Recommend Class a Amp

Good call by Czarivey and Bombaywalla. I dug out the original Stereophile issue to see if there was a manufacturer's comment in response to what JA had to say, and there was not.

To the OP: If I were you I would forget about pure class A operation and jump on this refurbished Threshold S/500 Series II, being offered by a dealer at $2495. I note, though, that in addition to being listed at the dealer's site he is offering it with a "buy it now" option at a well known auction site, so it could be spoken for at any time.

I have no affiliation with or knowledge of the seller.

Regards,
-- Al

03-28-15: Abrew19
If you value bass quality, ignore what Tjassoc wrote above regarding the low wattage Pass full class A amps. While I haven't owned the xa30.5 I do own the older Aleph 5 which is a 60wpc full class A model. AND I also own the newer x250.5 which is the 250wpc class A/B behemoth. So I do direct comparisons frequently. While the full class A Aleph delivers absolutely delicious mids and high frequencies, the bass quality isn't great.

I would not extrapolate any conclusions about the bass quality or any other aspect of the sonics of the XA30.5 from experience with the Aleph 5. They are completely different designs, starting with the fact that the XA30.5 is a fully balanced design while the Aleph 5 is not only not balanced but is not even push-pull, being single-ended.

That said, I am not asserting that the XA30.5 would be a suitable match for the QLS-1. I couldn't find efficiency or sensitivity specs for the QLS-1 (although I note that it is recommended for use with amplifiers rated from 100 to 500 watts), but I suspect that its efficiency and sensitivity are much lower than those of the Wilsons Tjassoc referred to, as well as its impedance characteristics being difficult. FWIW my guess is that the XA30.5 would often be struggling to some degree when driving the QLS-1, especially with recordings having loud orchestral peaks or other instances of wide dynamic range. I say that despite Stereophile's measurements indicating that the XA30.5 can provide 195 watts into 4 ohms (more than twice as much as the Aleph 5, btw), although not in class A above about 60 watts.

Regards,
-- Al

Wow! Congratulations, John. I seem to recall that you were thinking of the Ulysses a while back. Hope you are enjoying them as much as I do mine!

And re the INT-30A, I **would** expect your experience with it to be likely to have relevance to the XA30.5, in contrast to what I said about the Aleph 5.

Best regards,
-- Al