feedback loop ideas

[mako]

I am still pretty new in the world of lunetta's but I have made a matrix mixer to mix some oscilators and maybe other stuff...
The mixer is only 3 input and 2 output at the moment (i don't need more at the moment) and I'm looking for things to put in a feedback loop.
I already tried an opamp amplifier, but I have no idea what else I could use to get some nice sounds out of it...
Any suddestions?

p.s. this a video were i use the amplifier http://www.youtube.com/watch?v=5OXTUUo34Yc you have to put your volume high enough else you don't hear the music good enough

[Kabzoer]

Basically, everything that is active, some suggestions:
Linear CMOS: http://electro-music.com/forum/topic-47921.html
An active filter: http://electro-music.com/forum/topic-43897.html
Or a VCO: http://electro-music.com/forum/topic-43074.html
Just try a lot of different things