Bryston BDA-1 D/A converter

In February 2009, I reviewed Bryston Ltd.'s first CD player, the $2695 BCD-1, and was very impressed by what I heard. The BDA-1 ($1995) is the Canadian company's first standalone DAC. It's slim, only 2.75" high, with the engraved company name, model number, and infrared sensor grouped at the extreme left of a front panel of polished aluminum. Farther to the right are two columns of four LEDs each that comprise the sample-rate indicator, which identifies the selected input's signal frequency and whether the BDA-1 has locked to it. Closer to the center is the Upsample control, which governs the conversion of the incoming digital signal synchronously to 192kHz or 176.4kHz. The Upsample LED turns green for 192kHz, red for 176.4kHz. Digital sources are selected by pressing one of eight pushbuttons just right of center: two TosLink, four S/PDIF (coaxial), one AES/EBU XLR, and one USB 1.1, the last accepting only signals with sample rates at or below 48kHz. An LED above each pushbutton lights green for an incoming PCM datastreams and red for other types, including multichannel Dolby Digital streams.

All of these functions, and the BDA-1's output level, are accessible from Bryston's BR-2 remote control (a $350 option). The BR-2 also can control Bryston's BCD-1 CD player, BP26 preamplifier, and B100 SST integrated amplifier. The remote automatically lights up when you pick it up in a dimly lit room.

On the rear panel, starting from the left, are: balanced and single-ended pairs of analog audio outputs; a single S/PDIF output; a single USB input; an AES/EBU XLR input; four S/PDIF inputs; two optical TosLink optical inputs; a two-pin trigger input to facilitate remote hardwired on/off control; an RS-232 port for uploading firmware; and an IEC 320-C14 power inlet to mate with an IEC-320-C13 AC mains cord.

Internal Details
Just behind the rear panel is the full-width, multilayered printed circuit board that carries the D/A and analog stages. I wasn't able to get inside the chassis because I didn't have a driver that matched its Torx #8 screws; however, the BDA-1's brochure includes a clearly labeled view of the BDA-1's innards. Most of the interior is empty space, with a single ribbon cable joining the circuit board to another behind the front panel.

Starting at the left of the main board are separate toroidal power transformers for the analog and digital power supplies. Nearby are multistage voltage regulation and filtering components, including electrolytic capacitors and a row of heatsunk voltage regulators. Each stage (input receiver, sample-rate converter, DAC) is independently regulated to prevent interaction and to minimize jitter. Careful trace routing is used to reduce the risk of capacitive coupling to achieve greater reduction of noise and distortion, especially for the low-voltage analog signal leaving the DAC. In the center is a Burr-Brown SRC4392 sample rate-converter chip, to the right of which is a pair of DAC chips, these 128x-oversampling 24-bit delta-sigma Cirrus CS4398s, the same as used in the BCD-1, though only one chip is used in the CD player. Finally, on the far right are four rows of components that comprise the discrete analog amplifier's output stages.

Bryston describes the PCB as being constructed of double-sided epoxy glass with clearly printed component markings. All the components are surface-mount types, and high-quality, 0.1%-tolerance metal-film resistors and polystyrene capacitors are used. Soldered and other gas-tight mechanical connections are used for the signal circuits. Bryston's warranty is five years for the digital circuits, including parts and labor, and 20 years for the analog circuits.

Design Considerations
One of Bryston's primary goals for the BDA-1 was to reduce clock jitter, ie, mistimings of the digital datastream presented to the DAC. Unlike the company's BCD-1 CD player, a one-box transport and DAC, the standalone BDA-1 must reclock all signals fed to its data inputs. To maintain timing accuracy, the Bryston engineers used three different methods of maintaining accuracy and keeping jitter to a minimum: impedance-matching transformers to provide the best interface possible, reclocking the signal, and synchronously upsampling the signal.

The BDA-1's Burr-Brown SRC4392 sample-rate converter provides synchronous upsampling: 32, 48, and 96kHz data are upsampled to 192kHz, while 44.1 and 88.2kHz data are upsampled to 176.4kHz. The Compact Disc's 16-bit depth can be increased to 24 bits, the additional 8 bits filled with placeholder information. While this adds no new information, the conversions of the sample rate and bit depth transform the digital signal into a format that can be optimally converted into an analog signal by the DAC, says Bryston. The D/A conversion is done by a pair of Crystal CS4398 integrated-circuit chips, which feed discrete-component, class-A output amplifiers.

Knowing that the BDA-1's USB 1.1 input is limited to sample rates of 48kHz or lower, I used a Bel Canto USB Link 24/96 adapter (see John Atkinson's review in the May 2009 Stereophile, Vol.32 No.5) to connect my Lenovo X61 laptop's USB feed to one of the Bryston's S/PDIF inputs with audio data up to 96kHz sample rates. The BDA-1 is small enough that I could place it atop my BCD-1 CD player. I connected the BCD-1's S/PDIF output to the BDA-1's S/PDIF input via a single Wireworld Starlight coaxial cable. I ran both single-ended and balanced Bryston XLR interconnect cables from the BDA-1's output jacks to my Bryston BP26 preamplifier. I left in place the single-ended interconnects that ran from the BCD-1's analog output to the Bryston BP26, whose front-panel input switch could then switch between the BCD-1's analog output, the BDA-1's analog output via single-ended interconnects, and the BDA-1's analog output over balanced XLR interconnect, all sourced from the BCD-1's CD transport.

The BDA-1 functioned flawlessly while I had it in my system. Digital signals were decoded instantly when an input was selected. As on Bryston's BCD-1 CD player, the BDA-1's status light goes dark when the unit is turned on; in standby mode, it glows red.

The first hi-rez digital music tracks I played on my laptop was a 24-bit/88.2kHz WAV file from a Naim recording of the Chamber Soloists of the Royal Philharmonic Orchestra playing Mozart's Eine kleine Nachtmusik (from Naim Classical HD126). I also downloaded two files from a 24/88.2 file of Beethoven's Symphony 3, "Eroica," performed by Andrew Manze and the Helsingborg Symphony (from Harmonia Mundi HMU 807470); and all eleven 24/96 tracks of Chesky's Ultimate Demonstration Disc, Volume 2 (originally on SACD, Chesky SACD343). The BDA-1 processing these hi-rez tracks sounded light-years ahead of CD-sourced music I've heard in my listening room. The BDA-1 reproduced the music's warmth and fullness with none of the irritating edginess I've heard from earlier standalone DACs.

Bryston Ltd.
PO Box 2170, 677 Neal Drive
Peterborough, Ontario K9J 6X7
(800) 632-8217

Metalingus's picture

What is it like with oversampling off? Does it have a perfect response like a NOS DAC? If so this has the best of both worlds, inaudible distortion and good impulse.