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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
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.
last_lemming OP
639 posts
 
Ok. I tried all Components from the same outlet to no avail. Still got the hum. 
However i think I’ve determined it’s tied to the cartridge - I think. 
It’s a brand new Grado Sonata 3 - Timbre series. Couple things - I know Grado’s are known for their “hum”, but in this case I get hum when there is no record playing and the motor is off and the tone arm is at rest - rest of the system is on. If I unplug the IC from the TT to the phono pre the hum stops.

there is no change in hum when the record is playing, needle up or needle down, close or further away from the spindle. 
I’ve also moved the TT around and away from the phono pre to no avail.  I was only able to move the TT about 2 feet away from phono pre, amp, and preamp, so I’m not sure that’s far enough. 
i tried laying tin foil over the cart to see if it would shield it, but it did not. Though I’m not sure that’s an effective way to test. 
This cart’s output is 1mv where my previous was 2.5mv, so I don’t really know if it’s this cart specifically or the all carts since I have to turn it up much louder to get to the same dB level. But my gut says it did.  

Not sure if there is a “fix” for this, but I REALLY like this cart so I’d hate to send it back. It only hum audibly at a bit over halfway up, which men’s i only really her it in the quite sections. 
br3098
996 posts
 
This sounds like a ground potential issue. Try running a ground strap from the phono pre to your preamp. I know you tried what millercarbon suggested but sometimes you need to isolate two plugs in the same receptacle. I have had good luck using a simple surge protector like these: Tripp Lite ISOBAR6Ultra Power Strip
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