SPDIF: Digital-Analog Converter

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SPDIF: Digital-Analog Converter

Power Supply

A basic regulator circuit of 5 volt with dual output for digital as well as analog components is the required power supply. Ferrite bead of up to 40 MHz may be incorporated for reducing electromagnetic induction (EMI) and noise but the circuit can also work without it. EMI can be further reduced by use of copper ground plane.

Minimum Noise

For minimal output noise, it is essential to separate ground returns from digital and analog sections. It is recommended to use a low noise regulator because of low PSRR of the DAC’s class-A output. Regulators other than the standard 7805 may provide better results.

D/A Converter

Its two main components are the Receiver and the DAC. SPDIF decoder CS8414 has an in-built balanced RS422 Receiver compatible with both TTL and COAX. This SPDIF decoder recovers the stereo’s sample rate and connects to DACs directly using 3-4 pins. No micro-controller is required for this. The most used DAC is an 8-pin crystal CS4334. Its 128-512x over-sampling permits use at the output of first order simple low-pass filters. Output filtering helps to reduce noise further but is not required if internal analog filters and switched-capacitor DAC are used. This versatile DAC supports up to 24 bit and 96 kHz audio. This DAC can also be easily connected to the CS8414 receiver. “Pops” should be avoided at the time of activating the relays by keeping output at ground potential. Increasing resistors if wanted is possible but that would not be effective. DACs other than CS4334 can also be used to get up to 120 dB S/N and dynamic range. The maximum output for CS4334 is 1.2v RMS and this DAC with acceptable noise level (compared to majority DIY amplifiers) is recommended for starters. For best performance at high frequency, 100 nF ceramic-type bypass caps should be used on both ICs from A/D supplies to ground.

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SPDIF: Digital-Analog Converter