Modular Audio Mixer

ARC’s Modular Audio Mixer is a 4:1 AC mixer with discrete/op-amp plugins to change the circuit and audio character.  The module ships with five postage-stamp sized plugins; two of which are preassembled, and three for user experimentation.

Preassembled plugins:

• Discrete design based on the amplifier found in the Studer A80 mastering reel-to-reel machine from Switzerland.
• Metal can 741 op-amp design as found in early 1970s west coast synthesizers

Experimental plugins:

• Single channel op-amp board with DIP socket for μA741 style chips such as the OPA627, NE5534, TL071, etc
• Dual channel op-amp board with DIP socket for TL072 style chips such as the NE5532, OPA2134, etc
• Perf-board for user designs

Some additional notes:

• The discrete op-amp plugin uses Alfa metal can matched transistor pair, Elna Silmic II cap and hand picked resistors
• Module mA draw is given for the discrete op-amp, this can change based on other plugins
• The base design is an inverting mixer, so signals are phase inverted - the dual-channel experiment plugin only uses one channel of the op-amp, so is also phase inverted
• Plugin orientation is notated by a circle at pin 1 on the main PCB and the plugin cards.  All pins are labeled  as well
• No additional op-amps are included.  The experimental plugins offers access to the module's power rails, please don't goof with them if you aren't confident or do not have an op-amp's datasheet handy

Module Width	3hp
Mounting Depth	38mm
Current Draw	>5mA (+12V)
	>5mA (-12V)