Small suites needing low wattage/highest transparency amps should make a pass at these pure Class A beauties.
by John Gatski, 2.15.2008
John Gatski is the Publisher & Executive Editor of Pro Audio Review.
With fewer and fewer passive speakers being offered to the pros, studios that want to power passives also have fewer pure pro-oriented studio amps from which to choose.
Nonetheless, some of the audiophile/pro amps — from manufacturers including Pass Labs, Bryston and Lipinski Sound — have long been used for driving passive speakers by a number of high-end studios. Indeed, PAR has been reviewing Pass and Bryston amps for nearly 10 years.
Now PAR turns an eye to the Nelson Pass-engineered XA30.5 amp, from the XA series.
Features
The $5,000 (gulp!) XA30.5 is a pure Class A stereo amplifier, cranking out a modest 30 watts per channel, utilizing Pass’s Super-Symmetry, tightly matched MOSFET topology with very little global feedback. This is unlike the X Series, which uses a similar topology but runs in Class A/AB.
Heavily-biased Class A amplifiers need larger power supplies, run hot and use a lot more power than comparable powered Class A-A/B or Class A/B amps. Thus, a 30-watt version is a reasonable power range to keep the unit operating in a reasonably sized package without being too hot and an energy hog. And, in my experience, Class A amps can be extremely revealing.
Fast Facts
Applications Studio, post
Key Features 30W per channel; Class A stereo; FET SuperSymetry Circuit; balanced/unbalanced inputs; front panel current meter; 12V power trigger; three-way speaker posts
Score If you have the bucks and the speakers, this amp delivers transparency and musicality the way it is intended.
Typical of Pass amps, the heavy duty XA30.5 is classy looking with its silver front panel, blue back lit current meter and large power toggle switch. In my opinion, if a component is expensive, then it should look it.
The rear of the amp sports three-way speaker binding posts, XLR and single-ended RCA inputs, and a 12-volt trigger input for remote turn on. The large, angled heat sinks take up the left and right sides. The unit weighs about 60 pounds.
Factory-claimed specs: 30 watts continuous into 8 ohms (60 watts at 4 ohms), 1.5Hz - 100kHz frequency response -1dB, -2dB; and under .1-percent distortion at rated power. Dampening factor is 150 ref to 8 ohms nominal, and the slew rates is +, -50V/uS.
In Use
I used the XA30.5 in two configurations: driving Legacy Focus 20/20s far-field monitors and powering a set of Westlake LC 8.1s, a pair of Lipinski L-505s and a pair of Generation 1 Legacy Studio closefields.
Sources in setup 1 included the Esoteric DV-50 universal DVD-A/CD/SACD player, Alesis Masterlink connected to either a Benchmark DAC1 or Lavry DA10 converter, and a Trident 8T 16-channel analog console. Sources in setup 2 included a Macintosh G5 workstation with Lynx L22 PCI card/DAC, Lavry DA10, Benchmark DAC1 and TASCAM DVRA1000.
Speaker cables were either Kimber Cable (stranded) or Alpha-Core (solid conductor), and interconnects were Westlake, Kimber Cable and Alpha Core. Power to both systems came from an Alpha Core balanced power unit, and Shunyta AC distribution box.
Other amps on hand for subjective comparison included a Pass X350.5 (350 watts per channel), Bryston 14B SST Class A/B at 600 watts per channel and a more conventional Parasound Class AB circuit amp.
On the big Legacys, I played a number of personal guitar demo DVD-As, as well as high-quality recording mixes from several engineers. It was also interesting to run the different sources through the system to ascertain their levels of transparency.
As typical with Pass amps, the XA30.5 was extremely transparent and had the widest sound stage I had ever heard with my guitar and piano stereo recordings; you could hear fine detail and the edges of transient sounds much deeper into the mix than most pro amps I had used with the same speakers. Even against the Pass X350.5, which is about as good as I had heard, there was a bit more inner detail in the image.
Now, for powerful, loud symphonic monitoring with lots of dynamic low end the 350+ watt big Pass was a better choice than the 30 watter; the little brother, however, still had pretty clean and deep bass within its power rating. Also, no matter what I put through the Pass XA30.5 it was never hard sounding; the high-midrange/low treble was as smooth as the real thing.
On setup 2 with the Lipinski and Legacy closefields, the Pass was a perfect amp to power an accurate set of high-end compact monitors. The highly accurate Lipinski’s really shined with the XA30.5, showcasing 24-bit/96-kHz stereo recordings of a custom Martin OO-28.
I found that the Pass X and XA Series to be such revealing amps that good-to-excellent passive speakers (getting harder to find on the pro side) relayed more subtleties than with typical amps. The $3,000 grand Parasound was good, but I noticed considerable shrinkage of the stereo image depth of multitrack mixed-down recordings in comparison to the Pass’.
Summary
Though pricey when compared to plethora of powered speaker models available to today’s studios, the Pass Labs XA30.5 is an ideal amp for those small mastering or tracking suites that want accuracy out of passive closefields.
I know many engineers who still swear by passive speakers. It’s for those pros (and, of course, the audiophiles) that the Pass is intended. In high-resolution playback, you can hear layers of sonic subtleties that other amps don’t come close to equaling, and there is not a hint of harshness or fatigue even at higher volume levels.
If you need more power for larger speakers in bigger rooms, and you want to stay all Class A, then you probably would want the Pass XA 100.5 model or the bigger Pass Class A/AB X.5 amps (I won’t tell you the price). But for the smaller rooms the 30 watter is plenty. You would be surprised to see how little power it takes to drive an efficient speaker.
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