[sdiy] Isolating an external DAC from computer Soundcard

[Ingo Debus]

Am Sonntag, 16.05.04 um 18:22 Uhr schrieb Linium:

> I thought about an opto-coupler but so far i don't find a high speed 
> one able
> to support 24 mhz.
>

The "opto-couplers" normally used for SPDIF are these TOSLINK thingies. 
Put a transmitter on your soundcard, a receiver into your device, 
connect them with an optical cable  and you'll never have to worry 
about ground loop problems again. The TOSLINK receivers/transmitters 
have TTL inputs/outputs.

"Electrical" (coax) SPDIF is usually transformer coupled. Never done it 
myself, but I think these simple transformers can be self-made.

> Do you think that my trouble could mainly come from linking the 2 
> grounds
> (computer card and external supply) together ? And may be a simple
> counter-mesure would exist to somehow isolate grounds (caps) ?

If it's a ground loop problem (likely) the problem is that the two 
grounds are connected in another place, perhaps via Protective Earth. 
Almost every computer has its signal ground connected to Protective 
Earth.

Ingo