Interview with James Tanner of Bryston

June 30, 2010


James Tanner of Bryston was gracious enough to consent to an exclusive interview with the Ultra High-End Audio and Home Theater Forum which is set forth below.

Thank you for agreeing to be interviewed for the Ultra High-End Audio and Home Theater Forum again. Bryston has long been known for its power amplifiers, but it has branched out recently to offer power conditioners at one end of the spectrum and digital components at the other. Let me begin by asking you to describe your Torus line of power conditioners.

Firstly, let me explain that Plitron, one of the world’s most respected transformer manufacturers based here in Canada, builds the Torus Power products. Bryston has been involved in the design concept from the start with Torus, and we also handle worldwide marketing for Torus Power. As an amplifier manufacturer, Bryston always advised consumers NOT to use an AC conditioner because such devices can limit the transient response of an amplifier by limiting the instantaneous current draw —then we began thinking: What would be the perfect power source for an amplifier? How could we make the perfect conditioner? We concluded that the ideal device would be a very low impedance AC source with high current capability. That led us to the concept of using huge isolation transformers, which have an impedance of .2 to .04 Ohms. By comparison, a typical AC wall outlet has an impedance of about 1.5 Ohms—significantly higher. Additional benefits of isolation transformers: they provide total isolation from any noise on the power grid because nothing is in ‘series’ with the wall plug. Your equipment works off the MAGNETIC field between the primary and the secondary of the isolation transformer.

What are the advantages of balanced power?

Balanced power provides effective noise filtration through common mode noise reduction. This is a very misunderstood area when it comes to power line conditioning products. For an in depth discussion, please refer to our white paper titled Understanding Balanced Powerline Conditioners.

If I remember correctly, your Torus power conditioners employ series-mode surge suppression. How does series-mode surge protection differ from traditional methods of surge protection, and what are its advantages?

The Torus series-mode technology does not shunt to ground and it is not a “sacrificial” device like MOV’s, which often fail after one power surge. Torus units are built to meet 6000 volts, 3000 amps at 1000 repeats.

Do your power conditioners limit current? This is a question of vital interest to many of our members whose systems include large power amplifiers, including those of Bryston.

Size matters—based on our research, we found many isolation transformers used for this application were simply too small and as a result, caused current limiting to occur. Torus uses transformers that are capable of no less than double the rated current, and this design parameter is in place specifically to prevent any current limiting.

In what ways are the benefits of your power conditions audible?

We have found through listening tests and the feedback of independent reviewers that the Torus products help the amplifiers reproduce fast transients, delivering improved control over loudspeakers. The devices also improve the level of audible detail in recordings by reducing background noise significantly.

Turning to your digital offerings, would you describe your new BDA-1 digital-to-analog converter.

When we look back at how we designed our CD player and our DAC, most such devices use one of a handful of premium quality DAC chips. We tested 4 or 5 of them, and found that the differences were there but immensely subtle. The Bryston engineering team focused on power supplies, ground planes, and analog circuitry in order to create outstanding products in our digital lineup.

What DAC chip did you select, and what sonic advantages does it offer?

Bryston settled on the Crystal CS-4398—we felt that it was the most appropriate choice for the circuitry we had designed in our digital products and we already had an excellent history with the Crystal DAC, having used it already in our BP26 preamplifier and B100 integrated amplifier.

I note that the BDA-1 both oversamples and upsamples. There has long been confusion over the difference between the two. Would you explain what each process does and how they benefit the sound of digital playback?

Upsampling: Bryston’s upsampling circuitry and be selected “on” or “off” by the user. The SYNCHRONOUS upsampling circuit (sample rate converter) converts the digital signal from one sample rate and bit depth to another. In the BDA-1 the sample rate is increased from the input sample frequency. If 32K, 48K or 96K it upsamples to 192K. If 44.1K or 88.2K it upsamples to 176.4K. The 16 bits of depth (the CD standard) is increased to 24 bits. The added 8 bits are filled with placeholder information. This upsampling process provides a digital signal for later conversion to analog by the Crystal 4398 DAC chip. The upsampling process doesn’t add any new data to that which came off the CD or computer but it puts the data in a form which can better be used by the DAC as described below. The advantage of this synchronous upsampling process is better processing of the upsampled signal by the DAC chip. These devices were designed for these higher sa mple rates and bit depths and perform better when they are supplied. There is also a noise shaping process implemented where noise from the audible spectrum is being shifted up to frequencies above audible limits. An added advantage of this up-sampling process is that a totally new clock signal is applied which results in a significant reduction in jitter.

Oversampling: The CS-4398 operates in one of three oversampling modes based on the input sample rate. Single-speed mode supports input sample rates up to 50 kHz and uses a 128x oversampling ratio. Double-speed mode supports input sample rates up to 100kHz and uses an oversampling ratio of 64x. Quad-speed mode supports input sample rates up to 200 kHz and uses an oversampling ratio of 32x. This again allows for filters, which are out of the audible range. The output of this process is a sensitive analog signal. The timing of this process must be very closely controlled by a low jitter clock.

The S/PDIF and AES/EBU digital inputs on the BDA-1 are transformer coupled. Would you explain exactly what that means and why it is beneficial?

Basically, a transformer coupled SPDIF connection provides electrical isolation between the transmitter and receiver. A transformer will provide better impedance matching, RF CMR, high-pass filtering and eliminate ground loops, reducing jitter.

The BDA-1 can handle high resolution digital signals up to 24-bit/192kHz. Some question whether the difference between 24-bit/96kHz and 24-bit/192kHz is audible. What is Bryston’s opinion on this issue, and describe what an audiophile should listen for to detect such differences.

My feeling is that the quality of the initial recording outweighs the importance of the digital resolution specs. I have heard wonderfully good recordings 24/96 and mediocre recordings at 24/192, so clearly there are other factors involved. All things being equal, higher resolution recordings typically have a sense of ease and flow about them – they sound less HI-FI and more organic.

The BDA-1 allows you to toggle upsampling on and off. Under what circumstances would you not want to upsample the input?

Upsampling requires a lot of “mathematical processes,” and many people prefer not to alter the original recording format. With the Bryston BDA-1DAC, they can easily try both playback modes. The theoretical advantage of upsampling is that it moves the need for sharp high frequency filters further up the frequency ladder so there is less ringing in the audio signal.

The resolution of the USB input is limited to 16-bit/ 48kHz. Is that a limitation of the USB interface?

Yes, based on the limitation of the USB chips on the market today. It is Bryston’s choice to wait and see what USB chip technology develops in the future before leaping to make any upgrades available. One advantage of the USB input on the BDA-1 is that it receives the digital bitstream as a I2S signal not an SPDIF signal which eliminates one conversion process. Then we upsample that signal (assuming you have the upsampling button pushed) with the state of the art upsampler in the BDA-1. Bryston recommends the use of S/PDIF and AES/EBU digital inputs and a quality sound card for best performance.

Would you describe the features of the BCD-1 CD player?

Our design philosophy right out of the gate was: How can we optimize Redbook CD playback? There are thousands of CD players on the market to choose from, and (as with our BDA-1 DAC) we felt that our attention to power supplies, ground planes, and analog circuitry would make our CD player stand out.

Since the BCD-1 incorporates many of the features of the BDA-1, let’s focus on the transport section of the player. The BCD-1 is limited to CD playback. What factors lead to your decision not to incorporate SACD playback?

The available SACD drives were really DVD drives and had clocking frequencies that were not a multiple of the CD Standard 44.1 and we really did not want to have to manipulate different clocking frequencies to get back to the 44.1 reference point for Redbook playback.

Have you taken any special measures to reduce vibration in the transport mechanism?

Bryston selected a Philips drives known for reliability, longevity, and quiet operation. We felt that this excellent quality drive was ready “as-is” for the Bryston BCD-1, which has been designed to deliver superb playback quality and enormous value as an audiophile CD player.

What is the importance of power supplies in a CD player? For example, do you use separate power supplies for the transport and DAC sections?

Bryston’s design has always been to provide separate power supplies for analog and digital circuits to prevent noise contamination between digital and analog signals, and this philosophy has been extended to include separate circuit boards and other isolated circuit topology that accounts for the BCD-1’s stellar performance.

Jitter is always a hot, and hotly debated, topic among audiophiles. Tell us how you have addressed the issue in both the BDA-1 and BDC-1.

Bryston’s jitter numbers (measured both by us and by independent reviewers) are at the extreme low end of the measurable scale and in comparison with other cost-no-object audiophile players—we put tremendous emphasis on this aspect of our digital designs. Jitter is a mistiming of the digital signal—we made certain that the master clock and the drive of the Bryston BCD CD player are synchronized perfectly to eliminate any possibility of jitter affecting the sound quality of the player.

Do the BDA-1 and BCD-1 carry the same 20-year warranty as your power amplifiers?

All Bryston digital products carry a 5 year warranty.

Is there anything else you would like to tell us about the BDA-1 and BCD-1?

Obviously, we are well aware that the BDA-1 DAC is a product category that is at the leading edge of today’s technology curve while the BCD-1 CD player represents a product category that is in the twilight of its popularity curve. That being said, there are millions of CD’s out there and many consumers want quality playback for their collections that are their primary source of entertainment media. For the future, Bryston is exploring a drive-only product to mate with the BDA-1 DAC, but this will only be addressed once we have finished and delivered the long awaited SP3 HDMI surround processor.

Thank you again for joining us today.