Problems with Unbalanced to Balanced line matching transformer from EDCOR

[sugarn]

I have tested input/phase splitter transformer for unbalanced to balanced line.
I use CD player with XLR and RCA output so that I can easily compare RCA and XLR connections.
My pre. amp. is tube pre.amp. / XLR input.
Schematic from here.
Chapter 4
Figure 18
No LL1674 as input transformer but I’ll use S2S10K/10Kt from EDCOR instead in this testing.
S2S10K/10Kt is a stereo unbalanced to balanced line matching transformer in plastic separate box.
EDCOR Electronics Corporation. S2S10K/10Kt
My testing :
1. CD player XLR -> Pre. Amp. XLR - XLR cable connect , no S2S10K/10Kt - Works fine , no hum , very quiet
2. CD player RCA unbalanced -> S2S10K/10Kt -> Pre. Amp. XLR - There is music sound but a lot of low frequency hum , hum is louder than music.
I recheck all wire connections and I’m sure there is nothing wrong with it.
My assumptions :
1. Since testing no.1 has no noise, no hum so this proves there is no any ground loop problem in my system.
2. Testing no. 2 has hum problem when putting S2S10K/10Kt in so the problem must be related to S2S10K/10Kt.

I have contacted EDCOR by email. With several contact emails he advised me to put a wire across S2S10K/10Kt like this.
From testing no. 2 above , add a wire from CD player XLR ground (pin 1) to pre. Amp. ground.
Result from this testing : There is no hum , the hum is gone , sounds good.
I email EDCOR telling about this result. EDCOR respond there is no problem with their product and accused on the ground loop problem. But my system already works fine , no ground loop problem when there is no S2S10K/10Kt in testing no. 1.
I think S2S10K/10Kt is the problem.
Maybe ground/center tab of S2S10K/10Kt’s output is wrong because adding a wire from CD player XLR ground (pin 1) to pre. Amp. ground has eliminated hum.
Maybe there is impedance mismatch, 10K source to 10K output?
I welcome opinions and suggestions here.

[David Davenport]

Hello,

You might find an answer to your problem in my article on grounding and interconnection here:

http://www.raleighaudio.com/Audio%20...connection.pdf

Dave