B&K ST-140 power amplifier Sam Tellig 1988
In discussing the Revelation Basic preamplifier, I pointed out that one reason it sounded so good was that Superphon's Stan Warren could ill afford to put in any more parts. (Along with Alvin Gold, I believe that the simpler, the better. This is why the Epos ES-14 speakers are so good: there's hardly any crossover. And why the B&K ST-140 is such a nifty power amp: there's mostly space inside the case.)
B&K has now introduced a mono version of the ST-140, which puts out 150Wpc into 8 ohms with 28 amps peak-to-peak current. The stereo version puts out 105Wpc into 8 ohms with 14 amps peak-to-peak current. The ST-140 mono ($996/pair) is thus more capable into low-impedance and otherwise difficult loads. It can deal successfully with such speakers as Apogee Calipers, Magnepan MGIIIs, Acoustat 2+2s, MartinLogan CLSes, and Wilson WATTs.
What's there to say about the ST-140 mono that hasn't already been said about the ST-140 stereo version? Not a whole lot—which is good news indeed. All the sound qualities that have made the ST-140 such a popular amplifier have been preserved—with more power and more current.
All the flaws of the ST-140 are preserved, too. There is no gain in overall transparency. The ST-140, mono or stereo, still sounds overripe in the bass, has a warmish coloration, softens treble transients, and is generally rolled off. The upper midrange is slightly grainy—that old MOSFET mist. None of these flaws is serious, though. The ST-140 is listenable—easy to forgive the flaws and forget, because the sound is so sweet.
Actually you do gain something, sonically, with the mono amps, besides the watts and the amps, the jolt and the juice. You gain separation, stage width, and imaging ability. What's more, the soundstage stays deep, wide, and stable, even in loud passages. There's a definite improvement over the stereo version, even if you use the amps on a load that could easily get by with a single ST-140. Whether it's worth paying twice the price, of course, is your decision.
If you already own an ST-140 and find that it's not adequate, you can have your amp updated and adapted to mono, and then purchase an additional mono amp—your dealer can provide details, which have to be worked out with B&K and which would depend in part on the age of the amp (ie, how many parts have to be changed).
And if you're thinking about an ST-140, you can always buy a stereo version and leave open the possibility of going mono.
It would be better still if the amps were instantly user-bridgeable to mono, the way the Rotel amplifiers are, but still this is a flexibility you don't always have with amplifiers: the ability to upgrade without selling your stereo ST-140. And B&K is very accommodating.
Our regular Thursday-night listening panel compared the B&K ST-140 monos with a pair of Rowland Model 7s—$9800/pair, or ten times the money. As you might expect, the Rowlands won! It was instantly apparent that the Rowlands were clearer, cleaner, and much more extended on top. There was more detail, and imaging was more precise. (The Rowlands were running in the balanced mode with the Coherence One preamp.)
But the B&Ks did not fall on their faces. They drove the WATTs with no sign of distress—no mean achievement. They always sounded sweet and smooth, with nary a trace of hardness or strain. And the soundstaging, while not as precise as the Rowlands', always held up.
As one listener said of the B&Ks and the Rowlands, "These amps are cousins. For all the differences, there are similarities in the sound." Yes, and if you like the Rowlands but can't afford them, then you will like the B&Ks and probably can afford them. Very highly recommended, and, in my opinion, a lot better value with a pair costing just $100 more than a single Superphon DM220. I should also mention that the B&K ST-140 has an excellent reputation for reliability—this from a dealer who's sold more than 500 of them!
The B&K Mono ST-140s need to be broken in. They did not sound good for the first 48 hours—dark, muddy, grundgy, and very grainy. After a couple of days, the sound became much more transparent. For best sound, they should be left on all the time. But if you don't, once broken in, they start to sound good after about a half hour to an hour. The amps run exceptionally cool. And quiet. I also find the appearance very handsome.—Sam Tellig