SPDIF to TTL

[Dirk Bruere at NeoPax]

There are a number of circuits on the Net to do this. For example:
http://sound.westhost.com/project85.htm

In Fig 5 should that IC be a 74HC04 as stated, or 74HCU04?

 

[Winfield Hill]

Dirk Bruere at NeoPax wrote...

There are a number of circuits on the Net to do this.
For example: http://sound.westhost.com/project85.htm

In Fig 5 should that IC be a 74HC04 as stated, or 74HCU04?

That's a simple AC signal to DC logic conversion,

.. | \
.. AC ---||---+---| >O--+----
.. | | / |
.. | |
.. '---/\/\---'

I'd say, yes, in the absence of any signal, an HCU04 gate
would do a better job of settling at 1/2 Vcc, and perhaps
do so with less class-A current, but in the absence of a
signal, who cares what happens? In practice, S/PDIF lines
have a continuous AC signal, so this simplified circuit's
feedback RC node should find the average of the incoming
data stream. Also, the continuous huge signal means the
gates won't have a class-A rail-rail current problem.

s/pdif data doesn't have a 50% duty cycle, which gives me
pause, but Andrew Kilpatrick, Randy McAnally and ESP =
Rod Elliott swear by it, so it must be adequate.

http://www.andrewkilpatrick.org/blog/?page_id=215
http://www.andrewkilpatrick.org/blog/wp-content/uploads/2008/07/spdif_circuits.gif

OTOH, you can get official s/pdif receiver connectors and
ICs for a few bucks, and that seems a bit more professional.

 

[Winfield Hill]

Winfield Hill wrote...

s/pdif data doesn't have a 50% duty cycle, which gives me
pause, but Andrew Kilpatrick, Randy McAnally and ESP =
Rod Elliott swear by it, so it must be adequate.

Check that, s/pdif's biphase mark code is more than
close enough to a 50% average for good RC coupling.
http://en.wikipedia.org/wiki/Biphase_mark_code

 

[Grant]

Dirk Bruere at NeoPax wrote...

That's a simple AC signal to DC logic conversion,

. | \
. AC ---||---+---| >O--+----
. | | / |
. | |
. '---/\/\---'

I'd say, yes, in the absence of any signal, an HCU04 gate
would do a better job of settling at 1/2 Vcc, and perhaps
do so with less class-A current, but in the absence of a
signal, who cares what happens? In practice, S/PDIF lines
have a continuous AC signal, so this simplified circuit's
feedback RC node should find the average of the incoming
data stream. Also, the continuous huge signal means the
gates won't have a class-A rail-rail current problem.

s/pdif data doesn't have a 50% duty cycle,

Averages 50% in the longer term, that's why it's an AC coupled signal.

which gives me
pause, but Andrew Kilpatrick, Randy McAnally and ESP =
Rod Elliott swear by it, so it must be adequate.

http://www.andrewkilpatrick.org/blog/?page_id=215
http://www.andrewkilpatrick.org/blog/wp-content/uploads/2008/07/spdif_circuits.gif

OTOH, you can get official s/pdif receiver connectors and
ICs for a few bucks, and that seems a bit more professional.

Yes, but there's more to life than doing everything efficiently

Grant.

 

[M.Randelzhofer]

There are a number of circuits on the Net to do this. For example:
http://sound.westhost.com/project85.htm

In Fig 5 should that IC be a 74HC04 as stated, or 74HCU04?


--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.blogtalkradio.com/onetribe - Occult Talk Show

In the following schematics page 17 upper left corner, you see a working
solution (I have the eval board, its working nicely in coax SPDIF mode).

http://focus.ti.com/lit/an/slea035a/slea035a.pdf

MIKE

--
www.oho-elektronik.de
OHO-Elektronik
Michael Randelzhofer
FPGA und CPLD Mini Module
Klein aber oho !
Kontakt:
Tel: 08131 339230
Usst.ID: DE130097310

 

[Winfield Hill]

M.Randelzhofer wrote...

"Dirk Bruere at NeoPax" asked...

In the following schematics page 17 upper left corner, you see a working
solution (I have the eval board, its working nicely in coax SPDIF mode).
http://focus.ti.com/lit/an/slea035a/slea035a.pdf

MIKE

It's interesting that TI picks an 'U04. An 74LVC2GU04
to be exact. They do use this simple ac-coupled-circuit
in a PurePath Digital reference design for their rather
sophisticated custom silicon for high-performance audio.

 

[Winfield Hill]

Jim Thompson wrote...

'U04' Variants have been used like this "forever". Some
loonies have even been known to use them as amplifiers

Right, I'm well aware of that. Old stuff, dating back to
the 60s when I started using cmos, or COS/MOS as RCA called
it back then. But the question was about the viability of
non-U types for this, do you have an opinion about that?
Not what's naturally best, but whether it'll work OK.