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RE: any plans for a DAC?

Posted by Doc B. (M) on May 28, 2009 at 14:48:32

In Reply to: any plans for a DAC? posted by hermanesque on May 28, 2009 at 13:10:00:

John Swenson and I have been working on something (well, John has been doing most of the work, I am mostly the orchestra conductor for the artists around here these days). The goal is to come up with a DAC that will be suitable for the influx of high res digital files that we feel will hit the market as music servers move in to replace CD players.

My initial desire was to have a 24/192 capable NOS R2R DAC, possibly integrated into a dedicated server. After looking at some more exotic options like custom laser trimmed temperature controlled resistor arrays it became clear that the most straightforward way to do this DAC and get the best sound we could was to use the PCM1704. Folks will note that this chip is spec'd as a 24/96 chip when used with the factory recommended 8X oversampling filter, but it is in fact capable of doing NOS 24/192.

About this time I started reading some ideas that John had posted and we got in touch. John has some very cool ideas for interfacing this chip with the rest of the circuit, involving the use of a FPGA and a custom transformer that will tie the 1704 to a tube output stage (which of course PJ and I will be involved in). He has some great knowledge of the potential pitfalls of filters and has come up with a nice scheme for optimizing that aspect of the design.

Though the initial idea was to use this in a dedicated server, the current state of server development and software development led us to instead come up with a freestanding DAC kit concept that can work with a lot of different soundcards and that way we can let the software guys worry about talking to those cards. I can't speak about interfaces in detail at the moment as we still need to assess which ones will let us do all of the things we would like the DAC to be able to do. TOSLINK (limited to 24/96) and coax S/PDIF inputs will be available for sure, which means AES/EBU as well. And quite possibly it will have a USB interface, though that is not yet firm. There's a few other things that John will be experimenting with, that I can't go into yet.

A great deal of effort will also be put into both the digital and the analog power supply design. This project is still in the relatively early development stages. John has one board powered and passing signal, so we have moved from the hand waving phase to the very exciting step of having something we can start to test. Results so far are very promising. I'd guess we are still a few months away from any kind of formal product announcement.

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