Solid State Power Amp Reviews

Guy Lemcoe reviewed the B&K ST-140 in December 1989 (Vol.12 No.12):

This $498 amplifier (footnote 1) has been around for quite a while, the first review—by the one and only JGH—occurring over five years ago. He liked it, as did Sam Tellig, the Audio Cheapskate/Anarchist (Vol.7 No.4, Vol.8 No.8, Vol.10 No.7, Vol.12 No.4). It incorporates class-A pre-driver circuitry driving a class-AB output stage (this using, unusually in view of the specified power, just one pair of complementary MOSFETs per channel). A large toroidal transformer coupled with 34,000µF of capacitance serves as the power supply. Current capacity is quoted as 14A peak-peak. Other features gleaned from the rather sketchy spec sheet indicate gold-plated input and output connectors and the use of 1% metal-film resistors in the entire active circuitry. The review sample was of recent manufacture.

The amp is unassuming in appearance and, I feel, very attractive. Unlike the other amps in this survey, the ST-140 does not exude a "macho" image. Instead, it understates its functionality through conservative styling. A rocker switch on the front panel turns the unit on and indicates power by lighting up. A pair of rather delicate-looking brushed aluminum handles completes the picture. Heavy-duty 5-way binding posts grace the back of the amp, along with a pair of the most inconveniently located input jacks I have come across—under the heatsink! When I turned the unit on I was not greeted with any surprise pops; likewise when I turned the amp off. Excellent!

Also excellent was the incredible amount of detail presented by this amp. The ST-140 was the champ in retrieving low-level detail, but this ability came at some cost. LP surface noise was excessive through this amp. It was hard not to focus attention on it, at the expense of the music. Perhaps there is a slight bump in the frequency response to explain this characteristic. (Bob Harley, our technical editor, will get this amp on the bench to see.) The Tom Waits cuts came across brighter than on either the PS Audio or the Adcom. The intimate ambience of the recording was captured well, as was the unique timbre of the glass harmonica. The bass did not appear as "full" as on several of the other amps. The extension was there, but the body of the instrument seemed missing or underscaled.

The Romeros' LP sounded okay with this amp, though the guitars sounded leaner. There was loads of fine detail, especially the very prominent finger noises of the soloists. In fact, the pattering of the fingertips on the strings became a counterpoint to the actual music, a strange and interesting phenomenon. On The Trinity Session, the "air" of the church on cut 1 was not as palpable as on the Adcom GFA-555 or PS Audio. Stage depth was good, but not as deep as on the Adcom. Lots of detail was evident here. Margo Timmins's voice seemed lighter, with harsher sibilants. The bass was weaker in both volume and body. On James Tyler's record, the ST-140 again took the lead in resolution of fine detail. The usual performer noises were there, as were sounds external to the hall. Traffic noise was clearly audible, as was the barking of a dog. Inside the hall, the chirping of several birds was clearly heard just after the dog bark. The B&K rendered these sounds clearer than any of the other amps. Timbre of the early instruments sounded a little lean, with a bit too much sinewy quality on the strings. Focus on the instruments was good, with a natural rendering of the soundstage; perspective was a bit more forward than the Adcom or PS Audio, though.

The soundstage on The Wellpark Suite was excellent, with good depth. The "sound" of the studio was easily heard, especially during the energetic drum solos. These moments also demonstrated the speed of this amp in handling transients. Excellent! Bass was a little weak in comparison to the Adcom and PS Audio, but was fully extended. Toward the end of the piece, I sensed a bit of congestion as the music became more complex and dynamic. Perhaps this amp was just beginning to run out of steam.

On Poem, the sense of the auditorium was not as obvious as on the other amps in this survey. The flute also lost its burnished-metal sound here (as if a polishing cloth had been taken to it), and, overall, sounded lighter in tone. The bass register of the piano also took on a lightweight character. I did not get the sense that the piano was anchored to the floor of the stage. The climaxes in the music seemed strained, with the flute taking on a harsh sound and the piano turning brittle. I was disappointed in the way the B&K handled this recording. I have heard much better.

Conclusions
The months I spent with these amps made me much more aware of the kind of sonic signature I can tolerate in a component. What had started out as an exciting assignment turned out, after several weeks of listening, to become tedious and quite fatiguing, both mentally and physically. I found myself getting into a rut. There were times I didn't even want to turn on the system. I was coming dangerously close to audio burnout. But that stage of the review process passed, and I returned to my work with a stronger desire to finish what I had been asked to start. I hope our readers will be among the beneficiaries of my research. I know the local electric company was!

Overall, I was impressed at how fine these amps sounded. Each had its vagaries, some of which I accepted more than others. The B&K reminded me of the classic solid-state amps of earlier days. It had a lean, highly detailed sound which on first hearing was exciting, but eventually, for me, became fatiguing. The midrange sounded as if it had been sucked out of the music. The B&K drove both electrostatic amd dynamic speakers with nary a complaint, conveying the dynamics of the music adequately but leaving me in the cold when it came to my becoming involved with the performances. I felt like an outsider looking in on a musical event through a screen.

For someone who owns speakers with limited high-frequency response, the B&K might serve well. They might also match up in a system which includes a cartridge with a rolled-off high end. Detail freaks will love this amp. I love detail but could not warm up to it. For those on a tight budget, however, I still recommend the B&K ST-140 with the caveat that other components in the system be chosen with care. Choose a front end and speakers which will not accentuate the ST-140's somewhat cold sonic signature.—Guy Lemcoe

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Footnote 1: Notice how price inflation has gripped the audio business? Five years ago, according to the October 1984 Audio directory, the Quicksilver power amps sold for $995/pair. Now, in a slightly revised version with KT88 output tubes, the uncaged Quickies sell for $1850/pair. Almost double the price. In October 1984, the cheapest Threshold amp was the 90Wpc S/150, with a list price of $1490. Today, the least expensive Threshold is the 50Wpc SA/3 for $3150.

Yet some manufacturers have managed to hold the line on prices. Adcom, for instance. And B&K. In 1984, the ST-140, then a 70Wpc amp, retailed for $399. In 1989, the ST-140, now a 100Wpc amp, retails for $499. That's a 25% hike over the course of five years. Not bad. What is it about containing costs that B&K knows and other manufacturers don't?—Sam Tellig