Here's a must have effect for any SA-1 - I just tried it today and it sounds awsome.
First of all you must have done the following mods (all have been discussed prior on this thread):
a) the sa-1 must have the voltage mod crash, or some other bend that causes the machine to crash.
b) the 'dj synchro distortion mod' should be installed.
If you have a SA-1 with both these mods then I urge you to build a LFO with a 555 and DIY Vactrol and then run the (+) side of SA-1's audio through the light dependant resistor side of the vactrol before connecting it to the speaker or jack. The 555 timer circuit will need to attached to part of the keyboard somewhere to gain its power, preferebly configured so you can turn it on and off with the keyboard's power switch.
When this is set correctly the DIY LFO will act as a 'gapper' effect on the audio and you can change the rate by the pot. Just playing the piano or synth waves sounds good. However what really sounds amazing is if you crash the keyboard so you have white noise or some thing similar - you can then sweep the noise with the distortion mod whilst simultaniously lowering the rate of the gapper, then when it's most distorted (and missing the high frequencies) you can decrease the distortion whilst increasing the rate of the gapper. It sounds very cool - try it!