# High pitched whine - Vox AC4TV



## Duster (Dec 28, 2007)

My main amp is a little Vox AC4TV. It's more than loud enough for my little practice room, and I have loved playing it for about 3 years now. It's generally quite silent, and I play a strat-style and an LP style guitar through it, with a drive and delay pedal.

Yesterday, I was playing the LP-style guitar through it, and decided to turn up my drive pedal to get some high levels of gain/distortion. It sounded great, and I played for about 15 minutes at that level.

When I turned everything back down, the amp had a high-pitched whine to it. Turning the volume up and down affects it a little bit. Turning the tone knob up and down affects it a little bit. But even at low volume and low tone, there is this constant whine.

I thought it might be interference from some other electrical device, but I think I've turned everything off. Besides, I didn't change anything - computer, lights, etc. And this high pitch definitely wasn't there before.

I've tried both guitars, same thing. I've turned it off and on a couple of times, it hasn't gone away. When I let the amp cool down, and then turn it back on, it isn't there, but after about 20-30 seconds, when the amp warms up, it comes back.

I don't know anything about how amps work. Could this be a tube that needs replacing? Could I have damaged the speaker playing at high volume / high gain?

Is this a common thing? I don't think I can live with it - it's just there, constantly, and loud enough to give me a headache.

Thoughts or advice?

--- D


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## jb welder (Sep 14, 2010)

It could be a microphonic preamp tube. Remove the preamp tube shields if it has them. Lightly tap on the preamp tubes to see if it has any effect on the whining (careful, they may be quite hot).


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## Duster (Dec 28, 2007)

jb welder said:


> It could be a microphonic preamp tube. Remove the preamp tube shields if it has them. Lightly tap on the preamp tubes to see if it has any effect on the whining (careful, they may be quite hot).


2 stupid questions:

1. I do that with the power connected and amp plugged in? Risk of electrocution?
2. How do I know which tube is the preamp tube and which is the power tube? (this amp has one of each)

--- D


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## bcmatt (Aug 25, 2007)

Duster said:


> 2 stupid questions:
> 
> 1. I do that with the power connected and amp plugged in? Risk of electrocution?
> 2. How do I know which tube is the preamp tube and which is the power tube? (this amp has one of each)
> ...


Yes, do it with everything on, and the amp turned up.
The preamp tube is the little one.


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## gtone (Nov 1, 2009)

Use a wooden pencil or chopstick to tap on the preamp tube - they're about the perfect size/weight and material to do the job safely. You should be able to hear the tap, but if you hear anything beyond the initial tap, you've got a tube that likely needs replacing.


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## Duster (Dec 28, 2007)

Will give it a try tonight. Watch this space. If you don't hear from me, I'm in the hospital with electrical burns.

--- D


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## Duster (Dec 28, 2007)

Thanks for the advice, guys. Turns out there was nothing wrong with the amp. My drive pedal (a Hydra Liquid Gain) has a knob for high and low frequencies. I discovered that if the "high" knob is turned to its upper limit, it introduces an audible but very high whine. Backed it off a bit, and it just disappeared. Embarrassed I didn't think of that last night, but happy I don't have to exercise my feeble electrical skills tonight.


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## bluesguitar1972 (Jul 16, 2011)

If I'm playing too loud and hear a high pitched whine, I usually first check the girl-friend. 
Glad you got it sorted out though.


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## Duster (Dec 28, 2007)

bluesguitar1972 said:


> If I'm playing too loud and hear a high pitched whine, I usually first check the girl-friend.
> Glad you got it sorted out though.


Nice one. That even got a laugh from my wife!

--- D


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