DIY Transport and DAC
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DIY Transport and DAC |
After many years of my processing only being available to commercial customers, I decided to do a stripped-down version of the transport with excellent sound quality, so DIYers can experience a taste for themselves...
The Lightweight Transport
and Discrete DAC were demonstrated at meeting of audio enthusiasts in
London, and the DIY version became known as the "Starlight Project"
after a stellar Miles Davis performance of "Stella By Starlight"
through some impressive electrostatic speakers driven directly from
push-pull 300Bs.
The
result is a CD transport with a single optimised (for listening
pleasure) oversampling filter, and a fixed output rate of 176.4K, with
the possibility of connecting to either PCM1704 DACs or my Discrete DAC
designs.
The motherboard is an Intel D201GLY2. This is a low cost Mini-ITX motherboard which is fanless and provides more than adequate processing performance... the software benefits from SSE2 to perform its double precision floating point arithmetic, so the Core Solo is perfect.
Providing the user interface is a simple microcontroller with software developed by Richard Danielian (further information available here), which talks to the transport through a serial interface at the traditional 9600 baud, NE1 format... single characters are sent through to the transport, with strings sent back for status information. It can also be controlled through a regular terminal program and a laptop.
For the sound card, anything based on an Envy24 (ICE1724/VT1724) should work... this covers a lot of M-Audio and Terratec designs aimed at the semi-pro music and HT markets. To achieve 176.4K, a data line per channel is used.
The system requires at least a 256MB drive to boot from, and it has been found to be optimal to use an industrial grade solid state drive, either with an IDE interface, or CF supporting reliable UDMA with an IDE adaptor. The software is still licensed as per the Ti48, and is provided pre-loaded on a suitable disk.
For the optical drive, a Toshiba (pre Samsung) is recommended, as these have been found to remain quiet once they have buffered and started realtime speed digital audio extraction...
The pictures show Richard's own setup, which uses his PCM1704 based DAC with a valve output stage. The PCM1704 won't talk directly to the Envy24 as it requires right justified data, but fortunately Richard has come up with a schematic which works around that... :)
The data format is also slightly different (my Discrete DAC expects a complementary offset binary format (COB) while the 1704 works on 2s complement) which is a change that has to be done at the transport software side.
The schematic for the 18-bit Discrete DAC can be found on the Discrete DAC page.
The same signal processing ideas for the Lightweight apply to the DIY Transport, and a particular interest might be to have fast convolution support working, which would allow for speaker or room correction with suitable software to generate the filters.
Here's a picture
of Richard's finished box for his DIY PCT...
Here
is the outside view...
