Sign in with
Sign up | Sign in
Your question

PC to audio gear problem with digital I/O

Last response: in Home Audio
Share
Anonymous
June 8, 2005 2:15:50 AM

Archived from groups: rec.audio.pro (More info?)

I have an RCA SPDIF audio output on my PC. So I made up a 12m cable of
75-ohm coax with RCA on one end and XLR on the other end (earth pin shorted
to neg pin) to hook it up to a Behringer DEQ2496. No signal registers on the
DEQ. If I use the same cable between my CD player and the DEQ, it works.

Any explanations please?

P.S. the PC to DEQ connection works with a 1m interconnect made from
balanced mic cable. So there is output at the PC's SPDIF, and the DEQ can
detect it.
Anonymous
June 8, 2005 2:15:51 AM

Archived from groups: rec.audio.pro (More info?)

nowater wrote:
> I have an RCA SPDIF audio output on my PC. So I made up a
12m cable of
> 75-ohm coax with RCA on one end and XLR on the other end
(earth pin
> shorted to neg pin) to hook it up to a Behringer DEQ2496.
No signal
> registers on the DEQ. If I use the same cable between my
CD player
> and the DEQ, it works.
>
> Any explanations please?

SPDIF involves a signal that is bipolar around ground, and
has a peak-to-peak amplitude of about 1 volt. Open-circuit,
you might see more like 2 volts peak-to-peak.

AES/EBU involves a TTL-compatible signal that is runs
between 0 volts and about 5 volts, again under load.

Put in a coupling capacitor and presume some overload
capacity on the part of the SP/DIF input and you can see how
an AES/EBU device can easily drive a SP/DIF input.

However, when you hook a SP/DIF *output* (no more than 2
volts, and no more than +1 volt peak) to a AES/EBU input
requiring a TTL-like input (3-5 volt swing above ground
required) and I think you can see the potential problem.

> P.S. the PC to DEQ connection works with a 1m interconnect
made from
> balanced mic cable. So there is output at the PC's SPDIF,
and the DEQ
> can detect it.

I think you got lucky. Are there any differences between the
1M cable and the 12M cable other than length?
Anonymous
June 8, 2005 2:34:20 AM

Archived from groups: rec.audio.pro (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:FLOdnYo9T774BDjfRVn-1w@comcast.com...
> nowater wrote:
> > P.S. the PC to DEQ connection works with a 1m interconnect
> made from
> > balanced mic cable. So there is output at the PC's SPDIF,
> and the DEQ
> > can detect it.
>
> I think you got lucky. Are there any differences between the
> 1M cable and the 12M cable other than length?

1M is balanced mic cable, 12M is 75-ohm coax. I saw on a newsgroup that
75-ohm is optimum for SPDIF.
Related resources
Anonymous
June 8, 2005 2:34:21 AM

Archived from groups: rec.audio.pro (More info?)

In article <42a59b2b$1_2@news.melbourne.pipenetworks.com> nowater@grantsellek.com writes:

> 1M is balanced mic cable, 12M is 75-ohm coax. I saw on a newsgroup that
> 75-ohm is optimum for SPDIF.

This is correct, but 12M might be a little too long given the cable
loss (unavoidable) and lower output voltage of S/PDIF compared to
AES/EBu. Generally 10 meters is considered the upper limit, but that's
greatly dependent on the output level of the source and the input
sensitivity of the receiver.

Can you move the DEQ closer to the computer?

You might have better results by using a matching transformer at the
computer end and switching to 110 ohm AES/EBU cable, but a transformer
is a relatively expensive item, and there's no guarantee that it will
work in this instance.



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
June 8, 2005 2:55:35 AM

Archived from groups: rec.audio.pro (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:FLOdnYo9T774BDjfRVn-1w@comcast.com...
> nowater wrote:
> > I have an RCA SPDIF audio output on my PC. So I made up a
> 12m cable of
> > 75-ohm coax with RCA on one end and XLR on the other end
> (earth pin
> > shorted to neg pin) to hook it up to a Behringer DEQ2496.
> No signal
> > registers on the DEQ. If I use the same cable between my
> CD player
> > and the DEQ, it works.
> >
> > Any explanations please?
>
> SPDIF involves a signal that is bipolar around ground, and
> has a peak-to-peak amplitude of about 1 volt. Open-circuit,
> you might see more like 2 volts peak-to-peak.
>
> AES/EBU involves a TTL-compatible signal that is runs
> between 0 volts and about 5 volts, again under load.
>
> Put in a coupling capacitor and presume some overload
> capacity on the part of the SP/DIF input and you can see how
> an AES/EBU device can easily drive a SP/DIF input.
>
> However, when you hook a SP/DIF *output* (no more than 2
> volts, and no more than +1 volt peak) to a AES/EBU input
> requiring a TTL-like input (3-5 volt swing above ground
> required) and I think you can see the potential problem.

The DEQ is switchable between AES/EBU and S/PDIF. The problem persists on
either setting.
June 8, 2005 2:55:36 AM

Archived from groups: rec.audio.pro (More info?)

On Tue, 7 Jun 2005 22:55:35 +0930, "nowater" <nowater@grantsellek.com>
wrote:


>The DEQ is switchable between AES/EBU and S/PDIF. The problem persists on
>either setting.

I think Mike has the right idea. For the distance you are working at,
the cable is not quite up to the task. SPDIF is just usually not
meant to run that far driven by most devices. You should be driving
your longer cable with AES/EBU and use the AES/EBU settings on your
input. While a matching transformer might do the trick or then again
maybe not, this $85 converter device by HOSA will definitely solve
your problem and you'll probably have a lot more reliable connection
in the future:

http://www.macmidimusic.com/prod.itml/icOid/1359

If that's too much, I've seen web sites how you can do this for $20 in
parts, but after I factor in my time, I'd rather just buy the
converter.

Julian

>
Anonymous
June 8, 2005 3:14:21 AM

Archived from groups: rec.audio.pro (More info?)

Julian wrote:
> ...While a matching transformer might do the trick or then again
> maybe not, this $85 converter device by HOSA will definitely solve
> your problem and you'll probably have a lot more reliable connection
> in the future:
>
> http://www.macmidimusic.com/prod.itml/icOid/1359
>
> If that's too much, I've seen web sites how you can do this for $20 in
> parts, but after I factor in my time, I'd rather just buy the
> converter.

How about this matching transformer for $20?
http://www.westlake-electronic.com/cgi-bin/store.php?se...

Is that a solution?
June 8, 2005 3:44:17 AM

Archived from groups: rec.audio.pro (More info?)

On 7 Jun 2005 23:14:21 -0700, "nowater" <nowater@supernerd.com.au>
wrote:

>How about this matching transformer for $20?
>http://www.westlake-electronic.com/cgi-bin/store.php?se...
>
>Is that a solution?

That's exactly what Mike suggested. In his words: "...there's no
guarantee that it will work in this instance..."

Someone correct me if I'm wrong, but I believe the BNC connector on
this transformer while unbalanced is actually designed for a higher
voltage than the RCA SPDIF output jacks you have. Basically it is AES
unbalanced device and you have SPDIF unbalanced. It might possibly
work here especially because you had some success with plugging your
CD player directly in, but there is no guarantee and even if it does
work your voltage is going to be marginally low and the whole system
will possibly be prone to failures.

That's why I suggested the other box. It takes what you have, RCA
SPDIF, and changes it to what you need, XLR AES, which can be run 100
meters or more.

Where do you live? I go to the main branch of West lake Electronics
here in Seattle all the time.

Julian
June 8, 2005 4:08:26 AM

Archived from groups: rec.audio.pro (More info?)

On Tue, 07 Jun 2005 23:44:17 -0700, Julian
<JulianPAdamsNo@SpamHotmail.Com> wrote:

>Someone correct me if I'm wrong, but I believe the BNC connector on
>this transformer while unbalanced is actually designed for a higher
>voltage than the RCA SPDIF output jacks you have. Basically it is AES
>unbalanced device and you have SPDIF unbalanced.

Duh! I just realized I overlooked something. The transformer you
linked to is designed for the opposite direction - adapting a device
with a balanced XLR OUT to a device with an unbalanced BNC IN. You
are going unbalanced RCA OUT to XLR IN.

Maybe if you bought two of them and a BNC cable and an XLR RCA
adaptor...and... you'd still have too low a voltage :-(

BTW they are saying this device allows you to run longer cables, but
they mean longer than AES XLR type 110 ohm cable which you can already
run much longer than you need. AES 110 ohm can run like up to maybe
100 m, but on the 75 ohm BNC type cable you can run maybe 300 m or
more. I don't remember the exact specs, but I do remember that is one
of the main usages for the 75 ohm cable, very long runs.

Just get the HOSA! It works both directions too.

Julian
Anonymous
June 8, 2005 3:28:55 PM

Archived from groups: rec.audio.pro (More info?)

In article <444da15u3t9f9e5rduiqqnijv6mt0o4rpp@4ax.com> JulianPAdamsNo@SpamHotmail.Com writes:

> That's exactly what Mike suggested. In his words: "...there's no
> guarantee that it will work in this instance..."
>
> Someone correct me if I'm wrong, but I believe the BNC connector on
> this transformer while unbalanced is actually designed for a higher
> voltage than the RCA SPDIF output jacks you have.

I didn't bother to paste together the long link (people should use
tinyurl.com for this) but I think you're right, at least in principle.
These adapters are meant to convert between unbalanced 75 ohm AES-3
(S/PDIF but at AES/EBU voltage level) and balanced 110 ohm AES/EBU.
The voltage ratio of a transformer is the square root of the impedance
ratio, so it only steps up the voltage by about 1.2. That might be
enough if the present level is just marginal, but it might not.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
!