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I make it no secret that I prefer coaxial or USB inputs to Toslink inputs on digital-to-analog converters. In my opinion, these yield the best measured performance.
However we have to live with the digital output types that the device we want to use is equipped with. Even highly acclaimed set-top boxes including Apple TV only come with optical outputs.
But what if your DAC doesn’t have sufficient optical inputs to juggle your connectiviy needs or no Toslink inputs at all? I am going to show you two practical solutions to this common problem.
Let’s start with the first approach:
Optical to coaxial converter
A number of manufacturers are selling aftermarket devices that take your optical Toslink signal and convert it into coaxial SP/DIF. Boom! Job done. You basically need a standard optical SP/DIF cable that goes between the external converter box and your digital “source” device (e.g. Blueray player or set-top box). Only drawback is that the little converter box needs its own power supply which usually comes with the converter itself. And you have yet another dongle dangling off the back of your DAC. But this seems like a reasonable compromise and certainly better than having no optical inputs at all.
As far as sound quality, you needn’t worry. Optical receivers inside DACs do exactly the same as the external box which is converting optical impulses to electrical ones. Just that these are already built-in. There’s no lossy data conversion going on and certainly no D > A or A > D conversion process involved. Why would manufacturers spend extra money anway? ;)
You can buy a Monoprice Optical Toslink to Coaxial Converter on Amazon for less than 20 Euros (advertisement)
An added bonus of these types of converters is its flexibility. You are not limited to a particular input of your DAC.
You could easily make input 2,3 or 4 your “optical input”. And you can add as many of those boxes as you need. An external converter box also makes sense for digital-to-analog converters with a single coaxial input.
Retrofitting optical inputs
This is a more permanent solution and a good approach if you have some DIY electronic skills. You can buy dirt-cheap pre assembled boards straight from China for less than 10 Euros.
Check out http://www.diyinhk.com/shop/audio-kits/83-192k-optical-spdifreceiver.html.
It comes with everything except a 3.3V power supply. I believe they also sell those separately otherwise you need to hack into your DAC board and look for a 3.3V source somewhere on the PCB. You also need to do your homework and find out where you can connect the data lines. Because your DAC does not have provisions for the new input, you might have to knock out an existing SP/DIF input to make room for your optical receiver. The ugliest part though is to drill a hole into the back panel of your DAC. Since the optical receiver itself has a squared shape, it could become a messy job if you want the finished job to look halfway professional. Alternatively, you could install the little optical receiver inside an external box but you definitely want to keep the data lines short.