I have used the Colibri XPP a few years back with the Pass Xono phono, and settled on 200 Ohm loading. Since that was quite a while ago, I couldnt remember whether I tried it with 47K Ohm though!
I've check a resistance of 9.6 Ohm (R) & 9.8 Ohm (L) on my XPP with my Protek 505 digital multimeter.
I'm using the input tap of EAR MC4 step-up that is recommended for 12 Ohm Nominal Input Impedance. This tap has a Natural Impedance of 145.1 Ohm and gives a gain of 25.1 db that elevates the 0.22mV of the XPP up to 3.96mV (x 18 times).
Also I've made some comparisons using the MC4's input tap that is recommended for 6 Ohm Nominal Input Impedance. This tap has a Natural Impedance of 81.6 Ohm and gives a gain of 27.6 db that brings to the output 5.28mV (x 24 times).
I have the (old) 6000 standard XPP model of 0.22mV output There is the (new) 8000 Platinum model with FOUR LAYER windings of 0.38mV output. But this one is offered with Titanium or Blackwood body.
Maybe the 500 Ohm it is a case of misunderstanding by VDH himself. Α mistake in translation is not very unusual. Perhaps he means the Optimum load impedance as he is probably referring inside your XPP box. (Οn my box recommends 200 Ohm).
I agree with Geoch. I dont think the internal resistance of the Colibri XPP can be any where near 500 Ohm. While the resistance of platinum maybe a little higher than copper, it cant be that much higher.
I had, and still have, the 0.22mv version of the XPP, and come to think about it, I believe the 200ohm loading I was using was recommend by VDH, by the hand writing in the box.
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