This page intends to provide you with a birds-eye overview on the main building blocks of our DAC.
The design can be roughly partitioned into a digital part and an analogue part.
The spdif input signal of the digital source (e.g. a CD drive) must be converted to an analogue signal. The following topology has been chosen.
- Receiving the spdif-input stream (Tx + Receiver). The DAC accepts an spdif signal of a digital source (e.g. a CD drive). Tx is an input transformer to attenuate spurious common-mode currents which might run along the digital cable from the CD drive. The receiver (a Crystal CS8412) extracts a 44.1kHz clock signal and a 16 bit data signal from the spdif signal.
- Digital filtering (Dig. Filt). The digital filter converts the 44.1kHz 16-bit input signal into an 8x oversampled signal (352.8kHz, 20-bit, left and right seperate). This will make the analogue filtering section, which is needed after the da-conversion chip, easier to implement.
- Digital to analogue conversion (Dac). The digital-analog converter chips convert the oversampled signals from the digital filter into an analogue current.
- PLL+re-clocking (PLL Vcxo + Reclock). The clock signal generated from the input receiver is not stable enough to use as a clock signal for digital-analogue conversion (many high-end implementations still do!!!). A PLL is used to create a stable clock, and a reclocking stage is used to synchronize all these signals to this stable clock.
- Power supply (Supply Dig.). To minimize cross-talk effects between the digital and the analog circuitry, the digital circuitry has its own power supply.
The output of the DAC chip is a current source. To be able to connect the DAC to an amplifier, the current must be filtered, to get rid of the high-frequency sub-bands, converted to a voltage, and amplified to 2Vrms. This is performed as follows:
- Analogue Filter (Ana.Filt). An analog filter is needed to get rid of the high-frequency components in the output signal.
- Amplifier (Ampl). The amplifier is needed to bring the small voltage from the analog filter upto a level which is common for cinch outputs.
- Analogue power supply (Supply Ana.LowV, Supply Ana.HighV) A separate power supply and transformer is used for the 'analog' power supply pins of the DAC IC's. A third power supply is used for amplifier.
Copyright © 2001, Marc Heijligers and the DAC group - All rights reserved.