After much digging around on 'tinterweb', I found that the solution was to remove the following entry for alsa in the following file:
Removed the entry:
Saved the file, rebooted the Pi (I don't think the reboot is essential though) and all now works perfectly! Hope this helps you.
I recently encountered a very similar issue on my rather ancient original Raspberry Pi (512Mb mem/single core) and the above recommendations failed to work. In the end, I had to edit the /boot/config.txt file and add the following entry: