Sunday, 16 February 2014

El Cheapo Chinese USB Sound

The 99p USB soundcard arrived yesterday from China. My other USB soundcard, the one im running WSPR with, was from a UK seller and cost a whopping £1.49. So, are there any differences?

Oh, yes, indeed there are! The first difference, is that the plastic case 'feels' a bit more flimsy. Only a bit, and it has a few bits where the molding machine wasnt quite as clean and accurate as it should have been.

But the real obvious difference is internal. I had read up about this possibility with these cheap units, and its not in anyway a big problem for me, but if you bought one of these and happened not to be an engineer, it could cause you some grief. Take a look at the second photo. You can see, close to the two sockets, two pairs of solder pads. These are bridged by a PCB track. But what should be there, are the two DC blocking electrolytic coupling capacitors!

Without those capacitors, the audio lines have a DC bias on them. This might not be a problem for, say, an electret microphone, but its probably none too clever for your headphones or most other things you might connect, including in my case radios!

So it seems the difference in price is accounted for by the manufacturer saving a few pennies on a pair of electrolytics. This isnt a problem for me, as it was always my intention with this one to separate it from its case, and use it as a built in soundcard for a 'universal' digimode interface. I will be removing the connectors, wiring the soundcard PCB direct to the isolation transformers and level controls. The USB plug will also be removed and a panel mount USB socket added, along with line filtering. I will put suitable capacitors on at the same time.

I have connected this up to my laptop, and the drivers installed fine, and the computer sees it just fine. I will test the performance later.

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