In order to get this example of feedback I ran my suitcase model Rhodes, which I confine to my studio, through an outboard processor with some nice amp modeling and cranked up the gain. For the processing I used an eleven year old Yamaha A3000 sampler. The A3000 allows you to edit and apply processing to an incoming signal and it has some pretty nice sounding effects. Once I had adjusted the processing I held down the sustain pedal on the Rhodes and let the amplification do the rest. Tapping or gently knocking the instrument also produced some nice sounds. Here’s a snippet of the results.
Rhodes Feedback
This tiny sample of audio represents the instant that my iPod ran out of battery life while recording a performance of myself, Nils Westdal and Graham O’Brien on drums from Monday, November 17, 2008 at Cafe Barbette in Minneapolis. 
This afternoon I stumbled upon another one of my recent FM synthesis experiments from November 2, 2008. On that day I recorded eight minutes of output from select randomized programs that I produced using a MaxMSP patch called X.FM. You can hear all of the examples I have posted so far by clicking on the 
I top and tailed this clip of ambiance from a popular lunch spot in downtown Minneapolis, applying quick fades in the beginning and end of the twenty four second example. I also applied normalization to boost the levels. 
A couple of weeks ago, while working in the studio with Nils Westdal, we decided to experiment with an old amplifier that has a built in spring reverb. We plugged the direct out into a firewire interface and hit the record button in the software. Nothing was plugged into the amp, but by turning up the reverb knob all the way and the volume most of the way up, the spring reverb became very sensitive to vibrations. All that was left to do was to bang the amp around a bit while capturing the output.