Pass X150.5 vs. X250.5

I have owned two Pass amps. The meter at 11:00 isn't pushing the amp all that hard. So I'd be a little surprised if the harsh peaks you are hearing are attributable to the amp being overtaxed. I therefore think you should look elsewhere in the system for the source of the harshness, before you consider changing amps.

Bryon

Perhaps not. There is not much more class A headroom between those 2 models. You would be going from 10 watts to 15 watts into 8 ohms. You'd probably need to go to the XA60.5 to get an improvement, but it depends upon the size of your room. With a big room, you may even need to get the XA100.5, or a more efficient speaker.

Kind of figured there was not much to be had by going to the 250.5. The speakers are average efficiency, around 6 ohm if I remember correctly. The room is roughly 13x18x8, so about average too. Ww carpet on floor, some absorbers at first reflection, no real furniture to speak of other than 2 cabinets on side walls. Using Pass X2.5 pre, all balanced Acoustic Zen Matrix Reference, Kimber 12TC double bi-wire to speakers. Playing with speaker position and tilt forever! Guess that is the direction to go for now!

I owned the 150.5 in the past and have spent a fair amount of time listening to their amps. I currently own an Aleph for a specific pair of speakers in which it matches well (60/90 watts 8/4 ohm, all class A). IMO, buying a/any Pass Labs amp should be based on your anticipated amount of required power being able to be driven by said amp when it is still functioning in Class A.

My experience with the Pass Labs amps is that their performance when it moves from Class A to A/B changes notably. In AB they are decent amps (not great amps) and become strident in class A/B versus their characteristic sound in pure class A.

As the poster above stated, going from the 150.5 to the 250.5, while delivering more total power, its added power in Class A that is important. In this sense, it is not a big increase (if you look outside of just the percentage increase - 10 to 15 is a 50% increase - but still not much in class A).