Ground loop and P10

The system starts with a P10. All electronics are plugged into the P10. The P10 is plugged into a dedicated 15 amp breaker. In the elimination process should I start with the P10 out of the system? I thought I understood the ground loop trouble shooting process, but when the hum was still present with shorting plugs in the input jacks of the phono preamp, it seemed like I had found the culprit. Now it is difficult to know where to start.

System is as follows: P10; cj: ET5 line preamp, TEA2MAX phono preamp, ARTsa amp; VPI Prime (Phoenix Engineering Eagle PSU - not plugged into P10); Technics SL1200GAE - plugged into P10); Sony: HAP-Z1ES Audio Player, XA777ES SACD; McIntosh MR78 tuner. All cables including interconnects and power chords are Audio Sensibility Statement Series.

Thanks in advance for any help you can provide.


Start here:

If you follow this process strictly, you’ll come up with the culprit. Works every time if you actually follow it. Once you uncover which product it is, then let us know and we’ll help you figure out what to do about it.

The phono preamp is enroute from cj. When it arrives I will follow your procedure and get back to you with the result. Thanks. BTW, I particularly enjoyed the discussion in the last edition of Copper in response to Ethan Winer’s article.

Yes, it was a good discussion. Got to see all sides when we can.


This note is sent in followup. I followed your ground loop discovery procedure to the letter. The culprit still came out to be the phono preamp. An interesting discovery was found at cj’s suggestion. They suggested plugging the P10 into it’s own power outlet with no other component(s) using the same circuit. Originally I had also plugged in the Phoenix Engineering Eagle PSU together with the P10. All other components into the P10 and a VPI turntable into the Eagle. Unplugging the Eagle and powering it from a different outlet in a separate circuit cut the hum level by perhaps 30% or more. I found this to be counter intuitive, but there it is. The Eagle works in conjunction with their Roadrunner tachometer which has a feedback loop to automatically correct any deviation from the set rpm of the platter. There must be some sort of weird interference going on.

Anyway, back to the phono stage. It has a gain of 55 db and my best cartridge only has an output voltage of 0.3 mV. Couple that with tubes, even new tubes, and there is the source of the hum. I bought a 5:1 step up transformer from Bob’s Devices (~15 db) and the problem was instantly resolved. Thanks for your help.