How much noise is "normal" from a tube amp

[RedStangMan]

I bought my first tube amp, a Marshall AVT 50 combo, and am wondering if the amount of buzz and hiss I am getting is expected. It's hard to describe an amount of noise but it is more than I would expect once I get up to around 1/2 volume on the overdrive channel, more buzz if gain is up too. The clean channel isn't quite as bad until around 3/4 volume.
I've also found a more annoying buzz with my Jackson JS-20 plugged in. That buzz goes away if I touch the volume control on the guitar.
Thanks for any advice!

[cminor9]

Depends. Noise can come from a lot of places. Here is how you figure out where the noise is coming from: turn everything up, and turn down knobs, one at a time. Whichever knob kills the noise, that means the noise is before that knob. If you turn down your guitar vol and the noise goes away, for example, then it's your guitar.

Also, it is normal to hear a slight buzz if you aren't touching the guitar strings or bridge, or something.

Are you playing in a room with fluorescent lights or a dimmer switch? Single coil pickups? Those are all potential sources of hum.

[Enzo]

How long is a piece of string?

Unplug the guitar from the amp. We want the amp just sitting there with nothing plugged into it. Now how much noise does it make?


Now plug the guitar into the amp - straight in, no floor toys - but turn the volume control on th guitar down to zero. Is there any increase in noise?

Those two steps reveal the noise of the amp itself. Any additional noise that comes when the guitar is turned up from zero is not coming from the amp, but is coming from the guitar.


The more gain there is, the more noise there will be.

[diagrammatiks]

that's not a tube amp

[JHow]

The amount of noise coming from an amp correlates inversely to the skill of the guitarist.

[Raybob]

Using a SPL meter right on the grill cloth, with 2x6L6s, 52db is nice. with 2x6V6s, 50db. FYI: I measured a friend's Fender Custom Vibrolux re-issue and got 56db. The numbers above are from my builds. Funny, I go to extremes, separating power grounds from pre-amp ground bus with isolated reverb jacks, etc. I also own a stock 68 Fender DR with brass plate ground, chassis grounds etc. That thing is 1 db quieter (49db) than one of my DR builds. Makes me wonder if all my grounding separation tricks learned from internet geeks, over all these years, wasn't all in vain.

[cminor9]

Using a SPL meter right on the grill cloth, with 2x6L6s, 52db is nice. with 2x6V6s, 50db. FYI: I measured a friend's Fender Custom Vibrolux re-issue and got 56db. The numbers above are from my builds. Funny, I go to extremes, separating power grounds from pre-amp ground bus with isolated reverb jacks, etc. I also own a stock 68 Fender DR with brass plate ground, chassis grounds etc. That thing is 1 db quieter (49db) than one of my DR builds. Makes me wonder if all my grounding separation tricks learned from internet geeks, over all these years, wasn't all in vain.

I don't know if I'd call separating grounds all that extreme. But the isolated jacks, well...

[RedStangMan]

that's not a tube amp

It has a tube preamp. The power stage is solid state.

[Ronsonic]

I bought my first tube amp, a Marshall AVT 50 combo

Not a tube amp. It's a SS amp with a tube in it.

Now, about this noise .... Read Enzo's post number 3. Pretty much everything I would say on the subject.

Then why am I posting, 'cause too often the right answer comes up early in a thread and gets overlooked.

[RedStangMan]

How long is a piece of string?

Unplug the guitar from the amp. We want the amp just sitting there with nothing plugged into it. Now how much noise does it make?


Now plug the guitar into the amp - straight in, no floor toys - but turn the volume control on th guitar down to zero. Is there any increase in noise?

Those two steps reveal the noise of the amp itself. Any additional noise that comes when the guitar is turned up from zero is not coming from the amp, but is coming from the guitar.


The more gain there is, the more noise there will be.

The amount of noise appears to be virtually the same with or without the guitar plugged in.
With the gain all the way down it's more of a low frequency hum. As I increase the gain it adds a sort of overtone hum. I'm guessing that's normal since over-driving an amplifier clips the input signal creating harmonics (if I'm remembering anything at all about amplifier circuits).

[tubeswell]

Apart from doing what enzo said, did you try swapping out the tube? (Occasionally some tubes are 'noisy')

[tedmich]

Nothing BUT noise comes from my amp:

"I play GUITAR, I don't play MUSIC"