2. amps-preamps
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Tube Amp Hum

I have a new VTL ST-150 for about two weeks now. Its breaking in nicely, but one thing I notice with this amp is a slight hum through the midbass drivers. Not audible from the listening position, but there nonetheless. I have the amp on a dedicated 20 amp circuit which was quiet as a mouse with the SS amp that was on it before this amp, which eliminates it being a ground loop. Also, all tubes are all seated properly.

So my question is, is this a normal operating characteristic for a tube amp? If so, does it have a degrading affect on the sound? I would like to hear just pure air when my equipment is on like I had before if possible.

thx!
jc51373
newbee
4,751 posts
 
Some light humming from a tube amp with your ears at the speaker is not unusual. Some are dead quiet, some are not. Occasionally it can be from tubes or currect. You might try a cheater plug and see if that changes the hum (I assume all of your stuff is not on the same line (?). You might also check your connecting IC's to insure they are not too close to other electrical devices, including the amps themselves and power conditioners etc. If you can't hear the hum when you're standing a few feet from the speakers it shouldn't really affect the sound, except mentally by us anal types. :-)
tarsando
578 posts
 
Depends on the efficiency of the speakers
jc51373 OP
518 posts
 
Thanks Newbee...Yes it is when I am at the speaker only that I can hear it, not from the listening position which is only about 8 or 9 feet away. I moved my ICs around a bit and there was no effect whatsoever, and they are shielded (97% according the manufacturer).

The sound is definately not that famous buzz noise which is usually associated with ground loops-which I have chased in the past. This is more of a hum, like a current flowing noise (IE transformer). Also, when you power this amp and the room is quiet you can hear it's initial draw. Kinda like a faint wuuuuunnnnnnhhhuuuuuunnnnhh noise. Bad description I know, but hopefully that describes it.

Outside of listening AT the speaker there is no noise, but where I am new to tube amps and experienced with SS this noise is new to me. If this is normal I can certainly live with it because the amp sound phenomenal. I just prefer to hear that delicious airy sound when my equipment is powered up.
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