Bryston 7B NRB-THX, ST, & SST monoblock power amplifier 7B-SST April 2003
For the past 18 years, the Bryston 7B-ST, a 500W solid-state monoblock, has been the company's flagship power amplifier. Stereophile praised it in 1996 for "its speed, drive, slam, bass control, and superb control of the mid- and upper bass response" (Vol.19 No.10). The 7B-ST supplied very high power (954W into 4 ohms!) and a powerful bass response for bass-shy dynamic loudspeakers in a relatively small, lightweight, economical (less than $6000/pair) package whose bridged output circuit could be switched into parallel operation to drive low-impedance loudspeakers. Bryston recently extended the technological innovations made in their 14B-SST dual-mono amp to the rest of their product line, and replaced the 7B-ST with the 7B-SST. (The 7B-SST costs $2995, or $5990/pair: $730/pair more than the 7B-ST.) The SST upgrade merited a Follow-Up report, and gave me the chance to revisit one of my favorite high-end audio products.
The 7B-SST is an evolutionary upgrade that preserves the 7B-ST's bridged series-output circuit and single channel, but now comes in a silver, rather than black, chassis. The 7B-SST is 6 lbs heavier and 3" less deep than the 7B-ST, lacking the latter's rear heatsink extension. The 7B-SST's rear panel now has a gain switch to match the unbalanced (29dB) or balanced (23dB) inputs, a power-up switch (marked Local for front-panel control, Auto for turn-on from a switched power outlet), an external control voltage power-up switch, and level controls on the pro version. The 7B-ST's four speaker-binding posts, necessary to permit both series and parallel operation, have been replaced by two posts, conveniently more widely spaced. Inside, the power transformers, bipolar output transistors, and power-supply filter capacitance have been upgraded to SST standards, which were described in detail in the review of the dual-mono 14B-SST in the November 2002 Stereophile (Vol.25 No.11).
The 7B-ST's rear-panel switch for changing the bridged amplifier circuit's configuration has not been retained in the 7B-SST. With this switch, the owner could change the circuit configuration from series to parallel to allow the amp to drive speaker loads lower than 4 ohms. However, the Bryston engineers found that this switch generated a tiny but measurable amount of distortion. Therefore, the 7B-SST is sold in the series or parallel configuration, this factory-only change available via Bryston's Service Department.
The distortion rating has decreased from 0.007% to 0.005% for THD and IM into 8 ohms, 20Hz-20kHz, and the signal/noise ratio has increased from 106dB to 113dB. The power ratings have been increased, both for 8 ohm (600W vs 500W) and 4 ohm (900W vs 800W) speaker impedances. These higher ratings mean a bigger current flow and more heat to dissipate, which required more heatsink area—the number of sinks has been increased from 48 to 64. The 7B-SST's heat-radiating area is 36% greater than the 7B-ST's.
I received a pair of series-configured 7B-SSTs for review. They were a breeze to install. Their front-panel handles, with the weight of the power transformers attached just behind, allowed me to lift the amplifiers out of their shipping cartons and move them into place. Unlike other Bryston amps, however, the 7B-SST has no rear handles, which would have made installation even easier. The rear-panel switches were left in the balanced input, 2V gain, and Local settings for both power-up and external turn-on.
Comparison power amplifiers included pairs of Bryston 7B-ST and Mark Levinson No.436 monoblocks, and a single Krell FPB 600c dual-mono amp. I found it easy to attach my Pure Silver Cable speaker-cable lugs to the 7B-SST's 60-amp-rated binding posts. While being the requisite 19-25mm apart for CE regulations, the amplifier's binding posts are hollowed to accommodate both a single banana plug directly into the post, and one perpendicularly through a hole in the base. The posts themselves are plastic-shrouded so fingers can't come in contact with "live" metal. The slots in the plastic shrouds accommodate spade-lug connectors up to 5/16" thick.
The 7B-SST's turn-on sequence was simple: flip up the rear-panel circuit-breaker switch, then press with a finger at the center of the front-panel membrane switch, as you would a touchscreen cursor control on a laptop. A light touch worked best—the switch didn't respond to the force needed for heavy-duty power switches that do double-duty as circuit-breakers.
On first listen, the 7B-SST was not as fast or as bright-sounding as the Bryston 7B-ST when driving the Revel Salons, was not as shimmeringly translucent as the Krell FPB 600c, and was not as warm and full as the Mark Levinson No.436. Like the 14B-SST, the 7B-SST's character was powerful but polite.
Previously, only the Krell FPB 600c and the Bryston 7B-STs driving Revel Salons could reproduce full-volume percussion music without compression. Take the opening timbales solo of "Tito," on Arturo Sandoval's Hothouse (CD, N2K 10023). Over the 7B-STs, Tito Puente's rim shots were fast and explosive, like gunshots. Like the 14B-SST, the 7B-SST reproduced the rim shots more smoothly, without the speed and glare that had made them so exciting through the 7B-ST in series configuration. Even so, I could easily hear when Puente moved from side to side to play different drums. The 7B-SST easily revealed the different sounds of the drum heads when two different drums were struck simultaneously, although the 7B-ST did a better job resolving this subtle difference.
During the Patti Austin solo, "Only You (No Se Tu)," the 7B-ST gave the singer a pleasing forwardness and presence I didn't hear on the 7B-SST. Although the 7B-ST and 7B-SST sounded almost identical, I had a feeling—more involvement, more pleasure—when I listened to the older amplifier that I couldn't explain, defend, or immediately understand. I was surprised by this.
This subtle feeling became clearer only with repeated comparisons. Soloists, including Harry Connick, Jr., Mary Gauthier, and Emmylou Harris, sounded more open and extended through the 7B-ST, even though they showed slightly less strain with the 7B-SST. The older amplifier was slightly brighter and more forward, the newer was more neutral, as neutral, in fact, as Bryston's new 14B-SST stereo amplifier. This neutrality helps the amplifiers get out of the way of the music but defies easy characterization, and initially was not very involving. It took some time for me to warm up to the 7B-SST. In the end, I came to rely on the 7B-SST as a courteous guest who didn't impose but always had clear, unbiased opinions.
Like its predecessor, the Bryston 7B-SST is a beefy, rugged, reliable audio product whose 20-year warranty and $5990/pair price make it a terrific value. Its power and headroom ratings are greater than those of all but a handful of more expensive flagship monoblocks, including Krell's FPB 650c and Master Reference Amplifier and the Mark Levinson No.33.
The 7B-SST retains the 7B-ST's incredible deep-bass abilities, making it the obvious match for bass-shy floorstanding speakers. It also has terrific soundstage depth and midbass punch. On a handful of recordings, I was able to detect more transparency and openness driving the Revel Salons with the 7B-STs, although the 7B-SSTs were smoother, more neutral, less harsh on peaks.
You, too, might find the neutrality of the powerful Bryston 7B-SST a welcome addition to your system.—Larry Greenhill