Bryston BP-20 & 4B NRB amplifiers

This article, written by Malcolm Steward, first appeared in Audiophile magazine (UK) in 1993/4.

 

Technical Intro

The Bryston BP-20 is a line-level only pre-amplifier, although a complementary external phono section, the BP-20P, with an optional moving coil stage is promised. Currently, vinyl users need to connect another phono pre-pre-amp, such as the Bryston BP1 moving magnet phono stage. There’s an additional TF-1 transformer unit for moving coils. The BP-20, bowing to its professional heritage, has both RCA phono – unbalanced – and XLR-terminated balanced inputs and outputs. While the balanced outputs are useful for driving the power amplifier over long interconnects, the balanced inputs are of limited use in the UK. Very few hi-fi manufacturers fit balanced outputs to their equipment although some US equipment has them.

Bryston BP20Bryston’s literature claims that you’ll find no wiring inside the pre-amplifier. I wasn’t able to check this because the case fixings are unconventional Robertson screws for which I don’t have a driver. However, I’ll take it on trust that the components were plugged “directly into glass-epoxy circuit boards, eliminating variations in signal travel and wire interaction.” Great play is made of the unit’s low noise and distortion characteristics with input-to-input crosstalk, for example, being rated as “essentially non-existent” and channel-to-channel interaction being low enough to negate any possibility of component crosstalk. The BP-20 also uses a ground plane to reduce crosstalk and noise throughout the internal circuitry, and the unit’s power supply transformer is in a small, standalone case. Bryston has housed the BP-20 itself in a steel cabinet “for shielding to reduce electromagnetic interference”. Many British manufacturers prefer aluminium cases, feeling that surrounding electromagnetically sensitive components with ferrous cases can introduce more problems than it solves.

The 4B NRB power amplifier is a heavily redesigned version of the long-standing 4B model. Described by its makers as “quite a different animal” to the original, you have to respect the choice of words; different or not it certainly is an animal! Although rated at 250 Watts, its output increases to 400 Watts per channel into a four-ohm load and 800 Watts when it’s used in bridged mode into eight-ohm speakers. The amplifier’s side cheeks are fitted with large heat-sinks and these, along with the other chassis panels, dissipate enough heat to make a working 4B NRB comfortably warm to the touch.

Bryston 4bIt is a completely dual-mono design fed by substantial power supplies. The only shared components in the 4B NRB are the mains lead and the bridging circuit PCB; everything else, including the two large toroidal mains transformers, is dedicated to one channel. Each power supply uses multiple small filter capacitors instead of the more usual single large types. Short wiring leads bring these caps within an inch of the amplifier’s output stages. Bryston claims this supply arrangement improves high frequency performance and reduces losses in the supply.

The regulated supplies are designed to be very “stiff” and their 85V rails reputedly won’t sag even when the amplifier is drawing 10Amps. To prevent this beefcake popping fuses when it is switched on, the 4B NRB uses a soft-start circuit, employing triacs in series with the mains transformers to moderate switch-on current surges. Bryston recommends that the amplifier is connected directly to its own mains socket and not daisy-chained from a power outlet on another component – a practice that’s more common in the US than it is in the UK. The company also discourages the use of line conditioners and filters.

The power amplifier circuits run in conventional class AB mode and employ hand-selected and matched, bipolar transistors, chosen for their linearity, efficiency and reliability. The output stages are designed to eliminate zero-crossing distortion and to be highly tolerant of loudspeaker cable loading. On the subject of reliability, Bryston offers a twenty-year parts and labour guarantee on all its products.

The review proper

Bryston has been designing and building electronics for more than twenty-five years, catering for both the professional and consumer markets. I first came across the Canadian-built amplifiers in the UK a few years ago when turntable manufacturer Roksan was importing them. My reaction then was that their sound quality was good, if not the best I’d heard judged by audiophile standards, but I found their appearance distinctly off-putting. Their countenance was uncomfortably muscular and I’ve never felt attracted to domestic hi-fi that looked as though it would be more at home racked up with a sound reinforcement rig.

However, things appear to have changed on the styling front. Since August 1993, the Professional Monitor Company has been importing Bryston and the amplifiers supplied for review looked far better suited to home environments. The new BP-20 pre-amplifier I’ve been using has an almost subdued appearance, although the company logo still wouldn’t be out of place in a back-line along with Mesa Boogies and Marshalls. The 4B NRB power amplifier – if you ignore its grab handles, which turned out to be quite useful when I was manhandling it – could almost pass for regular, heavyweight hi-fi. What hasn’t altered is the equipment’s rugged feel: the build quality still invites you to stand on the casework.

In use, the amplifiers certainly gave the impression of having a sonic ruggedness to match their external solidity. I started listening to them through the compact Neat Petite speakers, which, in spite of their necessarily curtailed low frequency response, take great delight in exposing amplifier weaknesses. Driven by my Naim CDS CD player, the system, mounted entirely on Mana Acoustics supports, sounded encouragingly clean and forceful with the stack of CDs that have accumulated closest to the CDS over recent weeks. Most of these discs are rock with a belligerent tinge, such as Rage Against The Machine’s magnificently up-yours menage of rap and Led Zep riffs. Music of this persuasion really kicked through the Brystons; the amplifiers’ utter lack of excess flab and sweetness allied with their tight bass and incisive top end allowed the music’s militant mien to come through without any dilution. The 4B NRB’s low end was especially effective in this respect. Bass guitar and kick drum patterns made their presence felt unmistakably without resort to rhythmically destructive overhang or ambiguity. When the onslaught subsided briefly before the final chorus of Take The Power Back, the Bryston showed it could be delicate too, with its deft handling of Brad Wilk’s more restrained cymbal patterns.

