Maker Pro
Maker Pro

SPDIF to TTL

  • Thread starter Dirk Bruere at NeoPax
  • Start date
W

Winfield Hill

Jan 1, 1970
0
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.
 
G

Grant

Jan 1, 1970
0
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

M.Randelzhofer

Jan 1, 1970
0
Dirk Bruere at NeoPax said:
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
 
W

Winfield Hill

Jan 1, 1970
0
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.
 
W

Winfield Hill

Jan 1, 1970
0
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.
 

Similar threads

D
Replies
2
Views
756
Dirk Bruere at NeoPax
D
D
Replies
1
Views
839
Archimedes' Lever
A
D
Replies
4
Views
2K
JosephKK
J
Top