It's an exciting time here at Jeff's Place, as the Pass Labs XA25 power amplifier has just arrived for review at Positive Feedback.
I'm quite delighted that I am able to write about the Pass Labs XA25 power amplifier for you here at Jeff's Place and Positive Feedback, as they are difficult to come by, and they have been selling out as soon as a new batch is made due to their desirable combination of high-performance and a relatively affordable price of $4900 USD.
Let me share the owner's manual introduction of the Pass Labs XA25 with you for a little background on the amp.
"Entering their 22nd year of production, the X and XA power amplifiers have remained at the cutting edge of audio through continuous innovation and refinement. At Pass we build amplifiers with excessive output stages, huge heat sinks and massive power supplies. We use the highest quality components in simple linear topologies, assembled and tested with great care in Auburn, California. The measure well and sound great. They are heavy, reliable and expensive.
The new XA25 offers this at slightly lower power, without frills, at a lower price. It embodies new components and innovative circuits coupled with the best elements of the previous generation.
The signal path from input to output has been simplified to fewer components. Degeneration, “the other form of feedback” has been eliminated. The output stage consists of a single pair of 800 watt new generation output transistors operating push-pull Class A. We still use the same “New Old Stock” of small power JFETs and cascaded MOSFET, in the classic “CFA” voltage gain circuit. The amplifier is still DC coupled and has no frequency compensation.
The result is faster, lower distortion, lower noise, higher damping and larger Class A operating envelope into low impedance loudspeakers, all in a simple 3 stage circuit with total of three pair of push-pull gain transistors.
In their ideal state, matched push-pull FETs give perfect “square law” cancellation of distortion, an effect somewhat spoiled by degenerative Source resistance used to constrain the “personality” of the devices. The removal of this form of feedback is an important element in the performance of the XA25 and is accomplished by new approaches to stabilizing gain and bias of push-pull FETs.
This gives a lower output impedance, more gain, and lower spectral content of distortion, as evidenced by measurements (see the specs section), but the more important factor is the difference it makes to the music.
We observed this difference some years ago in listening tests. Degeneration removed some of the organic quality to the sound and so became the subject of further development work.
The XA25 measures superbly, but it’s subjective qualities are most special. In an industry where products with great specs are frequently found to be dry and boring, this amplifier breathes life into the music."
I still have the First Watt SIT-3 power amplifier (review HERE), which will make for interesting comparisons to the Pass Labs XA25 power amplifier.
As you know from my review of the SIT-3, I thought it was incredibly good, being the equal or better of any solid-state or tube amplifier I've ever heard, but its 18 watts of output power meant that it needed to be paired with more sensitive loudspeakers. Behind the scenes, some of the reviewers at other audio periodicals have said they thought it was possibly the finest sounding amplifier ever built, regardless of price, and it is indeed very, very, good.
Enter the Pass Labs XA25 whose 25 watts of output power allows it to drive even less sensitive loudspeakers, as well as difficult loads down to 2 Ohms.
I'm looking forward to trying the Pass Labs XA25 on my Tannoy Westminster Royal SE loudspeakers (8 Ohms) that the First Watt SIT-3 sounded so incredible on, as well as on the Duelund-Altec Project vintage Stokowski Altec's with their new state-of-art Duelund CAST tinned-copper crossovers (16 Ohms).
Stokowski Altec's with their Duelund CAST Sn-Cu crossovers.
I have a couple of reviews I'm working on now (i.e. the Hanze HiFi HAT turntable power supply and the Duelund-Altec Project) that I have to get done before I can write up the review of the Pass Labs XA25 for Positive Feedback, but you can expect me to write about my preliminary impressions of it here at Jeff's Place until then.
Stay tuned, their will be much more to come on the Pass Labs XA25 power amplifier, and as always, thanks for stopping by, and may the tone be with you!
