S/PDIF, was Re: 240volts and ground hum problems.

[Ingo Debus]

The Dark force of dance wrote:
> For the record S/PDIF can be transformer isolated but is not balanced. But
> from what I've seen there is not standard upon which sets down where the
> pulse transformer should be. Some devices only have a transformer on the
> input or output. Some have it on both and some have it on neither. My
> saving grace so far is that the digital audio has often been more or less
> paralleling the analogue audio so it hasn't been a big problem.

I just added a coaxial S/PDIF out to my Sony DTC-790 DAT recorder (has
optical out only, but optical and coax in). It was very simple: I just
connected the signal from one pin of the optical transmitter via a 390
ohms resistor to the output jack. I saw in an old Elrad project that
they did it the same way from the output of a 74HC04. Works good. But
I'm wondering if I should add anything? Protection zener diodes perhaps?
I don't quite see the need for a transformer, since the ground of the
coax input is connected to the DAT recorder's ground.
Why did Sony leave out this feature if it costs just one resistor and
one jack??


> But on the whole, devices with digital I/Os have some big advantages. I
> just wish the had an S/PDIF I/O option for the O1V. I'm guessing from
> memory that I could shove S/PDIF up it's AES/EBU I/O option but I'd like to
> get a definitive answer  on that before I spend all that money. Not that
> I've got the money to spend on it this year anyway so it's all a bit
> academic. But logic tells me that there are only a few differences in the
> subcodes and I think you can alter the way the O1V behaves in response to
> sub-codes.

I heard S/PDIF and AES/EBU can just be connected, but I never tried
myself.

Ingo