When you are dealing with varying input and output loads, an active circuit is really the only way to go.  Here's a block diagram of the circuit. There's really nothing very fancy going on here. The actual mixing takes place at the two resistors that feed the output buffer and the mute switching occurs at X and Y.  The fet buffer circuits are very similar to this (very famous) Don Tillman circuit. I think the cool part is really the mute and led switching... Oh and by the way, the SPDT "AND" stompswitch that I used is the original (not-true) bypass switch form my old Dod 201 phaser.

Active ABY Box

Active ABY Box

Many of the tunes that I programme for the band have a bass part that is available on a seperate channel from the rest of the sequence.  This is so that I can run that track back into my bass amp on stage.  I used to use a simple (passive) AB box to switch between the synth bass from my laptop and my live bass, but I found that I wanted the option of playing over the top of those sequenced bass parts.  Especially after I bought my Akai Unibass! This pedal is esentially a two channel mixer.  I use the green channel for the sequenced bass and the red channel for my live bass.  I put a volume control on the green channel as I think its easier to tweak a knob than to turn around to the computer and put the mouse on a virtual slider.

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When you are dealing with varying input and output loads, an active circuit is really the only way to go.  Here's a block diagram of the circuit. There's really nothing very fancy going on here. The actual mixing takes place at the two resistors that feed the output buffer and the mute switching occurs at X and Y.  The fet buffer circuits are very similar to this (very famous) Don Tillman circuit. I think the cool part is really the mute and led switching... Oh and by the way, the SPDT "AND" stompswitch that I used is the original (not-true) bypass switch form my old Dod 201 phaser.

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