My hassles with getting the new shack PC set up and working continue. I lost the configurations for KComm and Fldigi, including all my macro files carefully honed over several years, because I forgot to save them from the old computer. And the eBay seller from whom I ordered a PCI Express sound card yesterday so that I could get going on digimodes again sent an old-fashioned PCI version just like the one I already have. His response to my complaint is "We have sold many of these and you are the first customer to have a complaint" which makes me feel like the mistake was my fault. I really am thoroughly fed up and wish now that I had just struggled along with the old, slow computer.
However it has not all been bad news. At the weekend whilst investigating all the available options I stumbled across this USB Sound Adapter from Digital Daffodil. At a price of £2.49 it seemed worth a gamble, though the post and packing at £3.45 more than doubled the final cost.
This also arrived today. I plugged it in and it "just worked" - Windows didn't even ask to install any drivers. I then hooked it up to the K3 and immediately began decoding digital signals.
The input is only for a microphone, not a line input, so it is very sensitive. This means I have to run the K3 line output at a very low level - 2 or even 1 - which should avoid the problem of distortion harmonics that I have observed at higher settings.
My IMD Meter shows that the transmitted PSK31 IMD is as low as it was when using the old computer and a "real" sound card. In fact, I inadvertently tested at 100W PEP output and the IMD was -28dB which is still pretty acceptable (I normally get -34dB at 25W PEP out on 20 metres.) So despite my initial belief that something this cheap couldn't possibly be any use I'm forced to conclude that it is actually perfectly acceptable.
I don't know what the maximum sample rate of this device is. I doubt that it is high enough to use for SDR decoding such as my project to use a SoftRock as a K3 panadapter, so I suppose I do still need a PCI Express sound card. But I'm not in a position to use it at the moment so the idea of returning the card I was sent and asking for a refund is quite tempting.