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Old 04-21-2013, 04:03 PM   #1
Gillthenasty
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JCM 800 hum?

Hi!

I'm playing a p90 guitar through a JCM 800, and I get a hum from the amp.
Is this normal? I'm kind of new to tube amps, so I can't tell from own experience.
(From what I can remember, I only get the hum on high sensitivity.. Well I barley play low sensitivity )

Thanks
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Old 04-21-2013, 04:06 PM   #2
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Is the amp used?
are the tubes new?
how loud and how close are you to it?
Does the sound stop if you mute the strings?
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Old 04-21-2013, 04:12 PM   #3
MaggaraMarine
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Do you have another guitar (with humbuckers)? P90s are single coils so you get more hum with them than with humbuckers.
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Old 04-21-2013, 04:22 PM   #4
Gillthenasty
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The tubes were said to be from 2010 or so, but used a very few times. (The amp is used but I bought it just a few months ago)
I'm basically as low as you can go on the JCM 800.
I do not think the sound stops if I'd mute the strings, but I'm not sure. I'll try the next time I'll play it.

I do not have any other guitar with humbuckers at the place where the amp is, but I have a stratocaster from 74 with very low distortion in its single coil pickup. I can try with that one.

I might just bring it in for a quality check, since I don't know what else could be worn out or such.
What do you say?
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Old 04-21-2013, 04:29 PM   #5
MaggaraMarine
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Strat pickup position 2 and 4 should be hum cancelling, and I'm not sure if both p90 pickups selected at the same time cancels hum. And your amp can have bad tubes even if they are new.

But don't spend any money on it before you know what causes the problem. Because if it's your guitar, power outlet, cable, whatever, you will just waste money.
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Old 04-21-2013, 04:39 PM   #6
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If you're new to valve amps, I wouldn't worry. You're probably used to solid state amps, which have much less background noise. Valve amps, even when working perfectly and used with humbuckers, generate some additional background nosie that solid states don't. THe higher you turn the gain, volume, middle and treble controls, the more you'll hear that noise. This is in addition to whatever nosie might be coming through from your guitar and/or pedals. P-90s are a giant single coil and have louder 50/60-cycle hum than any other type of pickup, so that's one reason while you'll be getting a lot of noise. Cheaper cables, cheaper pedals and any kind of boost/OD/distortion/compresson pedal will also increase how much noise you get.

You can buy noise gate/suppressor pedals quite cheaply that will take care of any noise from the guitar and you can get others which are suitable for putting in an amp's effects loop to quieten the amp's noise, if it does have a loop. Don't be tempted by noise pedals that seem like they can lessen noise both from the guitar and the amp, because the reality is that the noise from the guitar is quite different to the noise from the amp and the two need to be handled differently, not by just one unit.

But generally, using hum-cancelling pickups, less treble, less gain, higher-quality cables and standing further from your amp will help reduce noise. There will always be considerable hum when using P-90s. Never expect a valve amp to be completely silent, it's just not int heir nature; any noise reduction that totally silences the amp will also greatly effect your playing dynamics and the overall sound of the amp.
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Old 04-30-2013, 03:18 PM   #7
Gillthenasty
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Hi again!

I'm finally back with more information.

I plugged a stratocaster with barley no dist in and there was still a hum, but it small quieter but didn't stop when I muted the strings.

Is this normal? Is this info usable?

thx!
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Old 04-30-2013, 03:33 PM   #8
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Single coils hum. P-90's and strat pups are single coils. It is normal.
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Old 04-30-2013, 04:48 PM   #9
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Did you try the middle positions?
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Old 04-30-2013, 05:13 PM   #10
MaggaraMarine
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Quote:
Originally Posted by Gillthenasty
Hi again!

I'm finally back with more information.

I plugged a stratocaster with barley no dist in and there was still a hum, but it small quieter but didn't stop when I muted the strings.

Is this normal? Is this info usable?

thx!

Again try different cables and pickup positions. Positions 2 and 4 should be more silent than the other positions. Also we don't know how loud the hum is and how it really sounds like. You should post a video. Amps do hum but if it's too loud hum, it's not normal. But we can't tell if it's too loud or just normal hum unless we see a video or something.

Try it with a humbucker equipped guitar and try it with Strat pickup positions 2 and 4. Try different cables!! Also plug your guitar straight to the amp without any effects in front (or in the FX loop).

Also try different power outlets. Maybe try the amp at your friend's house (if possible) and see if the hum is still there.
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Old 04-30-2013, 10:01 PM   #11
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Is it only when you get really close to the amp or even when just facing a certain way? If so, that's pretty normal. I play extremely loud and it can even be an issue with humbuckers but when I'm playing my tele with single coils it's ridiculous. Whenever I am playing the tele I have to be very careful where I stand. My amps are quite quiet normally (I'm a bit of a nazi when it comes to that) but if I stand in the wrong spot it takes off.
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Old 04-30-2013, 11:55 PM   #12
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My amps are quiet as a mouse even when cranked so even a little bit of hum would bother me because I'm not used to that.

The first thing I would do is take the amp to a different room in your house and then a different house altogether and see if there is any difference. Then try different cables and stand close and then far away like Cath is saying. Take out all other pedals etc. Play with the lights turned off and other appliances off. Then I'd experiment with some different preamp tubes (start by swapping around what is in there now and leave the power tubes alone - the big ones).

That doesn't cost you anything.

It is really hard for us to tell thought because we can't hear the hum. If is more than say TV volume or talking volume then I'd take it to a tech for a once over.

Get an estimate first of what they are going to do and make sure they detail out for you what they do do. Tell them you will be sharing what they do with people online. Don't let them screw you over. Far to often I see places charge $50 just to bring it in and then the first thing they want to do is sell and install new tubes. 7 days later you've spent $200 and the amp sounds the same.
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Last edited by 311ZOSOVHJH : 05-01-2013 at 09:15 AM.
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Old 05-01-2013, 01:39 AM   #13
ibanart300
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Didn't see this suggested but do you get hum when you have nothing plugged in? I had a similar issue on one of my amps and it wasn't the cables or the guitar but one quick way to start narrowing it down it just to turn it on and raise the volume without your instrument plugged in. My issue turned out to be a simple faulty filter cap in the end but anyway just thought I would suggest it.
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