DACs

Bryston BDA-1 Digital to Analog Converter and Halide Design USB to SPDIF Bridge

ARTICLE INDEX

Design

Bryston is a Canadian company known for decades as a solid-state amplifier manufacturer offering a 20-year warranty on its amps. Bryston builds more than just amplifiers, offering a full range of amplifiers, preamplifiers and digital sources. The digital components get merely a 5-year warranty. The $2,150 BDA-1 has been in production for a couple of years, and is still a state of the art DAC. It is based on the Crystal Semiconductor CS-4398 24 bit 192 kHz DAC chips. This is Crystal's best audio DAC and is widely regarded as one of the best DACs available. A Burr Brown SRC4392 sample rate converter pads 16 bit signals to 24 bit, and upsamples to 192 kHz for 32 kHz, 48 kHz and 96 kHz inputs, and to 176.4 kHz for 44.1 kHz and 88.2 kHz signals. This type of upconversion, converting to an integer multiple of the input signal, Bryson calls "synchronous," although the sample rate converter still reclocks the input signal. Precision crystal oscillators running at 128x the maximum sample rates (one for 192 kHz and another for 176.4 kHz) are used to clock the sample rate converter. The loop bandwidth of the reclocking phase locked loop is 10 Hz, which should reject all jitter in the audio band. A button on the front panel allows the upsampling feature to be defeated if desired and feed the input signal directly to the CS-4398.

The BDA-1 has a vast array of inputs: 2 RCA, 2 BNC, 1 AES-EBU, 2 optical Toslink and one USB. The RCA, BNC and AES-EBU digital inputs have matching transformers to ensure the proper impedance (75 ohms for the RCA and BNC inputs, 110 ohms for the AES-EBU inputs). A Burr Brown PCM2707 chip, with a 48 kHz maximum sample rate, provides the USB input. There's even a digital processor loop available. Front panel pushbuttons select digital inputs and LEDs above each pushbutton show which input is selected. An array of additional LEDs show the input sample rate and lock status. The LED above the upsample switch changes color based on upsampling to 192 kHz or 176.4 kHz. The only thing the front panel of the BDA-1 doesn't tell you is the bit depth of the input signal.

The BDA-1's analog outputs are entirely discrete (no op-amps), and are fully balanced. There are 4 complete Class-A output stages, each fed by one output of the two Crystal CS-4398 DACs, making the entire analog chain balanced from DAC to output. Both single ended RCA and balanced XLR outputs are provided, with the single ended outputs derived by summing the balanced analog output legs after the output stages.

The majority of the BDA-1's circuitry is on a single circuit board at the rear of the case. This board takes up the full width of the case, but only about ½ the depth. The board contains the power supply, digital circuitry and the 4 discreet output chains. A second small board right behind the front panel contains all the switches and LEDs. A flex circuit connects the two boards across an expanse of empty case. The case could have been made half as deep, but that would have resulted in pretty funny looking proportions. I assume Bryston made the conscious decision to make the case larger than needed for aesthetic reasons.