Pass Labs:What to expect fm XA60.5 to XA100.5

I enjoyed the XA100.5 very much until I bought a new pair of inefficient speakers and found the amps did not have quite the power the speakers needed. So I traded the amps in for a pair of XA160.5's. The result was a more open and effortless sound with a slight increase in soundstage depth and clarity. Bass also had more impact with slightly more control. There were no areas in which the sound got worse. But they are heavier and hotter, take up more space and use more energy.

Perhaps the 10.5 is the sweet spot, but if one needs more power, I'd recommend as much class A power as one can afford. There does not seem to be a sonic price as you go up the XA.5 line.

I would expect all those benefits when you move from an underpowered amp
for one with the power necessary to drive a given speaker. But I'm not sure how
you know there is no sonic price driving a speaker that can easily be driven by
an XA30.5 and then driven by the 160.5 - let's say a speaker with 94db
sensitivity - I suspect, but cannot prove it since I have not tried it, that there is
a sonic price to be paid for those extra watts, when those extra watts serve no
real world purpose in being able to drive the speaker loud and with bass
control.

In your case the sonic penalty is paid when trying to drive a speaker that needs
more power than you had with the XA100.5, and when you need more power I
would not expect a sonic price being paid by adding the higher powered amp, it
is the wattage you need to make the speaker come alive and a lack of power is a
much higher price to pay than a lessening of purity due to all the added
electronics need for higher output..

However, at any power level, I think the XA.5 series is among the best sounding
SS amps available - they are all excellent IMHO. The changes you can expect in
moving from the 60 watt version and 100 watt version will depend on the
speaker being driven,

Good point Pubul57. I've never tried my bigger XA.5 amps with more efficient speakers, so I really don't know if they sound better or worse than say the XA30.5 would. I would expect some advantage from monoblocks with the separation of each channel, but that is also just speculation on my part.

I still believe the monoblock argument about separation, though it may be an article of faith as some folks I respect on things audio don't believe this is the case with well made gear, I don't know but there certainly is very highly regarded gear in stereo configuration - and my Music Reference RM9 and CAT JL2 had pretty darn good separation:) The theory certainly makes sense, and it must be an advantage to be able to run shorter speaker cables.

Pubul57,

I too have found that smaller wattage amps will generally have a sweeter/purer sound. In decision making, I always go by my ears first then work backwards with my brain to see if there is a reason for a finding, but always ears first as they are "direct coupled" to my wallet.

This has held up even with my sub-hobby of vintage receivers. I prefer the sound of the lower watt ones to the monsters of old. What I have read (but don't know first hand) is that a lot of "music lovers" prefer the sound of the Marantz 8b to the 9's and the Mac 225 to the 275. Of course the speaker, and how loud you like it, are important factors.

I have a hunch one reason might be transistors and their non-linear characteristics. The more of them you use, the more NFB you need to get the amp to "spec" right. I personally don't like NFB.

My ears like what they hear in Pass's XA.5 series and this is from a guy who loves/has 4 SET amps. I have their 30.5 and 100.5's. Don't hear much difference beween the two. From what I've read about the design, running the Mosfets in pure class A, he can put them in their most linear range and therefore use much less feedback to correct. In his paper on the "Super Symmetry" circuit, he says he uses only a tiny bit of NFB to tweak the two circuits into balance so they cancel distortion. This may be why "his" larger amps don't lose don't lose the sweetness like other designs do. His papers on the Passlabs website are a good read.