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Making copper SPDIF in VIA chipset-based sound card

June 9th, 2017

When I got my VIA Tremor (Envy24DT) chipset based sound card from eBay, one of the firsts ideas was to convert existing optical (Toslink) SPDIF output into copper one. But at the beginning, I made few tweaks related to the power supply and output capacitors of this sound card.

Just before we start – one of the last tweaks

There are five SMD capacitors marked C3-C7 nearby the voltage regulator LM1117 as it is shown below:

Making copper SPDIF from VIA chipset-based sound card

Each of these caps is 0.1uF, which gives in total 0.5uF capacitance. I was not really confident that they would well dump any AC ripple. So, I de-soldered them to replace with higher quality Wima 0.1uF caps (via eBay) as you could see below

Ok, right now I will be able to sleep well 🙂

Back to the SPDIF copper output

First, you will need to unscrew the metal bracket. Then, you will have to de-solder the optical transmitter in order not to load the VIA SPDIF output with unnecessary load and use its current. You will need it later to drive your copper SPDIF input of the audio DAC (via eBay). However, these are not only needed changes.
Most of the sound cards produce TTL level SPDIF output. What does it mean in practice? It’s simple to high (reaching 5V or so on). So, we need to convert it. After some googling, I found very similar simple circuits like these which allow getting “right” SPDIF signal levels out of the sound card:

Making copper SPDIF from VIA chipset-based sound card

Basically, the capacitor is used to decouple the AC component and the signal goes through the voltage divider made out of two resistors. Lampizator recommends to use only the capacitor too for SPDIF output instead of cheap transformer. So, the circuit is really simple, let’s do it!

The pin for output of SPDIF signal from VIA chipset can be seen here. It’s the lowest from three pins of the optical transmitter as you can see here:

Making copper SPDIF from VIA chipset-based sound card

Once the de-coupling capacitor is in place, we can screw the RCA socket into the place of old optical socket and screw the bracket back. Later, solder other parts (missing resistors and RCA type socket) like this:
After all this, we got around 20Eur SPDIF output from your PC. It’s really not too bad.

Making copper SPDIF from VIA chipset-based sound card

Listening the music trough the SPDIF output

I connected a non-expensive ES9023 (aka SABRE) audio DAC (via eBay) to my just soldered copper SPDIF output. Well, the results were above the expectations. ES9023 audio DAC sounded simply better than integrated VIA VT1618 audio DAC chip 😉

Few remarks

The next day, I switched on my audio setup and … it did not produce the sound. After spending some time on debugging, it appeared that PC should be first booted without connecting anything to copper SPDIF. And only after it booted, the SPDIF output could connected to the audio DAC. Quite strange… Either that is caused by some static behavior or it is specific to this sound card HW. Still, I don’t know 🙁 But if that is not a real issue – everything else works well and you can connect an external audio DAC (via eBay) and enjoy the music 🙂