VoltageProcessor

A eurorack module that outputs the sum and difference of two inputs, you can also add a constant DC offset to the summing output.

Motivation

The Beatstep Pro's pitch output cannot go lower than 2V, the VCO I'm using has a range of approximately 0-5V, so I had a way to subtract the 2V off of the pitch output. This module does just that, I intend to just use 1 CV input and a constant DC offset at -2V to achieve an output of 0V with a 2V input.
You could also use it as a small 2 -> 1 mixer.

Notes

This is my second KiCad project in a long time so the routing is not the best :)
Measured the current consumption at 1mA @ +12V and 7mA @ -12V

Bill of materials

Reference	Value	Qty
C1,C2,C3,C4	0.1uF	4
C5,C6	47uF	2
J1,J2,J4,J5	PJ301M-12	4
J3	Eurorack power	1
R1,R2,R3,R4,R5,R6,R7,R8,R9,R10,R11,R12	100k	12
R13,R14	1k	2
R15,R16	10k	2
RV1,RV2,RV3	100k	3
U1	TL074	1

Interactive BOM

Falstad simulation

Schematic

KiCad renders

rev 0.2 -> 0.3 patches

• DC Offset potmeter range is now +-10 instead of the rail-rail voltage.

rev 0.1 -> 0.2 patches

• Flip eurorack power connector around y-axis, I currently use a flipped power cable as a workaround.
• Switch U1B and U1B terminals by adding jumper wire and cutting trace.
• J4 and J5 output should be on pin 3 instead of pin 2. fix by adding jumper wire.

Todo

• All of the rev 0.1 patches
• Fix jack hole should be 6mm instead of 5.3mm.
• DC Offset potmeter compensate for opamp rail-rail offset which is around 1.3v
• Add polarity symbol in C5 and C6.
• Switch RV1 and RV2 twisting direction.
• Think about more ergonomic potmeter position.
• Front panel
• Produce and test rev 0.1

Resources

Summing Amplifier

Differential Amplifier