DIY Digital conversion

[Tim Godfrey]

I have designed and built a circuit to take a coaxial SPDIF input and
generate buffered SPDIF and AES/EBU outputs. This circuit draws on the
CS8401 app notes, and the SPDIF article at
<http://www.hut.fi/Misc/Electronics/docs/audio/spdif.html>.

I used a DS8921 RS422 tranceiver chip rather than CMOS logic gates, because
the differential receiver section is designed for this application. It has
a small, controlled hysteresis zone, with a threshold of under 200mV
(typical 35mV). The threshold and hysteresis of a CMOS logic gate is
unspecified and can vary from unit to unit and manufacturer to
manufacturer. (also, I had some DS8921's on hand ;-)

My schematic is at <http://home.unicom.net/~tgodfrey/SPDIF_Buffer.PDF> if
you want to take a look.

Comments are welcome.

By the way, the reason I made this is because I'm connecting a digital
audio interface in my computer (SPDIF output) to a Tascam DA-30mKII DAT (on
the AES/EBU input since the SPDIF input goes to my CD player), and also to
a DACMAN at my mixer via SPDIF. I wanted full isolation between the outputs
to prevent ground loops.

Thanks,

Tim.

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