The only danger with playing this sort of material through these amplifiers is that moderately efficient speakers begin running out of cone excursion before the BP-20′s volume control hits the half-way mark. It’s frighteningly easy to flick the tiny mute switch on, which drops the level by 20dB, say, to answer the phone, then return and  crank the volume control hard to starboard. Everything sounds normal but then you spot your mistake, restore the switch and, whoa, the Frying Tonight sign above the speakers lights up! With amplifiers this mighty, wise owners will keep their minds focused on what they’re doing.

So, is the Bryston combination all shove and little sophistication? Ears that I respect have levelled that criticism at earlier models. Replacing Rage with Rollins – Sonny Rollins, that is, indicated that the new combination also had a respectable degree of finesse. Listening to the saxophonist playing I’m An Old Cowhand – from the album Way Out West – I was pleased to discover that the Brystons could maintain Ray Brown’s double bass line consistently. Without giving the instrument undue prominence, the amplifiers made sure that note a note was missed, no matter how gently it was played. The same was true of Shelly Manne’s tempered drum patterns; although he was often playing with considered restraint every beat emerged as clearly as if he were pounding his way round the kit in a far more energetic fashion. Without sounding in the least obvious or forced, the Brystons delivered a very detailed account of his playing. Rollins’ sax enjoyed a similarly decisive rendition, again losing none of its detailing or sense of potency when he played quietly.

Although detailed, the Brystons neatly side-stepped sounding like hi-fi. They did not indulge in the initially impressive highlighting of minutiae that I’ve heard in several amplifiers from across the Atlantic. They integrated the constituent parts of the music cohesively into the whole. Detail was there if you were looking for it but it wasn’t thrust out of the music in look-what-I’ve-uncovered trophy fashion. With the sparse arrangements and straightforward recording of Way Out West it’s easy for an amplifier to get involved in the undue highlighting trip but the Brystons stayed as cool and easy-going as the music itself.

At this point I swapped the Neat Petites for the Linaeum LFX Standards, another speaker that’s highly discriminating where amplifier quality is concerned. While the LFXs don’t have the same low end power, they still gave a suitably full-blooded account of the Rollins’ CD. Their hybrid dipole drivers presented midrange and treble information in a very forthright and distinct manner but, again, never came close to sounding artificial or inflated. As with the Neats, it was the music that grabbed my attention. I’ll bet that somebody at the Bryston factory spends his days listening solely to contemporary music – and not the safe, antiseptic variety found on American audiophile labels. The BP-20 and 4B NRB know how to swing, how to treat a rhythm, how to boogie. The amplifiers grasped the character of jazz and rock discs, and clearly conveyed the feelings and expression that performers wanted to convey with their music.

The Brystons were notably successful in this respect. I know that the notion of musicality has been given a thorough kicking by some critics but I’m sticking with it until something better comes along. For example, when I played The The’s Love Is Stronger Than Death, the first thing I noticed was that the hairs on my arms were bristling. The objective, “scientific” reasons why this happened don’t matter; the important thing was that the amplifiers were able to communicate the song’s emotional triggers. The objectivists can enjoy their academic search for technically wonderful equipment, the stereo nuts can chase their pin-point, holographic imagery, but I’ll carry on looking for hi-fi that gives me an adrenaline rush and sends me to bed with a smile on my face.

It’s possible that other listeners, perhaps those with different musical tastes,  might not share my enthusiasm for these amplifiers. I’ll concede that their delivery might be a little too forthright for some, but jazz and rock music are generally vibrant and demanding in the flesh. Some listeners might crave a more “refined” sound and there are plenty of amplifiers that will offer them a polished, more sanitised view of music. There are also amplifiers whose detail retrieval is more overt and painstaking. However, those who want an upbeat, emotionally stimulating, visceral portrayal of music should short-list the BP-20 and 4B NRB for an audition. The combination succeeds in retaining music’s integrity even when it’s driving insensitive speakers to realistic levels, and there aren’t too many amplifiers that find that an easy task.

 Data

BP-20 pre-amplifier

Price:             £1125

Size:             44 x 483 x 280mm (h,w,d)

Inputs:            Bal 1, Bal 2, Video, CD, Tuner, Aux (2)

Headphones:             no

Tone controls:             no

4B NRB power amplifier

Price:            £1756

Size:            133 x 483 x 394mm (h,w,d)

Power rating:            250 Watts (8 ohms)

Speakers:             one set

   DESIGN

  •  Minimalist pre-amplifier and power amplifier combination
  •  Power amplifier can be run in bridged mono mode for 800 watts/channel
  •  Pre-amplifier offers balanced and unbalanced connections
  •  Tape circuits can be used to connect external processors

   PERFORMANCE

  •  Power amplifier copes well with insensitive speakers and reactive loads
  •  System’s headroom and power allows convincing portrayals of large dynamic swings
  •  Bass is tight and dry, which fosters good rhythmic drive and precision
  • Overall presentation is cohesive and favours musical rather than

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