Improving Your DAC's Jitter Reduction

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Here is a simple change you can try on your DAC if it uses the Crystal CS8412 or CS8414 input receiver to lower the jitter filter cutoff frequency.
The input receiver is designed to lock very quickly to a wide range of input data rates. For this function, it uses an internal phase lock loop (PLL) with a cutoff frequency above the audio band and so there is not really any reduction in data correlated jitter from the transport and cable interface. The dynamics of this PLL is partly controlled by an external resistor and capacitor connected between pin 20 and ground. The values recommended by Crystal and used by most manufacturers are 1000 ohm/0.047uF for CS8412 and 470 ohm/0.068uF for CS8414.
The resistors can be reduced substantially or shorted and the capacitor can be increased to improve the jitter reduction up to the point where it becomes difficult to achieve a consistent lock. Some values to start with that shouldn't cause any problems are 100 ohm/2.2uF on the CS8412 or CS8414. Install pins in the PC board to allow experimenting and use quality parts (metal film resistors and plastic film capacitors). Alternately, you can leave the current parts in place and connect an additional network or capacitor alone from pin 20 to ground. Or leave the resistor and just increase the capacitor value. More advanced experimenters can even use a relay activated by a time delayed lock signal to control a filter with a much lower cutoff frequency. Have fun and report your findings.
Dave

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Topic - Improving Your DAC's Jitter Reduction - Dave Ingels 11:10:54 11/02/99 (2)

Re: Improving Your DAC's Jitter Reduction - Scott 07:53:03 11/04/99 (1)

Re: Improving Your DAC's Jitter Reduction - Dave Ingels 08:32:26 11/04/99 (0)

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