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

If you're staying in Class A 90% of the time you are OK. Leaving Class A is not going to cause any harm. At 4 ohms you still have 240 watts of Class A/B headroom left when you leave Class A.

Some people feel that you need amps with a lot more power than what is required by your speakers to get the best sound. Others don't. If it sounds good to you, that's the main thing.

You can also get a preamp with higher gain so that you get more volume out of your system. c-j and Aesthetix preamps have gain in the 26 db range which is considered high, I believe, if you're interested in tubes. I don't think either has a phono preamp though.

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.

Unsound, I stand corrected.