Its all in the DAC?

As a former industry expert on jitter in high-speed digital telecommunication systems, I always get sucked into these type of questions.... ;-)

It's key to understand that jitter on the 1/0 signal from the transport does not end when it hits the DAC, despite buffering. The clock that times the bits OUT from the DAC is derived from the input clock. The DAC represents a filter. Filtering jitter is not easy and it is never perfect. Jitter = distortion on the analog signal (discernable or not).

I have a 45A, even stock it never sounded "grainy," but it
did improve with some better parts in the power supply,
replacement of the cheap coupling caps, IEC connector for
a better PC, damping and decent ICs. Others(on the yahoo tact users group) report improvements using ERS sheets placed around the power supply and on the DAC.

Also, be sure to switch off the video section, when listening to CDs, DVD-As and SACDs.

Murphthelab, it's interesting what you're saying, could you give some more detailed explanation? Especially what happening when you have an external DAC, which usually doesn't have a dedicated clock sync. line from a transport.

It would seem to me that a DAC has two choices:

1) Use a PLL and a divider to get the DAC clocking signal from the incoming digital datastream.

2) Buffer the incoming data into memory and clock it out to the DACs using its own internal clock that is not related to that of the transport. A large buffer would be required for this to ensure that it never runs empty if there is a slight offset between the clocks in the transport and the DAC.

In situation 1, which is the majority of DACs, the quality of the transport clock could have a profound effect on the sound quality produced by the DAC. In situation 2 I would expect the transport to have a much lesser effect on the sound quality, unless it was so lousy as to cause the DAC to receive bit errors.

The key is that to most DACs the SPDIF or AES signals are much more than 1s and 0s ... they are really an analog signal that must be sampled (to recover the data) and tracked (to recover the timing). The quality of this signal is rarely so poor as to cause bit errors, but can be poor enough to ruin the clock that drives the DAC.

Seandtaylor99 is right on the mark. In category 2, the Genesis Digital Lens is an example procuct (which I use). In this specific example, the box has some intelligence and measures the average difference between the transport clock and the Genesis clock (temperature controlled crystal). This way it can set the necessary buffering level without undo buffer delay.