If you have on-board speakers onthe Farfisa and they work, and if the Peavy works with anything else plugged into it, then you either have a bad cord or there is something wrong with the "out" on the organ...the jack you use to connect to the amplifier via a cord. Try contact cleaner and look for an old connection that has failed or othe rnon-function of the connection jack.

Should be pretty easy to trce down, if you're getting sound out of the organ.

R.