Disappointment with Pass Labs - I'm looking for something else

@hifi59 ugh… zombie thread. Most Pass amp amps “don’t measure well” they aren’t designed to “measure well”. They are designed to sound good. Read Nelson’s take on this on the website.

@hifi59  That´s the first time I've ever seen a Pass amplifier measure at less than specified power.  On multiple other occasions reviewers have explicitly noted that the amps are very conservatively rated.  

See, e.g., this stereophile review of the XA30.5: 

"Fig.4 shows how the THD+noise percentage in the amplifier's output varies with output power into 8, 4, and 2 ohms. While the XA30.5 may give 30Wpc into 8 ohms in class-A (14.8dBW), the distortion at this power level is low, at 0.015%. The amplifier doesn't actually clip (defined as the THD reaching 1%) until a much higher power level: 130Wpc into 8 ohms (21.14dBW). Even higher powers were available into lower impedances before clipping: 195Wpc into 4 ohms with both channels driven (19.9dBW), and 332W into 2 ohms with one channel driven (19.2dBW)."

And another for the XA25:

"The INT-25's output power is specified as 25W into 8 ohms and 50W into 4 ohms, both equivalent to 14dBW, with a "class-A envelope" of 50W peak into 2, 4, or 8 ohm loads. With "clipping" defined as when the THD+noise reaches 1%, I found that the Pass Labs amplifier with both channels driven at 1kHz clipped at 60W into 8 ohms (17.8dBW, fig.4) and 98W into 4 ohms (16.9dBW, fig.5)."

I think the X350.5 was actually broken.  As he notes, obviously the DC offset needs to be re-biased, and given that power behavior, I think it's in need of more substantial service.   

I can understand the Pass amp distortion being higher since lowest distortion doesn’t always correlate to sounding better. It’s the fact that it couldn’t deliver close to its rated 4 ohm output. I see no excuse for that unless the amp had some unforeseen issues. Audioholics has excellent measuring equipment and I trust Gene, along with his measurements, especially when he goes to listen and it reflects what he measured.

Change the Tubes ?

Find someone in your local audio society and bring your preamp and amp over to try again with different speakers and cables. Listen closely.

Then, try it with a different preamp, lots of threads out there on this topic; xp12 vs 22 vs 30.  Borrow a really good tube preamp and be amazed.