If your transceiver has no VOX for PTT, or you prefer to keep the mic plugged in, and you have no problem working with tiny SMT pinouts, the USB Sound Adapter can also be modified to provide an audio-actuated PTT output as well as audio in and out:: http://www.usbradio.org/usbfob.pdf
This makes about as inexpensive a complete PSK31 interface as you can get! If you have any feedback problems, just add a Radio Shack isolation transformer in the transmit audio line. 73, Skip KH6TY >Hello Andy, >I have used almost the similar USB sound adapter and made a >modification to get a very high precision sampling rate. My module >has a 12 MHz crystal and CM108 codec inside. It was only necessary to >cut one of crystal wires and feed 3 V level from my double-ovened >reference oscillator (by resistance division from 5 V TTL). >73 Matti/OH2ZT
