Solid State Power Amp Reviews

LG wrote about the 4B-ST in October 1999 (Vol.22 No.10):
When audio products sound great and have staying power on the market, they become classics. Two of the components used in my review of the B&W Nautilus 805 (elsewhere in this issue) have the legs to qualify as classics, but because they've been revised and we haven't heard the new versions, they've fallen off of Stereophile's "Recommended Components" listing. While the Bryston 4B-ST power amplifier and Velodyne HGS-18 powered subwoofer performed admirably when teamed up with the B&W Nautilus 805, are they good enough to remain classics?

Bryston's class-AB2, solid-state, 4B stereo amplifier—first reviewed 21 years ago in The Audio Critic—is the company's oldest surviving production amplifier. Reviewed most recently in Stereophile in May 1992 (Vol.15 No.5, p.132) in its NRB revision, the 40-lb 4B was described as a "compact, rugged, reliable high-powered amplifier that comes with a 20-year warranty." It garnered a Class B "Recommended Components" rating for its bass "slam" and "snap," but fell short in the areas of transparency and upper-range openness.

Now available in an ST version—the letters are the initials of Bryston's current designer, Stuart Taylor—the 4B-ST has a lower power-supply impedance, 28% more energy storage, improved power transformer layout, shorter lead lengths, improved signal isolation (shielded cables are run beneath the main system board instead of as point-to-point runs on the printed circuit board), and a new distortion-lowering input buffer amplifier. A review of other Bryston ST amplifiers (Vol.19 No.10, p.271) proved just how much distortion the ST circuitry could get rid of. Bench-tester Tom Norton commented, "The THD of the Bryston is so low that I used 10 times our normal output power for this measurement to get [a distortion waveform] that was not obscured by noise."

During a four-month audition, I found that the 4B-ST's overall sonic profile had markedly improved. Yes, the 4B-ST continues to be a bass master. Whether it was driving B&W Nautilus 805s, Revel Salons, or Dynaudio Contour 3.0s, the new 4B maintained total control over the bottom half of the audio spectrum. Film soundtracks, vocalists, and jazz ensembles all benefited from this amplifier's slam, punch, and rhythmic drive. While the current-hungry Revel Salon and the Dynaudio 3.0 needed more power—favoring Bryston's 7B-ST monoblocks—to deliver their full dynamic range in my large listening room, the 4B-ST equaled the 7B-ST in midrange clarity and open highs.

The Nautilus 805, with its 88dB/W/m sensitivity, proved a great match for the Bryston 4B-ST. The amplifier delivered ample pace'n'rhythm playing songs from Emmylou Harris' band, whether the pulsating tempo on "Wheels" or the complicated backbeat drumwork and deep bass chords on "The Maker" (Spyboy, Eminent EM-25001-2). Playing Jerome Harris' arrangement of Duke Ellington's "The Mooche" (Rendezvous, Stereophile STPH013-2), the 4B-ST reproduced Steve Nelson's vibes with great transparency, Billy Drummond's rimshots with terrific transient power and slam, and Art Baron's trombone with a natural bite and "brassy blattiness." While it didn't match the 7B-ST monoblock's dynamic contrasts or soundstaging, the 4B-ST has an equally open and transparent midrange. This makes the $2397 4B-ST Bryston's best 4B yet, and definitely recommended for auditioning.

The latest incarnation of the Bryston 4B-ST remains an audio classic.—Larry Greenhill

LG wrote about the 4B-SST in April 2007 (Vol.30 No.4):
During my auditioning of the company's B100-DA integrated amplifier, I asked Bryston to send me one of their 4B-SST dual-monophonic amplifiers ($3550). I wanted to determine what sonic difference, if any, I could hear between a smaller, 100Wpc integrated amplifier and a larger, 250W power amp from the same company.

I had reviewed various versions of the 4B-SST twice in the past 20 years: for Audio in November 1985, and for Stereophile in May 1992 (Vol.15 No.5) and in October 1999, Vol.22 No.10. The 4B-SST is Bryston's earliest product, first brought to market in 1976. Its reputation for ruggedness and reliability has resulted in its acceptance by recording engineers and touring musicians, and it has done well with audiophiles because of its good sound and its ability to drive difficult speaker loads. The original 4B-NRB was rated to deliver over 250Wpc, both channels driven, into 8 ohms; and over 350Wpc, both channels driven, into 4 ohms. (Tom Norton confirmed these figures in the January 1993 Stereophile, Vol.16 No.1.) The current version of the amplifier, the 4B-SST, is rated at 300Wpc into 8 ohms, 400Wpc into 4 ohms, and over 1000W in bridged monaural mode.

Weighing 44 lbs, the 4B-SST is more massive than the B100-DA SST. It has a 17"-wide silver faceplate, more prominent, rounded heatsink fins, a remote 12V trigger input with delayed output, and selectable inputs for balanced or single-ended input connectors.

Like the B100-DA, the 4B-SST has a separate power supply for each channel, both in a single chassis. Its two separate amplifiers are arranged symmetrically, with every part duplicated, with the exceptions of the single power cord and the bridging-circuit board. Two large toroidal transformers fill the front of the chassis, near the front panel, where they are optimally supported when the amp is mounted in a rack. Output transistors and drivers are mounted in vertical groups of three to the sides and back of the chassis. One PC board in each channel spans two vertical groups and contains the amplifier drive circuitry. Two other boards are hardwired to this drive board. The 4B-SST's construction allows for the entire board assembly to be removed for replacement. Eight 4,700µF filter capacitors per channel are connected directly to the channel-frame PCBs.

The 4B-SST uses a double-complementary differential input circuit. The 4B-SST's output stage has been improved over the years, partially through hand-selecting the bipolar devices, which produces an output stage quite tolerant of loading. It also is said to eliminate all zero-crossing anomalies, including notch distortion.

Listening to the earlier version of this amplifier 14 years ago, I praised its "solid, deep, fast, powerful, and well-defined" bass response, along with its excellent width of soundstage, depth of image, and separation between instruments.

After throwing the B100-DA's rear-panel Connected/Separate switches to disconnect its own power-amp sections, I connected its two preamp-output jacks to the 4B-SST's input jacks. The combination of B100-DA and 4B-SST drove my Quad ESL-989 speakers to produce the same bass slam and snap, the same deep soundstaging, the same separation between instruments I'd heard with the B100-DA alone. Together, the two components were slightly more transparent than the integrated amplifier, but even so, I was hard-pressed to hear any improvement over the B100-DA's extended highs and smooth midrange through the Quads. However, the 4B-SST did play deeper in the bass and had better dynamics when driving the more power-hungry Revel Ultima Salon speakers.

I recommend both amplifiers for use in a high-end system, but the 4B-SST has the advantage when higher sound levels are desired from dynamic speakers.—Larry Greenhill