The Moog 984 Four Channel Mixer is sometimes called a Matrix Mixer because any of the four inputs can be mixed to any of the four outputs.  Maximum gain through any of the channels is 1.25 with the bass and treble controls centered.  There are a couple of errors on the schematic so I corrected them in this PDF file.

Corrected 984 Four Channel Mixer schematics

There is a Moog 984 4 Channel Mixer on Muffwiggler about a very nice redesign of the 984 mixer by David Ingebretsen.

Each PCB supports two channels.  There is an identical PCB without the edge connector on the left side of the module.

Operation

I swept my MOTM-300 from 5 to 4.4KHz and used the FM sweep to to drive the mixer to visualize the effect of the bass and treble controls on the frequency response.  This scope image shows the flatness of my input signal.

I set the Input level on the Moog 984 to 5 so I would have some headroom for the boost and the output to 10.  I adjusted the scope to show about the same XY display size.  This scope image shows the flatness of the frequency response with Bass and Treble set to 5 (middle).

This scope image shows the frequency response with Bass at 10 (maximum) and Treble at 0 (minimum).

This scope image shows the frequency response with Bass at 0 (minimum) and Treble at 10 (maximum).

I created some composite scope images with the controls at various settings.  In this scope image the Treble control is at 5 (middle) and the red is the Bass control at 0 (minimum), yellow is the Bass control at 5 (middle) and green is the Bass control at 10 (maximum).

In this scope image the Bass control is at 5 (middle) and the red is the Treble control at 0 (minimum), yellow is the Treble control at 5 (middle) and green is the Treble control at 10 (maximum).

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