DAC1 - Digital / Analogue Converter
The B.M.C. DAC 1 is not only a digital-to-analog converter, but also serves as a preamplifier and the control center of a consistent B.M.C. chain.
Accurate timing separates the men from the boys in the world of digital audio. This is where Superlink comes in. In addition to standard SPDIF inputs, the DAC 1 offers B.M.C.'s proprietary Superlink connection between itself and the BDCD 2. Superlink is an uncompromising digital connection that employs four separate BNC cables, one per clock and one for the digital audio signal, with the master clock very near the digital/analog conversion.
The DAC 1's asynchronous high-resolution USB input generates the music data stream just in front of the D/A conversion. The DAC 1's high-precision master clock is right next to the D/A-converter and creates the ideal foundation for a perfect time-corrected digital signal that produces a more natural sound than other DACs.
On the analog side, the signal-current from the D/A converter is transmitted to the output voltage inside a distortion-free Current Injection input and Load-Effect Free circuit with an extremely short signal path. The result: no "digital" sound.
The DAC 1 becomes the center of a high-end audio system through its preamplifier function. This can be accomplished with a classical preamplifier section for variation of the output signal or, in a B.M.C. component chain, by leading the audio signal straight to the B.M.C. power amplifier. The volume level is set at the DAC 1, and transmitted through an optical connector to the power amplifier, where the gain is adjusted. Result: Perfect lossless volume control.
Although specifying this component as a “digital to analogue converter” is certainly correct in technical terms, we feel it is actually rather a true
B.M.C. = “Binary to Music Converter”
Computer-based Audio of the Highest Quality Using the New Asynchronous High-Resolution USB Input
Integrating a computer into the audio system is becoming increasingly important, and opens up audio systems to high-resolution digital audio. B.M.C.'s proprietary Superlink between CD players and DACs sets a benchmark in this regard. The USB input yields an even more advanced measure.
The music stream for standard USB transfers is generated in the computer, but its quality depends on internal computer clocks not optimized for audio. Fortunately, the USB protocol allows a solution: the so-called asynchronous mode.
In asynchronous mode, USB music streaming is not synchronized to the computer's internal clocks, but by an external device, as in the B.M.C. DAC 1. The possibility of external clocking gives the DAC 1's asynchronous high-resolution USB input the ability to deliver better sound. It enables the DAC 1 to receive digital audio data from the computer then clock the data using a high-precision device. In addition, the data stream is created directly in front of the actual digital/analog conversion. The circuit, more elaborate than a standard USB circuit, provides a consistent jitter-free data stream, sampling frequencies up to 384 khz, and resolutions up to 32 bit.
This makes it possible to transmit modern recording-studio standards via USB from the computer. Many recording studios and musicians are already providing high-resolution music files online. The DAC 1's asynchronous high-resolution USB input makes it possible to listen to high-resolution music as it's meant to be heard.
The DAC 1's high-resolution USB port reproduces the naturalness and flow of a purely analog playback source, while adding the operating convenience of computer audio and the depth of information available in high-resolution digital recordings.
B.M.C.'s exceptional SUPERLINK connection is ideal for transmitting digital audio signals, and an alternative to established SPDIF-compatible interfaces such as AES/EBU 110 Ohm, coaxial 75 Ohm, and the optical Toslink. Unlike SPDIF transmissions, SUPERLINK does not merge digital audio signals and different clocks into one single stream that must be decoded back into separate signals and clocks after the DAC receives it. SPDIF makes sense from a commercial point of view, but SUPERLINK is a solution without compromise. It requires four times as many connection cables but avoids all coding processes. SUPERLINK transmits left/right-clock, bit-clock, and digital music data from the CD transport to the DAC while the DAC generated master-clock is sent from the DAC1 to the CD transport. Four 75-Ohm BNC cables with matching impedance conduct the transmission. SUPERLINK results in a more intense link to the music, a wider and more realistic soundstage, more detail, and beautiful sonic colors.
