Cheap USB to BNC adapter for Mac & Windows

[sburrell]

Hi,

I'll admit to being a little embarrassed that I always seem to be asking for advice here, and never really giving back - but here's my chance to make up for it! :)

I'm after a cheap USB to SPDIF for my Mac Pro. Its main purpose is to allow me to connect my Mac Pro to a BNC input on my Cambridge Audio DACmagic mk3 and thereby forego the need to keep moving my optical cable between my (Windows-only) PCIe sound card (when playing games in Boot Camp) and the built-in optical socket on the Mac (which I've read is really quite poor, in audiophile terms).

I'm looking to spend no more than £30 including P&P, and I'd rather the item be sourced in the UK, but Hong Kong is OK so long as the customs fees won't mean I breach £30. Also, it has to have a BNC output, and it must be compatible with both OS X and Windows 7. All my music is 44.1/16-bit, and the DACmagic only goes to 48kHz, so I don't need anything with 24-bit/96kHz or what-have-you (though, obviously, if it's in budget…).

In return for advice on this, I'll post a comprehensive review. So, if there's something you noticed on the Web but didn't want to spend the moolah on right now, maybe I could be your guinea pig (within reason, of course;)) From what I've read about the Mac Pro's optical out, I'd be hard pushed to make things worse :(

Deal? :eyebrows:

PS: I did find a couple of pages a week or so ago detailing some devices for my price range, but Darn it all if I can't find them now! :steam:

[PaulStewart]

Just a point here, the optical output on the Macs do not have any problems with quality provided a good fibre cable is used. By that I mean one that is phase coherent and will not cause errors that make the error correction on the DAC work overtime. Real glass medical grade laser fibre is best in my opinion. Good mechanical quality connectors help here too. In my experience this is way better quality than cheap USB to SPIDIF. Also there is a lot of RFI in most computer environments, unlike cables, fibre won't transmit this to your DAC.

Just my thoughts on the matter

[sburrell]

The way I understand it is that the optical outputs on Macs are particularly prone to jitter. Refs here:

Computer Audiophile thread (http://www.computeraudiophile.com/content/Advice-integrating-DAC-Mac-Pro-iTunes-listening-setup#comment-20189)

Apple Discussions thread (https://discussions.apple.com/message/8186141#8186141)

Those are just from a quick search on DuckDuckGo. There were several links to opinions of generic motherboard-based optical outs that mention poor jitter too.

Another thing is that my DAC is, according to the designer himself (John Westlake) already very poor when it comes to jitter:


Unfortunately, the designs biggest weakness is the TDA1315 – the SPDIF input receiver. The TDA1315 has very poor jitter performance – despite claims otherwise from Philips[…]
(Dacmagic Mods - diyAudio (http://www.diyaudio.com/forums/digital-line-level/40594-dacmagic-mods.html))

I was hoping, by getting a USB to BNC converter, to kill two birds with one stone (or, at least, mildly concuss them).

[PaulStewart]

To be honest the really cheap ones are not that good and I feel that a lot of the jitter problems are down to fibre quality. But that said there is an adapter called a sound piper which you can get from HK on eBay which does the job. I used it recentley between an Acer PC and a prototype of a DAC Tannoy were developing years ago and it worked OK.

Hope this helps

[Stratmangler]

Just a point here, the optical output on the Macs do not have any problems with quality provided a good fibre cable is used. By that I mean one that is phase coherent and will not cause errors that make the error correction on the DAC work overtime. Real glass medical grade laser fibre is best in my opinion. Good mechanical quality connectors help here too. In my experience this is way better quality than cheap USB to SPIDIF. Also there is a lot of RFI in most computer environments, unlike cables, fibre won't transmit this to your DAC.

