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Old 10th December 2010, 08:53 PM   #1
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Default DAC with digital (BNC) output

Good evening
I'm having a few problems configuring my system and wondered if anyone could help
I've recently purchased a Bryston SP1.7 receiver, which, becuase it's the pro model has a BNC input rather than optical via toslink.
I am just researching a DAC to feed my squeezebox signal into the by passed analogue inputs of the Bryston, but completely forgot that if I want to hook up a 5.1 source (such as a Humax digital box) with only optical outputs, I would be a bit stuck.
I've seen that you can buy optical to coaxial converters (no idea how damaging they are to the digital signal, but I wondered if there were any DACs which I could use with my squeezebox but which could also feed a digital signal to the Bryston via BNC
Can anyone help?
Steve
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Old 10th December 2010, 09:35 PM   #2
qusp is offline qusp  Australia
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you dont want a DAC, you want an audio interface or transport. something like an RME HDSP9652 PCIE card perhaps, or the RME fireface 400 (both of these have 5.1 pass through). cheaper units are available, but this one is pretty nice and will run via firewire from the computer, but also standalone with your squeezebox. you could also get a hiface USB to BNC.
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Old 11th December 2010, 01:54 AM   #3
alexcp is offline alexcp  United States
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Or you can use an RCA SPDIF output (or a TOSLINK to SPDIF converter) and a $1 RCA to BNC adapter. I know that connecting something so cheap to a Bryston may sound un-cool, but SPDIF interface is very much the same and generally compatible across BNC and RCA.
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Old 11th December 2010, 02:46 AM   #4
qusp is offline qusp  Australia
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well not really, it will work, but RCA coax and BNC coax are 2 entirely different things; one maintains the standard (BNC) and the other doesnt
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Old 11th December 2010, 03:00 AM   #5
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Well, not entirely different - otherwise it wouldn't work at all! The connector is different; BNC has higher signal level, but the level of RCA is within the acceptable range for BNC; BNC is normally 24-bit while for RCA 24-bit is optional and 20-bit is standard; and BNC has no built-in copy protection. Nothing on this list is critical for a system that currently uses TOSLINK for multichannel audio.
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Old 11th December 2010, 07:59 AM   #6
qusp is offline qusp  Australia
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I fail to see any relevance of RCA being 24bit or 20 bit, its a matter of not being possible to maintain the 75ohms standard. spdif 'works' on 2 wires, or a minijack, doesnt mean it does the job even close to spec. RCA or BNC with built in copy protection??....what? no connector type can possibly have built in copy protection its a completely passive device
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Old 11th December 2010, 09:31 AM   #7
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Thanks for the replies.
The PC is no where near my listening area anymore, so I'm not sure that the first options would be of any use.
As you will probably tell from this next statement, I'm definitely not an expert in this at all.
From what I've read, I thought that BNC formed part of the AES standard rather than the SPDIF path and that a BNC connection allows for a slightly better signal path than SPDIF coaxial or optical.

I guess I was hoping that there might be a DAC with digitial pass through function, which might preserve the digital signal and enable me to use the BNC connector.

The back of the Bryston has several coaxial connectors and so if I can't find a high quality connection path, am I best to simply use an optical to coaxial converter?

Or am I missing the point entirely.

I'm not sure what DACs are in the Bryston, but do you still think I'd see a benefit placing a DAC between the SB and pre amp for stereo listening?

Cheers

Steve
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Old 11th December 2010, 02:08 PM   #8
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Steve, you are right: BNC connectors are as per AES/EBU. SPDIF is a consumer version of AES/EBU. The differences I was referring to above are between the standards, not connectors. The two standards are more or less compatible electrically; you plug AES/EBU device into SPDIF, and it will work.

qusp makes a good point saying that a proper BNC connector in principle should allow better impedance matching and better quality. For the same reason, a BNC-to-BNC cable preserves the signal over much longer distance than an RCA-to-RCA. However, SPDIF is extensively used in consumer audio products of all prices ranges that get excellent reviews. You don't really need anything more for connecting a HUMAX box to a receiver. My thinking was that if you want a good DAC with digital passthrough, allowing yourself to choose from those with SPDIF output would give you a much wider selection.

By the way, TOSLINK is identical to SPDIF but uses plastic optical fiber instead of 75 ohm coaxial cable. Some people believe TOSLINK introduces more jitter compared to the coaxial cable. A good summary of the differences between AES/EBU, SPDIF and TOSLINK can be found in wikipedia.

Last edited by alexcp; 11th December 2010 at 02:17 PM.
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Old 12th December 2010, 07:10 AM   #9
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Hi Alex
Thanks very much for the reply and for providing clarity.
I was trying to find a DAC with digital outputs yesterday and the only one I've discovered so far is the Cambridge Audio DAC magic. Are there any other contenders, or even DIY versions?
Steve
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Old 12th December 2010, 12:49 PM   #10
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Quote:
Originally Posted by vetinry View Post
Hi Alex
I was trying to find a DAC with digital outputs yesterday and the only one I've discovered so far is the Cambridge Audio DAC magic... Steve
Those are INPUTS, because that's where your audio singnal enters the DAC.
Outputs are the analog ones.
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