Audio Aero Capitole - 6021W subminiature tube ??

I suspect that the polarity and pin set-up between the two is NOT the issue. Do a search on invert in the preamp/amp section and you will see from some pretty knowledgeable people (amp designers, etc. . .) that such an issue is not going to cause this problem.

I think you can immediately narrow down the problem to one of three causes:

1: the least likely cause is that you balanced cables are defective. Use, borrow or buy (even a cheap one at a local musical instrument store) and try the new one and see if the noise goes away.
2: there is an issue with the power amps' balanced input handling of that signal internally in the amp (this can easily be tested by an RCA to XLR plug, running the RCA from your Capitole to the balanced in of your amp to see if you are still getting the white noise).
3: there is an issue with the balanced outputs of the Capitole (you can determine this by buying or borrowing an adapter so you run the XLR balanced cable out from the Capitole into the single ended inputs on the amp and to see if you still have the white noise). I suspect this is going to be your problem. Why? Because the Capitole CD players are known for failing or breaking down. They are musically great sounding, but they are made in France!

I have done tests with multimeter, happens that I have Fluke, so I could get pretty exact measurements.

>check for continuity between xlr pin 1 and the ground sleeve of an rca connector

there is continuity 0.14ohm which is 0 for my Fluke.

AA Cap
RCA - 0,52 ohm
XLR - pin 1,2 0,45ohm
XLR - pin 1,3 0,57ohm
XLR - pin 2,3 0,83ohm

I was surprised how low output resistance of this CDP is.

Clayton
RCA - infinity
XLR - pin 1,2 0,85ohm
XLR - pin 1,3 infinity
XLR - pin 2,3 infinity

So it seems like Clayton is not a balanced amp, he is is the culprit, am I right ?

Wow! Those are indeed strange readings. Let me first verify a couple of things, which I hope you won't mind my asking:

1)Did you make these measurements with power off, which is how they should be measured? If power was on, voltages such as dc offset, ac leakage, etc., might have confused the meter.

2)When you say "0,45ohm," "0,57ohm," etc., am I correct in assuming that you mean "0.45 ohms," "0.57 ohms" etc? And are you sure that the scale the meter was set to was ohms, not Kohms?

Assuming those answers are "yes," I too am very surprised at the low readings on the cdp outputs. However, the 0.14 ohm reading from xlr pin 1 to ground appears to confirm that pin 1 is ground, as it should be.

Did you also measure from xlr pin 1 on the Clayton to its ground (the shell of an rca connector, or chassis)? Looking at your readings, I'm wondering if perhaps for some strange reason pin 3 is used as ground on its xlr connector, instead of pin 1.

Best regards,
-- Al

1) Yes I did measurements with power off.
2) Yes I meant 0.45ohm

I did some additional measurements:
Clayton:
XLR Pin 1, ground (on chassis) 0.28ohm
XLR Pin 2, ground (on chassis) 0.9ohm
XLR Pin 3, ground (on chassis) 22Mohm and falling

XLR Pin 1, RCA ground 0.18ohm
XLR Pin 2, RCA ground 0.8ohm
XLR Pin 3, RCA ground 32Mohm constant

Thank you for your interest.

OK. Perhaps the very low numbers looking into the Capitole's outputs indicate that its outputs are transformer coupled. If that is the case, dc resistance measurements probably don't tell us very much.

Based on the additional measurements, I agree with you that the Clayton's xlr inputs appear to be unbalanced. It looks like pins 1 and 2 are both grounded, and the only input used for signal is pin 3, perhaps through a capacitor.

Since the xlr interface therefore appears to be essentially an unbalanced interface, it might be worthwhile temporarily isolating the amp's ac safety ground, via a cheater plug. Perhaps a ground loop, to which unbalanced interfaces are susceptible, is causing the noise (although a ground-loop problem would usually involve low frequency hum, as well as high frequency buzz, and I'm not sure why the rca output would be quiet if a ground loop were the problem).

Also, I'm wondering if the Capitole's output circuit may be having problems due to having the signal it outputs onto pin 2 shorted to ground, by the Clayton. If possible, it might be worthwhile trying a specially prepared xlr cable that leaves pin 2 unconnected.

Just some thoughts.

Best regards,
-- Al