Pre-amp suggestions for Thiel 2.4/Pass Labs XA30.5

The Pass is marketed as a 30 watt Class A amp. However, it outputs 150 watts into 8 ohms and 300 watts into 4 ohms in class B. So the XA-30.5 could be labelled a 150 watt into 8 ohm Class A/B amplifier with a very high Class A bias. Read the Stereophile review of this amp if you are still not sure about this. Also consider that Nelson Pass rates his amps conservatively.

I have made a couple of preamp suggestions. I think that you would want a c-j Premier LS17 Mk II or newer, if you go c-j.

Their CT preamps use the 6H30 tube which some people don't like as much as the 6922 which c-j returned to in their most recent ET line.

Some people do like the less tubey sounding 6H30 though. If you like detail the 6H30 might be for you, with the loss of some warmth.

I would just again suggest that you get a high gain preamp in order to make it easier for your system to acheive higher volume levels so that you eliminate any concerns about the XA-30.5's suitability for your speakers.

One more thing, the XA-30.5 has a rather low 20Kohm input impedance on its single ended inputs (30Kohm balanced) so you want to keep the output impedance of your preamp below 2 Kohms single ended and 3 Kohms balanced.

Manufacturers seem to rate output impedances as an average like speaker makers do, 8 ohm average or 4 ohm average impedance. Their speaker impedances often dip below this average though and preamp output impedances often go above the rated number. So it's best to find a review that measures output impedance of a preamp to be sure what you're getting.

Tomcy6, actually Stereophile measured 130, 195, 332 Watts into 8, 4, 2 Ohms respectively, before clipping (as defined by 1% THD). If one were to use the 2 Ohm measure and work up, it would start to look more like an 80 Watt high current Class AB amp. Since the OP speakers don't drop to 2 Ohms, I thought we could be a little more generous with a 100 Watt high current Class AB designation. All in all, still rather close to Thiel's minimum recommended power.

I had a Thiel 2.4SE which I traded up for a 3.7

I've heard it with different combinations of Pre and Power before.

For my money, I found the Bel Canto Pre3 and REF500M to be a good pairing. I found the Bel Canto

If the budget could stretch further, I'd use a tube preamp which adds lushness and some 3dimensionality. I've heard it partner well with LAMM preamps and also with my Audio Research Ref5 and now 5SE. I am not a fan of overly warm and slow music reproduction and like dynamics so these two have been a great combination for me when I use SS power amps.

Unsound, I stand corrected.