The LittleBits Synth Filter is basically a Korg MS20 filter. I was about to build my own MS20 Eurorack filter based on one of the many designs online, but then I remembered I already had a Korg MS20 filter in my LittleBits kit. I soldered directly to the +5v input, ground, signal in, signal out, and CV control in, connected the in/out/control to three 3.5mm jacks, wired up a Eurorack power connector to get the +5v and ground, put an LED inline with the power with a 330ohm resistor, soldered it all to a breadboard, wire tied the filter to the breadboard, and called it a Eurorack 1U filter panel. It works great. If you buy the filter from the LittleBits website it's only $17. I would have definitely spent more than $17 just on the opamps, LM13700, caps, and transistors.