Freitag, 11. März 2016

Splitters Suck - Adventures with Optical Audio, Part III

This is part three of a multi-part series, click here to read part one or here to read part two.

After I upgraded my PC subwoofer to optical audio input, I still had a problem: My sound card has only one Toslink output. But there is remedy! Toslink splitters! Hooray!

Those things have one input and two outputs, and entirely optical (passive). However they have a major flaw: They do not work! The plug conncetions and the prism have really bad optical characteristics and too much light is absorbed. At first, I thought the fibers were to bad, but I tried short (1m) high quality cables and experienced the same problem. Even cleaning the connectors didn't make it better, I figured out that one of the outputs was stronger than the other, it barely worked, the other one didn't work at all. A piece of junk.
You can buy active splitters, but the cheapest I found were around 50 euros, way too much money. I flirted with idea of building my own optical splitter, that would mean another box that needs power and an AC adapter though.
A lot simpler is upgrading the sound card to two optical outputs! I had still some Toslink emitters around, and I didn't really need the optical input of the sound card, so why not switch an emitter for another sender? The modification is quite simple: Just desolder the receiver, hot glue the emitter at the same place upside down (you cannot use the same pins!) and wire it parallel to the existing emitter. Just an aditional 100 nF capacitor and an 8.2 k resistor is needed (according to the datasheet i found).

Quite simple, but effective. Working like a charm.
- Marv

Donnerstag, 10. März 2016

Adding S/PDIF to Analog Hardware - Adventures with Optical Audio, Part II

This is part two of a multi-part series, click here to read part one.
The solution I presented last time was working pretty well for a few years. Someday, I upgraded my PC with a Radeon 7770 graphics card. Graphics were great, the sound horrible. - The sound? What does that have to do with a new graphics card, you might ask. Well, unfortunately, either due to noise on the power/signal lines on the main board or due to electromagnetic fields, each time the graphics card processes a frame, I heard a horrible ticking on my speakers. The rate and volume changed with the framerate and the complexity of the tasks. The noise however wasn't present on the digital outputs, only the 3.5 mm jack was affected. So why not upgrade the PC speakers to toslink?

No sooner said than done! I opened up the subwoofer and looked for a nice place where I could fit in another digital to analog converter, which I had to slightly modify:
I didn't want to use the RCA jacks since these need a lot of space. A convienient connector was already present to connect the analog input PCB to the main amplifier board, I just the same one on the bottom of the converter to be able to just switch a single plug:

Since the space on the back plate is really limited, I had to mount the converter flat on the sheet metal. Therefore, the optical input had to be mounted upright:

The last thing to do, was to make a rectangular hole in the plate. I predrilled with 3 mm, then drilled an 8 mm round hole. With a file I made the hole rectangualar:

And finally, lots of hot glue to mount it securely:

And it works! Ok, to be honest, these modifications wer nothing special, but sometimes the simple way is enough. There is one problem though - my sound card has only one optical output... But that's a story for next time.
- Marv