Bryston BP-173 line preamplifier

Each equipment report in Stereophile focuses on a single audio component. When listening to a component for review, I leave unchanged all other components in my audio system. Other Stereophile reviewers experiment with different interconnects, speaker cables, power cords, or stands. As I found while reviewing Bryston's BP-173 (Cubed) preamplifier, being flexible has its rewards.

My first lesson in flexibility was learning what Bryston means by "Cubed" (footnote 1). Jim Tanner, Bryston's VP of sales and marketing, explained that all their Cubed models employ an array of 12 active devices for the first 6dB of gain. Developed by the late Dr. Ioan Alexandru Salomie, this array acts as "a super-linear" input buffer to filter out audio- and radio-frequency noise, particularly anomalies that originate in the power line, reducing the overall noise and distortion to less than 0.001%.

The BP-173's base price of $3995 positions it between two other line-level preamps from Bryston: the entry-level BP-6 ($3295) and the flagship BP-26 with MPS-2 power supply ($5390). The BP-173 is 2.30" taller and 2" deeper than the two-chassis BP-26, and improves on the original BP-17 with an extra pair each of XLR and RCA outputs.

The BP-173 is entirely solid-state. It has seven inputs—five single-ended (RCA), two balanced (XLR)—as well as balanced and single-ended outputs. There are pushbuttons on its front panel for selecting inputs, Power, Mute, Bypass, Record, and Balance. Also on the front panel are an IR receiver, a headphone output jack, and a large volume knob.

The rear panel is divided into four sections: Outputs, containing two balanced XLRs—optionally, one of these can be configured as fixed-output, for use with Bryston's BHA-1 or any other balanced-input headphone amplifier—a fixed-level RCA, and variable preamplifier; Inputs, comprising two pairs of balanced XLRs, five pairs of single-ended RCAs that, with the optional modules, can be used as analog or digital inputs, Control, which includes two trigger outputs, an auxiliary IR input jack, and an RS-232 jack; and an IEC inlet for the detachable power cord. Centered at the top of the rear panel is a knurled grounding post for a turntable.


The BP-173's motherboard takes up the entire width and half the depth of the interior, though its front half is unoccupied save for a beefy toroidal power transformer and the power-supply components, to isolate them from the audio circuits on the rear panel. Along the inside of the rear panel, several vertical daughterboards are plugged into the motherboard to handle input and output functions. The components of these wave-soldered printed-circuit boards are surface-mounted and labeled.

The BP-173 can be operated using Bryston's BR2 universal remote-control handset, which costs an additional $375. It has 34 pushbuttons in eight rows and worked beautifully, controlling all functions available from the front panel and more, including phase and unity bypass for home-theater mode.

Like the remote, many of the BP-173's desirable features are available only Ö la carte. The bad news is that this makes the base price deceptively low; the good news is that you can custom-design a BP-173 to have only the features you actually want, without paying for those you don't. Modules for an internal D/A converter or moving-magnet phono stage cost $750 each. The digital D/A module adds four digital inputs; the phono module works only for MM cartridges (footnote 2).

Installation was simple. I placed the BP-173 atop my Salamander Designs Synergy S-40 Open Rack system, used its XLR jacks to make balanced connections from my Bryston BDA-3 DAC and to the Constellation Stereo 1.0 power amplifier, and its RCA jacks for connections from my Day-Sequerra 25th Anniversary FM Reference tuner and Sutherland Engineering Vibe phono preamplifier. I kept track of the numbers of the input jacks on the rear panel, as these match the labels under the corresponding buttons on the front panel. I plugged one end of the BP-173's power cord into its rear-panel inlet, and the other into my Torus Power RM40 line conditioner. I initially connected the ground lead of my Linn LP12 turntable to the ground post on the Bryston, but detached it when it produced lots of hum. I used no decoupling feet, isolation platforms, or other accessories.


My digital sources were Bryston's BDP-3 media player and BCD-1 CD player; all digital-to-analog conversions were done by the above-mentioned Bryston BDA-3. Bryston's detailed, well-written manual doesn't state that the BP-173 needs any warm-up or burn-in; sure enough, I heard no change in its sound quality during the time it spent in my system.

My Revel Ultima Salon2 loudspeakers were placed to each side of my equipment rack, 2.3' from the front wall, 6' apart (measured from the speakers' tweeters), and 6' from my listening chair. This produced optimal imaging and soundstaging—in short, most of my listening to the BP-173 was done in the nearfield.

As always, the first thing I listened to was Stevie Nicks's smoky rendition of "Silver Springs," from Fleetwood Mac's The Dance (CD, Reprise 46702-2). Immediately, I knew something was wrong. Nicks's voice sounded etched and edgy, with more midrange presence than I know it should have. Cymbals and guitar overpowered John McVie's bass line and Mick Fleetwood's kick drum. Gone was the addictive tonal balance I'd heard through the pairing of Constellation Inspiration amp and Bryston BP-26/MPS-2 preamp. Instead, the upper midrange and lower treble dominated the rest of the audioband.

