XA 30.5 or mod S/500?

I've been watching the 'Gon fruitlessly for some time to get a Threshold S/500, "late Series II w/Optical Bias" (per Jon Soderberg, this is what he needs in order to do his modification to produce a Class A one-chassis SA/1 "clone" [my word, not his]). I'm beginning to wonder if a Pass XA 30.5 might not be equivalent or better sounding; I know they're easier to find. Unless I get lucky and find an already-Soderberg-ed S/500, the cost of amp and mod might even be approaching the price of a used XA 30.5(?). Either amp will be used with a FET 9 preamp. Speakers are currently Vandersteen 2CEs, but contemplating future purchase of 3A Sigs, or Maggie 3.6s, and a REL sub. Anyone heard SA/1s AND heard XA 30.5? Thanks.
Hi Cippoliner,

I use a pair of Threshold SA-1's and Pass Labs XA 60.5's to power my MG-20's. They are both great amps, however Nelson Pass's latest XA.5 series are his best sounding amps of his long great design career.
In this case newer is much better, go with the XA-30.5. Has your FET 9 been up dated?
Thanks for replies; nope, no update.
I have a XA30.5 and a X350.5 and have had two Jon Soderberg moded Threshold amps through out the years. Sonically speaking the Moded Thresholds sound very very good however the PASS sounds significantly better. I can tell you will need more power to drive those Magnepans 3.6 than a XA30.5. My advise is you should buy a used X250.5 or X350.5 if you can. They may not be 100% Class A but they will blow the doors off the Moded Thresholds. I had a pair of heavily moded SA/1 mono blocks with the Optical Biasing and balanced and a new right out of the box X250.5 not broken in killed the The Threshold Mono Blocks and by a huge margin.
I don't think an XA 30.5 will provide enough power to let any of those speakers demonstrate what they are ultimately capable of.
"Anyone heard SA/1s AND heard XA 30.5?"

I had a pair of SA/1's in my house for a month awhile back. They are wonderful amps, even by today's standards. I have owned the 30.5 for about 2 yrs now and have no plans to sell it. I'd recommend the 30.5 unless you like to play your system REALLY loud. If that were the case, I'd recommend getting the biggest X.5 amp you can afford.

BTW, I ran the 30.5 with my Maggie 3.6's. Worked fine. Room was 18x26x10 and the needle hardly ever wiggled (meaning leaving class A). After its 30 watts of class A, you still have another 100 (almost 200 into the Maggies) of A/B.

Another reason I like his newer XA.5 design:

The standby mode keeps the caps fully charged and draw just a few watts. When you're ready for a listen, there is still the wait (45-60 mins) til they heat up to spec but they sound good while doing so.
The X.5 amps do the same thing in stand by mode. The stand by mode on all pass amps keep the caps charged and the driver input board on. When fully engaged it they simply turn on the output transistors.

I believe your Threshold preamp is not balanced.
As long as your using this preamp, you will not be using any truly balanced amp to it's full potential.
An Adcom GFP 750 would be an instant upgrade, cheap.
Like your Threshold fet 9, the Threshold S/500 Series II amplifiers are single ended. The Pass XA 30.5 is balanced, and would benefit from a true differential balanced pre.
Thanks to all for relating your experiences and advice. I'll have to digest it all in light of potential costs - the cheapest Passes I've seen on the 'Gon were already more than I HAD been thinking of spending (you can see from my system that I've not got a high-zoot kinda rig). However, I've heard so many accolades about the Pass XA.5 series that if I don't find a good price on a Threshold to send to Jon soon, I may have to bite the Eichmann and go upmarket (won't be any unit beyond the 30.5, though, due to my budget). Thanks again to all.

If you live somewhere where you can use true Class A amps,
you should try a pair of Pass Aleph 2s. These are not balanced (even though they have balanced & single ended inputs). I believe they will mate well with your current preamp.
These list used between $2500.00 & $3K. They sell when the price is close to $2500.00.
These sound very good, to me. I've had mine for 9 years.
The big advantage of the XA30.5 is the SuSy [super-symetry]circuitry that Nelson patented. Here is the url:


I don't know if the XA30.5 will drive all the speakers to volume levels acceptable to you.