Phono preamp hum


I have a inexpensive Bellari phonostage that sounds pretty good after a 15 minute warmup, but develops a terrific hum after about 30 minutes.  It has one tube.  Anyone have an idea?

boxcarman

I have no idea if it has an AC filiment supply.  It has a wall wart power supply.  Once it starts humming, it gradually gets  louder and I have to unplug it to stop.

Have you checked the grounding? Make sure the ground wire is tightly secured. Then try removing the ground wire. Is your linestage plugged into the same outlet as the Bellari? If not, make it so.

Yes, the ground wire is secure.  I have tried grounding it a few different ways with the same result.  Like I said, it sounds fine for about 30 minutes, then the humming gradually becomes louder the longer it plays, or even not playing.

It’s impossible to solve this sort of problem “long distance”, once you’ve eliminated the obvious. You did not answer the other obvious question; is your phono stage wall wart plugged into the same outlet as your linestage and amplifier? If not, try that. If yes, then maybe consult Bellari in Colorado.