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In Reply to: RE: IF you want a DAC to play normal "redbook" cds then you shouldn't buy the latest and greatest... posted by flood2 on April 16, 2014 at 15:02:11
All the DAC chips I am talking about required an external DF of some kind (PMD, DF1704 or similar). All I can tell you is that enough people were ultimately dissatisfied with the PMD100 to warrant replacement offers. To my knowledge no one wants to remove their DF1704s unless they are thinking of going NOS.
WHo knows?? Maybe you are right and the PMD100 is wonderful but misunderstood chip but the history suggests otherwise.
Follow Ups:
I'm not precious about the PMD100 at all. Leaving aside the DF from the equation, it has been my experience that the I-V conversion and output analogue filtering topology has a much more significant effect on the output sound...without changing anything on the digital side.
For example, I wouldn't use any other dielectric than polystyrene for my signal path caps, and I would implement a DC servo to avoid the need for NP electrolytics that many manufacturers pollute the sound with!
The other thing I think that is important is the op amp topology to implement the analogue filter.
If you look at the PCM63 and PCM67/69 application notes, they recommend a GIC configuration rather than the more common MFB topology. This is a much better topology I feel as it has the advantage that the passive component properties are what will dominate the sound quality. Next to PTFE, polystyrene is the next best thing in terms of low dielectric absorption and the result is a huge lift in realism and clarity (to me).
Secondly, this may explain why older DAC designs may sound better than new ones, simply because the designers followed the guidelines which just happened to have the better topology!
For what it's worth, I personally wouldn't choose to use a PMD100 now for any perceived benefit since the sample rate is limited to 55kHz and the DF1704 is a bit more versatile.
I'm actually working on a DAC design of my own now (and actually have a PMD100 from my X-DAC which now has a totally trashed PCB from all my reworks!), but I will implement the DF in software using a DSP. A separate DF IC is just too limiting!
"Beauty is Truth, Truth Beauty.." Keats
I don't disagree with you about the importance of the analog I/V conversion and filtering (or lack thereof); however, even the best implementations I have heard fall short of what I am hearing when a good ladder DAC is in place with a really good output stage.
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