Xenyx X1222USB : I started off wanting a USB audio interface for my PC

... and for not very much more I got an eight channel mixer with a USB interface. I also use it for small scale live work - 3 or 4 mics, keyboard and drum machine. My only complaint was that the FX send is taken post fader (fine) but pre-mute (not fine). This means that if you mute the microphone channels you still get the FX signal going into the main mix - which sounds a little disconcerting in live situation as you still have a background vocal echo in the PA and have to separately mute the FX to main mix.

However, this is no longer a problem as the FX unit now introduces a horrible low frequency square wave buzz virtually all the time. Only way to get rid of the buzz is to turn down the FX to Main and Monitor controls. Same thing has happened on a Behringer K450 keyboard amp as well, so I'm questioning the reliability of the generation of FX circuitry from around 2010 if two units have started oscillating in the same manner.