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Unbalancing digital output?

Postby vinyl_junkie » Sat Jan 19, 2013 6:54 pm

Quick question

Some devices only have digital outputs on XLR connectors.
In my case these can be switched to either output the AES/EBU digital standard or the "consumer" SPDIF standard.

Now I guess silly question but how can I wire this up to go into a RCA plug so I can plug it into a consumer type device which has the digital input only on RCA's?

I'm guessing the GND and Cold terminals will be both going to the sleeve and the Hot pin to the center pin on the RCA?
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Re: Unbalancing digital output?

Postby Hugh Robjohns » Sat Jan 19, 2013 7:07 pm

Most digital inputs and outputs are via tiny 'pulse transformers' which means they are 'floating'. So the signal is presented on pins 2 and 3 on the XLR and you just need to wire it to the pin and sleeve, respectively, of the RCA phono connector. Strictly speaking the two interface formats have different impedances (110 vs 75 ohms) but provided you are connecting one source directly to one destination over a shortish cable (a couple of metres maximum) it will work just fine.

H
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Re: Unbalancing digital output?

Postby ef37a » Sat Jan 19, 2013 10:53 pm

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Re: Unbalancing digital output?

Postby Goddard » Sun Jan 20, 2013 3:11 am

Hugh Robjohns wrote:Most digital inputs and outputs are via tiny 'pulse transformers' which means they are 'floating'. So the signal is presented on pins 2 and 3 on the XLR and you just need to wire it to the pin and sleeve, respectively, of the RCA phono connector. Strictly speaking the two interface formats have different impedances (110 vs 75 ohms) but provided you are connecting one source directly to one destination over a shortish cable (a couple of metres maximum) it will work just fine.

H

IME, the coax S/PDIF inputs on a lot of gear (esp. "consumer" and even "prosumer" devices) are not transformer-isolated (even if the same device also has a coax S/PDIF output which is itself galvanically isolated). This should not be a problem so long as the coax S/PDIF source output being connected to is itself isolated, and Hugh's advice is still valid even in such a case. But as a precaution, make the connections before powering up.

Why I prefer running S/PDIF (or AES/EBU) over TOSlink optical when possible...
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Re: Unbalancing digital output?

Postby Goddard » Sun Jan 20, 2013 3:16 am


Hey Dave, Midiman made a box for this job too (find 'em cheap nowadays):

http://m-audio.com/images/global/manuals/CO3_Manual.pdf

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Re: Unbalancing digital output?

Postby Hugh Robjohns » Sun Jan 20, 2013 12:49 pm

The midiman box is a powered format converter and is useful if you need to send an S/PDIF signal a long way via AES3, but the expense is unnecessary for a short-length connection in the back of a small equipment rack etc.

The Balan Dave linked to is a nice and proper way of dealing with S/PDIF to AES interfacing, but again is significantly more expensive than a simple 'bodeg cable' and -- in these examples, at least -- will need BNC-RCA adapter cables anyway (since the balan is actually designed to convert from AES3 (on balanced XLR) to AES3-id (on unbalanced BNC cable) formats.

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Re: Unbalancing digital output?

Postby vinyl_junkie » Sun Jan 20, 2013 1:05 pm

Many thanks for all the helpful replies
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