Just my thoughts on the matter

Phase coherent optical fibre?
:mental::mental::mental::mental::mental::mental:

[PaulStewart]

Phase coherent optical fibre?
:mental::mental::mental::mental::mental::mental:


Optical fibres are like any other form of optical device, such as camera lenses, subject to aberrations, refractions and internal reflections. *In better designed optical devices, these are controlled. *In poorly designed and constructed devices, they are not. *That is why a complex lens, with lens coating, internal flocking etc will produce a better image than one that is not so treated, the lack of this treatment, can, depending on the design, lead to anything from a lowering of contrast (reduction in definition) to ghost imaging. *In the case of an optical signal passed down fibre optic, a less well designed cable, and normally these will be of the cheap plastic variety, produces a large number of these anomalies. *This can lead to a literal ghosting of the bit word that is being sent at the time. *The result of this lack of phase coherence in the case of an audio signal means that the error correction in the DAC will have to work overtime and this will cause a "graining" of the perceived sound or worse. *A higher quality, well designed, cohesive fibre, normally glass, will produce less of these aberrations, in the same way as a properly constructed lens will work better than a single element of pressed plastic.

As you seem to think this approach is "mental", I should point out to you that knowledge of this is in no way new. *In the very late 60s when fibre optic was a new product, the American connector company AMP, who have been amongst the leaders of this technology since its inception, had a report that some optical fibres were giving problems in AMP's implementation of them in the French Air Force's version of the Force Du Frappe, the French airborne nuclear deterrent. *So these problems and their resolution are by no means new.

But there is a simple experiment to be done here, which I have demonstrated many times. *Take a high quality optical fibre, and a cheap as chips one, combine this with a DAC that gives you a read out of errors, swap the cables around and read the numbers. *I'm sure you will be able to manage that.

[sburrell]

I've decided to go with the FanMusic 6011 USB to SPDIF (RCA), but I'm still awaiting a response from the seller on eBay as to whether it's compatible with OS X. It's received praise from at least 3 owners here on AoS.

[PaulStewart]

Hu Simon,

The Fan Music is the same device as the Sound Piper, it should have no problems with osx and mac as it is just converting a data stream coming up the wire.

[sburrell]

Hey Paul,

Do you mean it's _the exact same_ device, just under a different name, or that it's a device that performs the exact same duties?

Either way, if I don't get confirmation from the seller that it works on OS X, and then buy it, and it doesn't work, I've got no recourse for a refund.

They're taking their blessed time - I emailed them several days ago now, close to a week. They passed the query upstream to the supplier, and I guess that's where the delay is. :(

[PaulStewart]

Hi Simon,

Yes same device different name. I still think something like a good Mark Grant optical will sound better

Best of luck

[sburrell]

Paul,

The cable may sound better, but please don't be offended if I draw your attention to what I said in my original post:


[The USB-to-BNC adapter's] main purpose is to allow me to connect my Mac Pro to a BNC input on my Cambridge Audio DACmagic mk3 and thereby forego the need to keep moving my optical cable between my (Windows-only) PCIe sound card (when playing games in Boot Camp) and the built-in optical socket on the Mac (which I've read is really quite poor, in audiophile terms).

On another note: I'm _still_ waiting for a response from the eBay seller regarding confirming compatibility with OS X - they in turn are still waiting for a reply from their supplier.

[Spur07]

This wont really affect your requirements Simon, but just to say I've compared a few spdif converters (the best of which was a Trends Audio) against the toslink output on my G5 tower and to my ears could hear no difference. I suspect to get significant improvement one would have to invest in something like a jkeny modded hiface.

[greygoose]

Hi, jkenny modded hiface is very ood interface and he now has an optional power supply upgrade unit to choose from.
Well worth a look.

[sburrell]

Paul wrote:

I've compared a few spdif converters […] against the toslink output on my G5 tower and to my ears could hear no difference.
I actually don't really have a problem with mine either, but the reports I'd read that they may be pretty poor just added further weight behind my desire to take advantage of two inputs on my DAC simultaneously. :) If the FanMusic sellers ever actually confirm it works with OS X, I can do a side-by-side and report on it here.

Colum wrote:

jkenny modded hiface is very ood interface and he now has an optional power supply upgrade unit to choose from.
I've heard good things about jkenny's mods, but unfortunately it's _well_ out of budget, costing more than 3 times the DAC itself. Ta though :)