The Blender is based on an original design called The Phantom Pain audio router. Which, in turn, used the audio pathway of Earthquaker Devicesʼs Disaster Transport Sr. Delay pedal with a “modular” circuit that makes it possible to incorporate any three effects of your choice.
Let’s see how this creative invention works:
Send/return A is always in parallel with send/return B. Send/return C is still in series with effect B.
The Blend knob lets effect A stay parallel with effects B and C, mixes the parallel A and B into effect C, or allows a combination of series and parallels.
The original author suggests that it might be worth trying to have switching jacks for send/return B and wire them up so that when there is nothing plugged into the jacks, the send goes directly to the return pad. Though he hasn’t tested himself, it could be a good option if you feel like trying because this modification would create a standard series/parallel pedal with two effects.
If you plan to make this a standalone, modular pedal, you might need to use a 1590BB due to all the jacks you need (2 for each send/return and 2 for the in and out).
For further analysis on this circuit, take a look at this thread on Free Stomp Boxes Forum.