This is the Behringer SYSTEM 100 121 DUAL VCF Module. An authentic reproduction of the original “System 100M” circuitry from the 80s that can fit in a standard Eurorack case. The best part? It’s at a very affordable price. Mix the 121 DUAL VCF in with your existing rig or start your modular synth journey from here. Either way you’re sure to have a lot of fun.