Bottlehead Forum

Other Gear => Digital => Topic started by: rif on February 06, 2013, 08:09:23 AM

Title: switching between spdif inputs
Post by: rif on February 06, 2013, 08:09:23 AM

If I had a DAC with a single spdif (coax) input and I wanted to add another, could I use a simple switch (2 rca input, select 1 for the output)? I thought I could, but now I'm reading about galvanic, optical, and electronic isolation schemes. It's seems so simple yet so far beyond me, I'm almost afraid to ask the question.

-david

Title: Re: switching between spdif inputs
Post by: Grainger49 on February 06, 2013, 08:36:21 AM

Yes, but... the switch might mess up the receiving input impedance.  In digital signal transfer the input impedance can affect the transitions.  This is part of the little I know from slotted lines and transmission lines in school.

So I wouldn't do it. 

This question would be best answered by John Swenson.

Title: Re: switching between spdif inputs
Post by: rif on February 06, 2013, 02:46:17 PM

So I've been looking at some circuits and opening up some of my gear.

Someone let me know if this is right or wrong:

S/PDIF Coax inputs are transformer isolated
S/PDIF Coax outputs are not usually transformer isolated, but can be in some designs
TOSLINK/optical S/PDIF (once converted to electrical) isn't transformer isolated at all, send or receive.

So one transformer per coax input, switching to be done after transformer.

Can I use a simple switch at this point?

-david