2. amps-preamps
  3. 1179751270

Tube Pre-Amp Question

I just hooked up a VTL 2.5 tube pre-amp to my system.
When the volume is off, nothing being played in the CD or other, there is this hum coming from the tweeter in the speaker. It gets louder when I turn up the volume.
What is this?
**I didn't have this with my SS pre-amp.
**Speakers are ML mosaic's. Non electrostat type.

Thanks in advance.
adman227
audphile1's avatar
audphile1
4,919 posts
 
you are probably hearing tube hiss, which is normal for a tube preamp, but it should not go up with volume.
noble100's avatar
noble100
2,419 posts
 
I have the same VTL 2.5 preamp with a SS amp and it's dead quiet even if you put your ears next to the speakers and turn up the volume. The output impedance of the 2.5 preamp is 200 ohms. I've read here on Audiogon that the input impedance of the amp should be at least 10 times this number for a good match, which would mean 2000 ohms or higher. The amp I use has an input impedance of 22,000 ohms. I'm not sure whether this would cause the problem you're describing. If not, then it may be a bad tube(or tubes) or a ground issue.
adman227 OP
22 posts
 
I've been thinking of changing the tubes anyway. People have recommended Telefunken Tubes, and say it's night and day in performance when you do it.
More to discover