Sample Rate Converter
Due to the approach of Superlink just the shortest signal path is available and thus the sample-rate-converter (alias SRC, or up-sampler) is not available.
For standard SPDIF inputs the SRC may deliver a better result whenever the source signal includes a noticeable amount of jitter. But due to its digital signal processing an SRC adds a certain coloration to the music signal.
All other options are available for any digital input. Two different digital filters are available with either “Flat” frequency response optimization or “Pulse” for best dynamic response and with minimized pre- and post ringing. The pulse filter has a soft treble roll off, but specifically avoids the unnatural pre-ringing. In spite of its filter's soft treble roll off, it is generally considered as more transparent sounding.
Furthermore there is a “Low” ( 32fs) and a “High” (128fs) oversampling rate available. Both options have their individual character and are suitable for decent sound tuning. “Low” has a more dynamic and detailed expression, while “High” is softer and smoother.
The digital signal performance is further optimized by a clock synchronization circuit right in front of the DAC-Chips. All digital signals are re-timed to the local master clock and thus the point of lowest jitter is at the DAC-Chip where the analogue music signal is made.
Two PCM 1792 DACs in Mono Mode
The D/A conversion is made by two 24-Bit / 192kHz TI/Burr-Brown PCM1792 chips with current output.
CI/LEF Analog Circuit
The output current is filtered and converted to an output voltage by discrete, fully balanced I/V converters, which operate feedback free. Thanks to the special “Current Injection” circuitry a maximum of sound quality is preserved, which is stabilised with the unmatched “LEF” driver circuit keeping all the sonic details.
Originally those circuits were designed to put focus on the sound quality and leave the measurement specifications second, but the present standard is on a level that leaves no need for such a choice: Both are at the highest level and the sound is in a class of its own.
DAC1 has a pre-amplifier module with a multi-functional volume control. A motor driven, remote-controllable potentiometer is acting as a position indicator using an A/D-converter and a volume value is calculated which is transmitted in two different ways:
- One set of 62 steps of digital potentiometer in a balanced configuration, buffered by a set of LEF output drivers, which can drive power amplifier inputs as well as headphones. Balanced XLR outputs are available.
- An optical interface for a DIGM (digital intelligent gain management) control, for a lossless volume control of B.M.C.'s power amplifiers.
The second option does not require a preamp as long as the source is a digital one, so the fixed output can be connected directly to the power amplifiers. This signal is not divided inside the power amplifier, but always used untouched and the volume is set by 66 different power amplifier gain settings in 1dB steps. The usage is therefore not any different from a traditional volume control, but the impact of DIGM is remarkable:
- A: There is no excess gain in the amplifiers, and the signal path can be very short.
- B: Reducing the volume also reduces noise and distortions unlike a traditional volume control.
- C: DIGM reduces the final speaker voltage and there is no more gain afterwards, so noise is kept low.
- D: There is neither any traditional nor digital potentiometer inside the signal path.
- E: DIGM switches precise metal-film resistors in parallel to the signal current and thus is a native part of the amplifier's I/V conversion.
The DAC1 power supply is equipped with a bold selection of parts. An O-Core transformer represents a very good combination of AC power filtering and low magnetic noise. 31 “Balanced-Current” capacitors sum up to about 70,000 μF of storage capacity which would be respectable even for a power amplifier. Those capacitors are second-to-none with respect to sonic performance. Due to their specific design, cleanness, precision, power-feeling and sonic colors are on an exciting performance level.
In front of each functional circuit group is extensive voltage stabilization that is just as stable as a voltage regulator but without feedback loop. At these points “Balanced-Current” capacitors again enhance the performance as well as induction free Polysterene capacitors.
These carefully selected solutions for multiple of technical details make it possible for this DAC to produce a musical experience that lets you forget there is actually a digital origin. The music you hear is opulent, rich in details and emotionally affecting.
The Sound of Nature