Preamp for Pass

Just to provide a contrasting opinion, I demoed my Pass XA200.5 with the Joule LA300ME and it was a poor match in my opinion. The midrange was interesting for the first several hours, but then I found it cloying and boring. Plus, I lost the treble and bass extension, the dynamics, and clarity/transparency that I get with the BAT Rex. While I still wonder about the truly balanced and much greater power Joule LA450, the sound and build of the 300 definitely reduced my enthusiasm to pursue the next step up the line.

My opinion is that the BAT Rex is a winner with the Pass XA.5. I cannot speak to the VK52 or VK51 since I have no direct experience. I've read others who were disappointed by the Audio Research/Pass pairing, but never personally pursued the ARC Ref preamp line. Good luck.

The input impedance of the Pass can be challenging for many tube preamps, including the ARC, which was covered in another thread.

This usually has to do with the output coupling capacitor of the preamp. A few tube preamps (a very few) are direct-coupled and so don't have this issue. At least one not only has direct-coupled outputs but is also fully differential and balanced. So it is possible to have the smoothness and detail of tubes without giving up anything in the bass.

Which one? :)

The RCA input impedance of the XA30.5 is 20k. Pass originally listed it at 15k but it was tested at 20k and Pass has changed that spec on some of its literature.

On preamp output impedance: remember the spec is the "average". Just like an 8 ohm speaker is hardly ever 8 ohms across the spectrum (it could vary from 2 to 30 ohms). Some pres will be many times more than its rated spec especially at the low or high end. Try and find those specs when you go hunting.

Pubul57, both the Atma-Spheres and Sonic Frontiers mentioned above, have DC coupled outputs and are fully differential and balanced, with rather low output impedance's for tube products.