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POLYKIT SYNTH DIY

Eurorack Output Module

Eurorack Modular Output Out Headphones Amplifier Through-Hole Kit
Table of Contents

The Eurorack output module gives you a versatile option to either connect your modular to a mixer or amplifier, or to drive some headphones with it. There are controls to attenuate the line-out and the headphone’s volume. The left input can be used as a single mono input.

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Key features
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  • 2-channel input (left channel mono)
  • 2-channel line-out
  • separate attenuation for line-out
  • headphones output with volume control
  • easy to build, all through-hole components
  • 4 HP

How it works
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The 2-channel line-out is the buffered input signal, and there are separate controls to attenuate them. