Bryston BP-25MC/7B-ST
VACLAV SKARDA, PAVEL DUDEK

The Bryston company, whose products recently appeared on our market, is based in Canada and produces very high quality preamplifiers and amplitiers and also the protessional audio products. The combination of the BP-25MC preamplifier and 7B-ST monoblocks (with 500W/8( of output power), a subject of this review, is basically its flagship amplifier product. In the information materials of Bryston, though, it is not considered as anything special. It is just the application of the basic Bryston construction philosophy, which is also contained in the lower models, tor the very high power output and excellent sound. In the commentaries and explanations of the Bryston designers, you will not find anything about magic connections and special circuits, which will allow listener to reach unheard of levels of sound quality. It is more probable that you learn something about the minimization of the noise levels and all kinds of distortion, about the optimization of circuits and about the emphasis on the product reliability. As a proof, there is the full 20 year transferable warranty on all Bryston products.

The current, fifth generation of Bryston amplifiers carries the ST label, which are the initials of Mr. Stuart Taylor, Bryston designer, who is the author of the most recent important design changes. The new series started quite innocently, when Stuart Taylor was assigned to redesign the 8B, the Bryston four channel power amplifier. The simple positioning of the transformers horizontally turned into the complete redesign of the signal paths, which resulted in much better measured parameters as well as the sound quality. The circuit design changes were subsequently applied to all Bryston power amplifiers. The preamplifiers were also redesigned. Stuart Taylor used specialized measuring equipment for finding and eliminating the sources of noise, distortion and ground loops. The result was again much lower noise and distortion levels and better sound quality.

At the end of the introduction, I would like to direct your attention to the interview with Bryston chief-designer Chris Russell in the corresponding section of the magazine, and now, I will pass the word to Pavel Dudek, who prepared the technical part with its own introduction.

Technical description

I really like the recordings of the American company Telarc, because they really excel in the absolute correctness and naturalness of the recorded sound. It doesn't matter if you listen to the symphonic orchestra, string quartet or jazz recording. The whole production is excellent. Sound engineer Jack Renner doesn't take any chances with the recording (as my musician friends explained to me in detail) and very carefully chooses the components of the recording chain, which are subsequently quoted in the CD booklet. Mr. Renner originally used the Threshold and krell amplifiers, recently, though, he started to use the products of Bryston. Yes, my friends, not any super expensive components (even if the price is not usually the issue, because the companies are proud to lend the product for free), but the relatively inexpensive components of this Canadian company. I did not know why, but now, after the personal experience with Bryston products, I understand Mr. Renner. The reason is the absolute sound neutrality and excellent resolution of detail.

7B-ST Monoblock

The 7B ST power amplifier is of the bi-monaural construction. It means that everything, which handles the analog signal, is totally separate for each channel (two power transformers, two rectifiers, independent capacitors). Why is everything doubled in the monaural amplifier? I will explain later.

If the amplifier does not have separate power transformers, it is not dual-mono, as is often quoted i.e. on Sony or as my colleague Kraut wrote in the Accuphase P450 review. Bi-monaural is not also the amplifier with the separate secondary windings on the power transformer.

It is important to emphasize the advantages of the hi-monaural construction. When the audio signal is reproduced, the power output modulates the DC voltage of the power supply. If the power supply is common for both channels, this modulation is transferred to the other channel and vice versa. The result is higher cross-talk and subsequent deterioration of the localization of the sound images. A bit better solution is the aforementioned use of separate transformer windings for each channel. You can easily recognize this type of amplifier by two pairs of capacitors and two rectifiers in the power supply. If the amplifier has only two power supply capacitors, you cannot speak about bi-monaural construction at all (P-450).

Bryston 7B-ST is a monaural amplifier, which enables two modes of usage. The first one is described by the manufacturer as Serial, which is only a different description of the usual bridged configuration. In this mode, the two amplifier sections are driven by the signal in opposite phase and the load (speaker) is connected between them. The second mode, Parallel, enables the paralleling of both modules for much higher current delivery. It means that the amplifier will be able to work into substantially lower load impedance.

7B-ST is basically the modification of the already tested 4B-ST. The major difference is, that it is permanently connected for mono operation (serial or parallel, see above). The second pair of input terminals on the back is therefore missing. The input is switchable for non-symmetrical (gold plated RCA) or symmetrical (XLR/Jack - Neutrik) connection. The outputs are five way binding posts with gold plated contacts. Between them is the isolation ridge which prevents the short-circuit by bare wire. Nice touch. The power cord is three-prong, the component therefore works in Safety Class I. But, it is possible to disconnect the working ground of the amplifier from the chassis using the switch on the back. The ground is not disconnected completely, but through the 10 Ohm resistor, which is sufficient for the elimination of ground loops possible when connected to other equipment working in the Class I. Using the usual "cheater" plug is much more dangerous.

The amplifier modules, placed vertically on their heat-sinks, are connected to the power supply via heavy-duty PCB connectors. The power transistors are handmatched, each driver - output pair is handled as a composite output element in the "Quad-complementary" configuration.

Worth to mention is the clipping indicator on the front panel. The green LED, which indicates the power-on and normal operation, turns orange when approaching clipping and to red from 1 dB in clipping and up. The indication is very fast and accurate over the whole audio band. I would like to mention, too, that the entire amplifier is hand-soldered, which is at the price and "Made in Canada" quite unusual.

BP-25MC preamplifier

The BP-25MC preamplifier is constructed in the similar fashion as the power amplifiers. It means very simply and efficiently, nothing unnecessary. With the exception of the phone modules and small PCB, carrying the unbalanced connectors, it is placed on one high-quality one-sided circuit board, which covers the bottom of the chassis. Everything is hand-soldered. To the preamp, five unbalanced (including phone cartridge) and two balanced sources, can be connected. All contact surfaces are gold-plated. The preamp has two unbalanced and one balanced output, one tape loop is available.

The line amplification for the BP-25MC is provided by discrete amplifier modules, three per channel. Two of these op-amps are to buffer the signal to the tape output and level control, the remaining four for the two balanced outputs. These proprietary circuits are specified as delivering high output with low noise. The input signal is switched using the multi-packet switch (Lorlin), volume control is a blue motorized ALPS potentiometer, 10 k(. The outputs are connected by relay, which switches on with delay after power-up to avoid the surges. It is also used by the Mute function. The absolute polarity of the signal can also be switched. Both these functions and the volume are available on the remote control, which has sturdy metal case. There is also headphone output on the front panel.

It is important to note that there are no integrated circuits in the signal path of the preamplifier. All gain stages are based on the proprietary discrete operational amplifier in balanced configuration. The circuit is the simplest possible. i.e. differential amplifier, voltage amplifier and emitter follower, everything, of course, complementary. The operational conditions are set for class A operation, the output transistors therefore run quite hot. The already low DC offset, which is typical for this kind of connection, is eliminated by the bipolar capacitor at the output amplifiers.

The phono stage uses similar topology as the line inputs. The stage uses the so-called half-passive RIM equalization. The basic configuration, i.e. two gain stages with the equalization between them and in the feedback loop, is used for the MM cartridge. For MC, high-quality step-up transformer is used, which is the best solution for high signal to-noise ratio. The preamplifier has an external power transformer, the power supply itself is shared by both channels.

Conclusion:

Sound quality

The judgment of the sound quality of reference amplifiers is not an easy task for the reviewer. On the other hand, the first acquaintance with such a product is an interesting experience for the newcomers to the high-end audio world. Some things are very easy to realize in the first listening, but very few, even experienced listeners are capable of such immediate subjective characteristic of a product, that they will not need to change anything in it after long-term listening.

When the consumer is choosing the amplifiers by listening to them in studios, there is an advantage for the products with an interesting sound characteristic. The problem is, though, that this "interesting" characteristic may be caused by some kind of distortion, which may result in unpleasant feelings after long-term listening. The amplifier, which noes not distort the signal in any way, may be not that attractive at the first listening.

The amplifier combination under test can, because of its absolute neutrality, easily fall into this category. There is, though, one characteristic, which will catch even inexperienced listener on the first listening (when using appropriate speakers), and that is the reproduction of bass. Major role here is played, of course, by the 7B-ST monoblocks. In the bass, reproduced by this amplifier, there is a clear physical feeling of the extension to the lowest of the low frequencies, without any boominess in this region (the measured frequency response is, of course, ruler flat). The result is (with the speakers possessing the appropriate bass extension) the much increased feeling of the presence in the original recording space, as a result of the reproduction of the "air movements" in it. The bass tones itself, one octave higher, are reproduced with very fast attack and also decay of the tone.

To describe the characteristic of this amplifier at the most important mid-frequencies and highs is not an easy task. The reason is that especially after a long-term listening, the characteristic signature is surfacing here, and it is the absence of any sound distortion or coloration. And this is for any listenable sound level (at least in smaller listening spaces). The listenable sound level, though, has a bit different meaning with this amplifier. When I listened to a rock record Soundgarden -Superunknown, I found myself dragged into the music and turning the volume up. Suddenly, I got a feeling that I must be playing really very loud. I switched on the sound level meter and measured the average level at 115 dB. But the sound was still very clear without any trace of distortion or dynamic compression. When I turned the volume a little bit more, the speakers produced audible distortion, but the amplifiers never reached clipping.

The amplifier has a very clean upper frequencies and you cannot ascribe any characteristic signature to the midrange. When you listen to a well recorded rock recording, it is a real pleasure to sense i.e. the beautiful sound of the Fender Stratocaster with its characteristic signature. With classical, it was very easy to distinguish the quality of a recording by the sound of a violin. The listening to the famous Frank Zappa - Yellow Shark was an ultimate listening experience. As far as the soundstaging is concerned, you can feel again, that it is defined essentially by the quality of recording, without any added phase anomalies. Each sound image is very clearly defined and positioned, the whole presentation is very natural.

Another typical characteristic, which I never experienced before, is the total "blackness" after each reproduced tone. You can hear only the tone itself and nothing, what would follow it, be it some noise envelope or the sign of distortion. Dynamic capabilities of the amplifier, its speed and timing accuracy are truly excellent.

The phono section of the preamplifier had enough gain even for the low-output Ortofon MC-3000 and its sound characteristic was also excellent.

Conclusion

By acquiring the combination of Bryston 7B-ST power amplifier and BP-25MC preamplifier, the audiophile receives the amplifier with reliable, precise construction, in which everything is dedicated to one goal - undistorted reproduction of music.

Over time, I had the possibility to get acquainted with many high-end amplifiers of the worlds finest audio companies. All these products performed truly excellent, but later I realized that each of them possessed some characteristic signature. Majority of the sound attributes were excellent, especially the bass of the big amplifiers. But in some areas, the deviation from the totally transparent behavior could be found. In the worse case it was the trace of grain or hardness in the top midrange and highs. Or, on the better side, the smoothness or warmness of the midrange, which eventually comes up also as a distortion. With the latter type amplifier, it is easy to become used to this type of distortion and still judge it as the ultimate.

When using the Bryston BP-25MC/lB-ST amplifier, I did not find any such sound deviation. I can say with no hesitation that, to the person, who is interested in really undistorted sound reproduction without embellishments, and does not need to warm up his room (by the Class A amplifier), this amplifier combination is the end of the road.

Measurements

In the last issue of our magazine, we got acquainted with the Bryston company and its standard amplifier models, the 49-ST power amplifier and BP-4 preamplifier. Their advantages, rational and robust construction, high power and very good measured parameters are further developed in today's models. The power part is handled by two monoblocks, each capable to deliver the amazing 900 W into 4 ohms. It is very improbable that this amplifier will ever be working at the clipping in the domestic conditions. As a result, the possible problems in clipping is not necessary to take into account. The very high power is attained by the bridging of two identical amplifiers.

The static and dynamic parameters of amplifiers are very good a do not differ considerably from the previously measured models. The slew rate is 65 V/(s, high damping factor is less frequency dependent, The response to the 3.1 5 kHz square-wave signal just before clipping is on the Fig. 1 (the black line is for the nominal 4) load, the red for complex load and the blue shows the ideal response). On Fig. 2, the 10 kHz sine wave at the onset of clipping, is depicted (red line, the blue line is the ideal shape). The differences between the measured and ideal curves are discernible, but not significant. They will not have an influence on the signal quality.

Conclusion:

The combination of the 7B-ST monoblocks and BP-25 preamplifier is very-high-power amplifier unit which can be used for the high quality amplification also in large listening environments.

We invite you to experience the Bryston SST² Series amplifiers

20 Year Warranty - A Generation of Music