can think of is maybe it's some capacitor discharging into the signal path...? It's the same in both channels and in both speaker outputs. None of the controls or effects seem to impact whatever is causing it. It really does sound like RF interference, but I've powered down everything else, and the amps position doesn't seem to matter.

Anyone have any ideas of what I might try? Replace caps maybe? Could it be the transformer? ARGH! Listen to a short snippet of it, at...

http://radhack.com/dump/killerbee.wav

In this recording it's pretty regular, but it usually speeds up & slows down for no reason that I've been able to discern.

Thanks all!

Soulinsane 2005-01-10 15:29

Welcome.

And that is one of the wierdest things I have ever heard in an amp. Seems that you have eliminated the likely sources. I'm a electronic tech and I have never heard anything like that. It is something like you said in the signal path, and I think it is in the power amp side. A capasitor discharging could be the problem, like you said, if it is being shorted by dirt. You siad that you cleaned it. Well you may have knocked some dirt lose into the amp. If you clean the insides make sure you fully discharge the amp first so you DON'T kill yourself. If I don't here from you again I will asume you died while cleaning the inside of the amp.

So your first step is to clean and inspect the inside of the amp and we will go from there. Do you know how to discharge the amp?

guitar_demon 2005-01-10 16:09

could it be a signal from another electronic devise in the house?
i know sometimes if im playing and my dad has a saw going in the garage when he turns it on i can kinda hear it through my amp

Overmind 2005-01-10 17:25

Maybe there's a bee trapped in your amp.

Mordor 2005-01-10 17:49

hahaha, a bee lol, its probly interferance from somet in ure house, eg mobile phones, radios etc

BLS 2005-01-10 17:57

Wow... thats not pleasant.

Definetly sounds like some AC noise, try plugging your amp into a power strip.

Or contact JerryP fjamods@aol.com He usually dosent work with Ampeg's but he knows what he's talking about and im sure he can help narrow down the possible issues.

*insert name here* 2005-01-10 18:23

yeah but if the noise stops when you take the cable out,maybe its not the amp,and the noise when you turn up the volume and gain,even with the cables out might just be the usual feedback.maybe its the cables or your pickups?hope this helped.

John Holland 2005-01-10 19:55

There is only one solution : It must be taken to the priest to be exorcised.

guitar_demon 2005-01-10 20:00

*waits for the amp to vomit*

John Holland 2005-01-10 22:36

We must douse the amp while turned on ( to make certain that the demons are commencing their vile activity ) in a vat of blessed holy water ... if the amplifier continues to operate, then it is indeed demon-possessed and must be destroyed. If the amp ceases operation, then it has thus become free of malicious influence and it may be returned to the owner.

neuromonkey 2005-01-11 02:22

Discharge me, baby
 
> you may have knocked some dirt lose into the amp.

Yeah, I'm going to go over it again and see if I can whack anything loose. Seems weird, but I suppose I could have wedged something somewhere.

> If you clean the insides make sure you fully discharge the amp first
> so you DON'T kill yourself.


Sure, yeah. I think I'm supposed to touch the anode with one hand, and the cathode with the other, right? And to test to see if a capacitor is holding a charge, I lick the leads briefly. As long as I'm quick about it, the electricity can't get inside me where I'm all soft and squishy. Like in my head.

Naw, I know. I'm not as cautious as I should be, but I do know the right way to discharge a cap. I've done stage lighting using 600v, and numerous other really inadvisable electrical projects, and I'm not dead yet. I'd be pretty embarassed if a tiny little capacitor got me.

> could it be a signal from another electronic devise in the house?

It's *possible*, but I don't think so. I powered down my computer and all other audio gear. If it is a device in the house, it's something that's putting out a strong signal.

I tested the amp powered from an uninterruptible power supply, and that's supposedly completely isolated from the house current. Yeah, power tools do inject an enormous amount of noise into the house wiring. I have a cordless phone, but no cellular or other wacky radio devices. Also, the sound doesn't change when I move the amp. If it were RFI, I would expect the sound to change as the amp moved around through the signal. I'm pretty sure it's coming from somewhere on-board.

> Or contact JerryP

Thanks. If I can't find the problem in a couple of days, I'll do that.

> if the noise stops when you take the cable out,maybe its not the amp

It gets waaay quieter, but doesn't go away. I tried several different cables... Actually, you know what? I didn't try different _speaker_ cables. Those could be insufficient, and causing problems that way. Hm.

> *waits for the amp to vomit*

It does that shortly after I begin playing.

Thanks, everyone, for the good ideas. It's good to bounce stuff like this off of other people, even if the most practical advice does involve the casting out of demons from a solid state device. You'd think that Satan would be more of a tube amp kind of guy.

Sorry about the dead link to the sound file. Stupid clerical error, hopefully fixed tomorrow. I'll post as the story unfolds. The Demon Bee That Ate My Amp. Gripping stuff.

neuromonkey 2005-01-11 17:33

No more bee.
 
Huh. Well, I wish I could say that it was due to my overwhelming skill and knowledge, but I turned the amp on today, connected it to a couple of speakers (instead of the one I was using,) and it's totally quiet.

Hm.

Perhaps I'll never know.

*insert name here* 2005-01-13 05:50

Quote:
Originally Posted by neuromonkey
Huh. Well, I wish I could say that it was due to my overwhelming skill and knowledge, but I turned the amp on today, connected it to a couple of speakers (instead of the one I was using,) and it's totally quiet.

Hm.

Perhaps I'll never know.


then doesnt it mean that it came from the speakers?anyways good news! :cool:

Soulinsane 2005-01-16 22:00

You find the problem yet?

Party Time 2000 2005-01-19 11:30

I'd like to know how to discharge an amp, Soulinsane.

I don't like the "lick" method mentioned above. :p

BLS 2005-01-19 17:52

Just turn your amp off and let the caps discharge for an hour or so.


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