2. amps-preamps
  3. 134113-6544

Audible Illusions Tube Pre-Amp Hum- Help Diagnosing

Began getting a low-level hum from the pre-amp which stays at the same low volume no matter where volume pots are set.  Both channels are affected, although it seems to have begun in one channel (or maybe it had been more noticable in one channel, or maybe it was my imagination.)

Is this a tube thing, a ground thing, or some other issue?  

Would like to narrow down possibilities before tearing apart the installation and/or buying tubes or other things unnecessarily. 

Thanks in advance for any guidance.
jimbo3
newbee
4,751 posts
 
A 'tube thing' would more likely be a static like noise and it would more likely appear in one channel (at least first). I would focus on a 'ground thing' and start disconnecting your sources, one at a time an see if it goes away. If not then disconnect your amp from your preamp and see what happens. Don't forget to turn off your amp when making these connections!
jimbo3 OP
304 posts
 
Thanks, Newbee. The one thing that is throwing my thinking off is that the hum (noise?) doesn't increase in volume, which is something I would otherwise expect to happen with a ground issue(?)  The problem seemed to have begun on one channel, though, so maybe a tube issue is still a possibility?  

I hadn't thought to disconnect sources one at a time as you suggested.  Will try that first.  
newbee
4,751 posts
 
You are right re tube noise being static and ground hums being varible depending on volume setting. I was just trying to simplify. If you have them on hand, it is more simple to change out the small tubes and see what happens.
audioconnection
1,270 posts
 
Mute the unit
 If it still hums let me know
Move the outboard power supply away.
Move the unit farther away from what is under it or above it.
Try 2 new shielded cables from pre amp to Power amp
If you have Cable tv disconnect the feed from the cable box to the pre
 if it goes away you need a Transformer on the cable coax in line.
 Best JohnnyR 
More to discover