2. analog
  3. 159523-46

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
rms456
41 posts
 
Consider induction from cables in the wall or worst case induction from motors through the platter.
jacahn
28 posts
 
Check the wires connecting the cartridge to the tonearm. Sometimes separating them more/moving them apart slightly can get rid of the hum.  Do this carefully, for example with a toothpick instead of a finger, so you don't break a connection on one of the leads.  Also, check that the phono cables (from the phono to the pre-amp) are not too close to a power cord.
last_lemming OP
632 posts
 
I can run all the electronics through a 1000w isolation transformer and I can lift the ground to the transformer and I still get the hum with no noticeable hum reduction.  I thought isolation transformers were supposed to eliminate ground issues. 

However, I ran a 50’ power cord from across the house to another outlet and it reduced the hum at least 50%. So it appears the house electricity is causing the issue in some  circuits. 
mijostyn's avatar
mijostyn
8,248 posts
 
Not sure that means anything Last_lemming. If it is the vicinity the turntable is in the only way to determine that is to move the turntable, what a PITA. The Grado is notoriously sensitive to external fields maybe if you explained your misery to a local shop and promised to buy a new cartridge from them they would let you take a demo unit home to see if that fixes it. Yes, it could be the kitchen but are you going to move everything around to get off that wall?
mijostyn's avatar
mijostyn
8,248 posts
 
Also, check your tonearm negative leads for continuity. Tonearm wires have broken. 
More to discover