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
jc51373 OP
548 posts
 
Correction now that both my wife and I listened for it. It seems louder out of the left channel than the right, and....It is faintly audible from the listening area, not just at the speaker.

I gotta tell ya, if there is way to resolve this noise I would love to know. I am not one for noises of any sort from my audio system.
thorman
1,262 posts
 
Could it be from your cable tv provider? Many have had problems with cable tv and stereo system using the same eletrical lines...Or possibly your refrigerator...Just 2 thoughts.......Good luck
newbee
4,794 posts
 
Reverse the tubes - and see if the sound follows the change or remains constant. Reverse the small tubes first - if the left channel is still a bummer, try the power tubes next. If that doesn't help call VTL. I have amps which hum a bit, but its the same in both channels - so if its not the tubes it may be a bad part in the amp which needs to be replaced.
jc51373 OP
548 posts
 
My refrigerator? Definately not....The system is on a completely dedicated circuit, there is no cable system on this circuit whatsoever. It is not a ground loop.

Newbee, I will try the tube reversal as you mentioned. Sounds like an idea.
jw94055
125 posts
 
I know this sounds left field, but try different cables from your pre to power amp. I have a tube pre and ss power. I bought some high end cables and they produced a buzz. Replacements were tried with the same result. Put in old generic cheapos and the buzz went away. I would make sure the shielding on the interconnects is plenty thick. Again, this is one person's suggestion.
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