Footnote 1: In Bryston's model nomenclature, the product's model number (eg, 4B) remains the same over the product's lifespan (the original 4B came out in 1978), but each new version gets a new modifier (eg, 4BST, 4B2, 4B3). Bryston's vice-president of marketing, James Tanner, explained: "Things began with 'NRB,' which we started using when we introduced a new series of amplifiers. The shipper wanted to make sure he did not mix up the older stock with the newer, so he wrote 'NRB' on the new retail boxes and 'NPB' on the new pro boxes. The next batch of amplifiers was named for designer Stuart Taylor ('ST'). This later became 'SST' (Super Stuart Taylor). SST was shortened to 'squared,' so the 4B amplifier was renamed the '4B2.' The naming of our latest group of products, with the Salomie input circuit, used 'Cubed' as a natural progression. What's next? 'Quattro!'"

Footnote 2: Following this review, I sent the review sample of the BP-173 back to Bryston to have the optional DAC and phono modules installed. Watch for a Follow-Up.

Bryston Limited
677 Neal Driv
Peterborough, Ontario K9J 6X7
(705) 742-5325

Ortofan's picture

... "superbly well engineered" and "it is difficult to see how a preamplifier could perform any better on the test bench", is it sufficient to derive the full benefit of 24-bit hi-res recordings?
A noise and distortion level of 0.001%/-100dB is barely equivalent to 16-bit resolution. Even the -120dB level only equates to about 20-bit resolution. The LSB for 24-bit encoding is on the order of a level of 0.00001%/-140dB. Does any preamp come close(r) to achieving this level of performance?

dalethorn's picture

Mind-boggling. So whatever the preamp is capable of with the best-case 1 khz test tone, you run a typical 24-bit recording through it and try to hear the preamp's contribution to the sound? No argument here, just trying to imagine how all that breaks down in the real world.

Gnib's picture

I`m very curious about this follow-up on the DAC and phono modules.

dalethorn's picture

"Cubed models employ an array of 12 active devices for the first 6dB of gain. Developed by the late Dr. Ioan Alexandru Salomie, this array acts as "a super-linear" input buffer to filter out audio- and radio-frequency noise, particularly anomalies that originate in the power line, reducing the overall noise and distortion to less than 0.001%."

Well, I thought Ortofan's questions were simple enough, but the array (no pun intended) of issues aren't going to make things easy. Ignoring any photo stages (can I?), the "array of 12 active devices" acting on the "power line anomalies" is interesting. I'd prefer to filter my power elsewhere, but who knows? Maybe these guys have tricks that their competitors don't.

allhifi's picture

Cubed's IBG (Input Buffer/Gain) circuit may be advantageous in main amplifier stages but may not be particularly suitable for preamp's 'Input' stage.

Bryston's 'Cubed' series amplifier's clearly have an articulation/ resolution capability previous series lacked.

Interestingly, the "SST" series was a MAJOR improvement over ST series, but by many accounts, the SST2 was a step back?
Apparently, changes were made to the 'Input Stage' in the SST2 -not well received by many accounts. Yet it "measured" better to Bryston ! Go figure.
Come (near) full-circle, the new "3" series employs a circuit that, interestingly, has Bryston talking 'audiophile' language previously dismissed as superfluous, imaginary -not relevant/important -or "measurable" Go figure.

I suspect IBG-circuit doesn't correlate well in line-stage applications.
While many line-stage (preamp) designer's appear to be employing lower-and-lower gain 3,6, 9 db., Bryston continues with 12-18 db.? designs.

Stick with the 3B/4B3 (Cubed) amps; quite an accomplishment for Bryston.

peter jasz

allhifi's picture

dalehorn: I suspect you are referring to Bryston's noise level/vs./source resolution ?

If so, the "breakdown" in the real-world is obvious via listening evaluations.


dalethorn's picture

Interesting - In any case, these proprietary techniques don't reveal enough to do much besides just listening for any anomalies. If I were engineering these things, I'd like to explore ways to both shape and filter noise (if that makes sense), to try to make it less apparent psychoacoustically. How that would look from a whole-system perspective I have no idea.

allhifi's picture

Indeed, what you say makes complete sense (re: noise attenuation)

It's unclear why makers don't consider using 'Balanced' power/ transformers in their designs -or AC Re-generation, as noted in ML's No.52 preamp.

The Balanced (Symmetrical) AC power supply I'm using (Blue Circle MR-800/1200) offers up excellent 'performance' with any/all components connected/powered. (I use on for 'sources', the other for amplification)

I have recently acquired an Exact Power SP-15 -sitting idle currently.
The SP-15 has a single, substantial 1.8-2KVa that may prove beneficial for main amplification -eventually to replace the 1200 watt Blue Circle.

The improvements in (particular lower/mid frequency) resolution is dramatic, and most welcome -when compared to wall AC power.

Yet, at busy AC-usage times of the day, one can easily hear the polluted line's impact upon SQ; a lumpy, slow sound. It happens regularly.

I suspect an AC Re-generator (PS Audio P-3) would work extremely well in low-power applications, particularly 'digital' gear where SQ improvements are incredible.