Mix 04

Description

Mix 04 is an extensible 4 in / 4 out VCA matrix with a total of 16 transparent Blackmer VCAs. The matrix can route any input to any output. Several Mix 04 modules can be combined to make a bigger matrix.

Analogue Bus
Mix 04 features the new Rebel Technology analogue bus, allowing compatible modules to be interconnected without additional patching. Connect two or more Mix modules to create a mixer with more inputs and outputs. Balanced inputs and outputs can also be added, either for front panel mounting or built in to the modular case.

Description

The module features a 4×4 matrix of CV inputs, one for each input (vertically arranged) going to each output (horizontal). The level for the first input going into the first output is set by the CV input jack at the top left of the module. From top to bottom are the CVs for input 1 to 4, and from left to right for output 1 to 4.
The two rows of LEDs indicate the input and output levels respectively. The first row of jacks below the LEDs are the inputs, the row below are the outputs.

Bus
On the back of the module there are four 5-pin interconnect headers. Two 5-pin headers connect the input channels and normalled inputs. Normalling means that a connection can be made between two modules when nothing is inserted into the normalled jack. Inserting a plug into the jack breaks the normalled connection.
Two more 5-pin headers connect the outputs.
Connecting the input bus of two Mix 04 modules creates a 4 in / 8 out matrix. Connecting the output bus of two modules creates an 8 in / 4 out matrix. Both connections can be made at the same time, and bigger matrices can be created by connecting more Mix 04 modules.
Thanks to the normalling jacks, the modules can still be used independently while connected to the same input and output bus.

Outputs
The inputs and outputs are DC coupled, suitable for both audio and control voltage mixing and routing.

Calibration
The VCA response curve is exponential, with adjustable maximum and unity gain which can both be tuned over a wide range with two precision trim pots on the back of the module.
The module comes pre-calibrated with unity gain at 5V and +3dB gain limit.

Response Curve
The 16 VCAs are high-performance Blackmer amplifiers based on the 2164 chip, famous for its dynamic range and transparent audio quality. The response is exponential with adjustable slope and adjustable, soft limit (see Calibration).

The first plot shows the output from Mix 04 (blue trace) with a 5v DC input. The red trace is a 0-10V envelope going into the VCA CV input. The response is exponential, reaching unit gain at 5v, then tapering off to peak at 5V plus 3dB.

The second plot shows the same configuration with a 440Hz audio input.

Specifications

Dimensions

• Width: 10HP / 50.50mm
• Height: 3U / 128.50mm
• Depth: 35mm
• Weight: 120g

Power

• 10-pin Doepfer/Eurorack
• Reverse voltage protected
• +12v: < 110mA
• -12v: < 110mA

Impedance

• Outputs: <= 1k Ohm
• Inputs: >= 100k Ohm

Open Hardware

Mix 04 is Open Hardware, published under the Gnu GPL.

The schematics and BOM are publicly available on GitHub.
Please send your patches to us as pull requests and bug reports as issues on GitHub.