2. amps-preamps
  3. 1230921553

Hum in VTL 125 mono block amps

I have VTL 125 mono block amps they are about 11 years old with fresh tubes as of late they produce a hum or buzz in the speakers that they never had . Nothing in the system has changed , I get the hum- buzz even with the pre amp muted the level of buzz- hum does not change even when I un mute the pre so I think the hum -buzz is from the power amps. All eq is on a dedicated 20 Amp line cables are top of the line Ridge Street Audio power cables and Ridge Street poiema 3 IC'S / speaker cables. Do any of you have a idea what to ck is a cap starting to leak due to age or something else. Marc
lake513
mrtennis
3,295 posts
 
is it possible that you can try a different amp ?

although probably a waste of time, you could change the power cords and or use cheater plugs.
lake513 OP
123 posts
 
Katylied ; Good idea , I have tried one amp at a time still the hum I will try a different cable later today. Mrtennis ; Thanks for the idea I will try both things later today a different amp not possible right now but may be able to try that later Thanks Marc
newbee
4,768 posts
 
Couple of other things to try...

1) Disconnect the amp from the pre-amp, muting may not be enuf.
2) Makes sure that all unused PC's are disconnected from outlets (believe it or not another hum I had was sorced to exactly that!).
3) If that fails, bite the bullet and disconnect and unplug everything and start from scratch. One amp to one speaker, then the other, then both together, then add back....Sooner or later you will hear the hum and you will know the source.

Hope that helps a bit.
vegasears
1,173 posts
 
Post the question over in Audio Asylum. Luke Manley, the owner of VTL answers thread all the time over there. The amps specifications state EL-34 and you are using KT-77's. Is this a resent change?
good luck
lake513 OP
123 posts
 
Vegasears ; Last year I had been told that a KT77 was a replacement that would work and it does and I think it sounds very nice. You are right the VTL amps are designed for a EL34 or 6CA7 tube. The KT77 may be pushed a bit in the VTL amps as I was told today by a designer of very high end triode amps. They can work just great but some minor circuit changes may be needed to get the most from a KT77. I have determined that the noise in the amps is in the input stage of the amps the output stage is very quiet . I now need to figure out what to do and how to fix the problem . I will be talking with Larry Moore of Ultra Fi the previous mentioned designer about how to proceed with a fix . I may also look in to getting the amps to work there best with a KT77 tube. Thanks for the ideas everybody this is what makes Audiogon great. Marc
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