Digital patchbay

[Magnus Danielson]

From: mark verbos <a0284520 at addcom.de>
Subject: Re: Digital patchbay
Date: Wed, 25 Oct 2000 01:11:11 +0200

> 
> 
> Martin Czech wrote:
> 
> > I think max. F is  3 MHz.  Even CDxxxx muxers should handle that, may
> > be not at 5V.  A muxer will allways weaken the signal drive, so perhaps
> > a bus structure with tristate drivers is better.  All z but one, which
> > is the talker.
> >
> > Should be not critical layout, if the pcb lines get long, you'll have to
> > terminate the ends, groundplane recommended.
> >
> > AES/EBU has unfortunately a different format than SPDIFF.  Simple hardware
> > won't do in this case.
> 
> I did a factory designed mod to a Z systems digital patchbay that converted
> some of the channels form AES/EBU to SPDIF and all that was involved was 2
> resisters on each channel. I think all the mod did was change the gain of the
> op amp stage on the in and the out.
> 
> Z systems themselves faxed me the specs so I have to assume it is a proper
> change.

The AES/EBU and S/P-DIF are closely related. What sticks out is
* AES/EBU has an impedance of 600 Ohm, S/P-DIF has an impedance of 75 Ohm
* AES/EBU runs at +6 dBm where as S/P-DIF runs at 0.775 V (0 dBm)
* AES/EBU is usually run on XLR, S/P-DIF on RCA
* They have diffrent subcode formats

If anything of the above is incorrect, please forgive me, this is from
my memory and it is quite some time since I last dug deeply into the
innards of these.

They do share frame format, coding etc. If you only want to
interexchange the sound, then impedance, signal and contact adaption
is required. It's ugly but it kind of works.

Cheers,
Magnus