Danger

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With steckfeld you can connect your synth to the breadboard. There are two input mixers and two output mixers. The reference voltage for the output mixer can be adjusted for level shift the signal.

Danger

This is a work in progress module and might not work as expected. Feel free to file a bug report on the github page.

construction

I don't like working with breadboards. But sometimes you want to test things before you order a PCB. Connecting existing modules to the breadboard is especially tedious and building blocks like input mixer or output buffer occur in most circuits. This is where Steckfeld helps. It provides connectors for the patch cables and the necessary circuits for input and output. First, I made the resistors pluggable. But I never replaced them and finaly soldered them in.

the circuit of the attenuverter is based on the opamp dfferential amplifer. the two resistors at the non-inverting inputs are replaced with a potentiometer. the potentiometer is configured as a voltage divider and replace R3 and R4 from the differential amplifier. when the position of the potentiometer is adjusted, the output voltage will change or invert. at the center position the output is zero volrs. the response to the potentiometer is linear. we can make it an centered s-curve by adding two parallel resistors (R5,R6) to the potentiometer [[2][2]].

a simulation with the resistance at RV 1 changed from 0-100%. first run is the linear result. the second run is done with the resistors R5 and R6 added. This results in a s curve. the shape of the curve can be changed with the values of the resistors.

Figure 3: Steckfeld Board

BOM

main

#	reference	value	description
2	C1 C2	22u	Aluminium Electrolytic Capacitor, 35V, D=5 mm, LS=2 mm
6	C3 C8 C9 C10 C11 C12	47u (NP)	Connector_PinSocket_2.54mm:PinSocket_1x02_P2.54mm_Vertical
4	C4 C5 C6 C7	0.1u	Multilayer Ceramic Capacitors MLCC
1	J1	IDC Header	Pin Header IDC, 10 Pos, 2.54mm
6	J2 J3 J4 J5 J9 J10	IN	elektrophon:Jack_3.5mm_WQP-PJ398SM_Vertical
1	J6	Conn_01x02_Female	Connector_PinSocket_2.54mm:PinSocket_1x02_P2.54mm_Vertical
3	J7 J8 J11	Conn_01x04_Female	Connector_PinSocket_2.54mm:PinSocket_1x04_P2.54mm_Vertical
2	R1 R2	10	Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P2.54mm_Vertical
12	R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14	100k	Connector_PinSocket_2.54mm:PinSocket_1x02_P2.54mm_Vertical
4	RV1 RV2 RV3 RV4	R_POT	Potentiometer_THT:Potentiometer_Bourns_PTV09A-1_Single_Vertical
2	RV5 RV6	100k	Potentiometer_THT:Potentiometer_Bourns_3296W_Vertical
2	U1 U2	TL072	Package_DIP:DIP-8_W7.62mm_Socket