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Getting him in my ARC PH3se phono pre

I use two isolation transformer to hook up all my equipment. 
One has the phono pre, TT motor (VPI Prime) and the speed controller equipment for the TT - 250w.  The other has the preamp, and amp - 1000w. 
I’m getting a hum when I turn up the volume when listing to audio through the TT. Here are the are the conditions it’s happening under:

1. Phono pre must be on for hum to occur. If turned off hum goes away. Obviously, so must amp and preamp Be turned at the same time to hear the hum. 2. Phono pre on, but TT motor off, hum is present. So no music playing. Btw motor is controlled by Eagle and Roadrunner. 3. Phono tubes are new and in good condition. 4. The Phono unit is an older unit, but when I had it connected to another system in another room I did not have a hum problem. 
Not sure where to go from here. Especially since I’m connected to isolation transformers. 
last_lemming

Showing 1 response by millercarbon

millercarbon's avatar
millercarbon
12,531 posts
 
Move the phono pre over to the same outlet as the pre and power amps. Or move the pre amp over to the same outlet as the phono stage. Either way will eliminate your ground loop hum.

If you're short on outlets you can move the motor or controller. Those probably won't matter as they are outside the signal path. The phono stage however is grounded to the pre-amp and so needs to be powered from the same outlet as the pre-amp in order to avoid potential ground differentials, which is probably the cause of your ground loop hum.
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