The better the transport, and the less the DAC has to worry about jitter, the better the DAC can do its job. They are both important ... but if I was upgrading one at a time, I would do the DAC first.
9 responses Add your response
Hi Tfee, the DAC is important, but the transport is equally important. The actual DAC chips in that Pioneer unit are good...the problems are due to the cheap parts and crappy implementation. If the DAC or transport you replace it with is not better in those areas, the sound will not improve much. People like Ric Schultz (from EVS...tweakaudio.com) modify those players. They make changes to many of the half-assed aspects of the transport, DAC, power supply, circuitry, etc. and turn them into completely different sounding players (with the exact same features).
As far as the tranport goes...if it's not good, it may turn a 0 into a 1, or vice versa, and I imagine jitter does the same thing. THe better the transport, the more 1's and 0's it will read correctly.
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.
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.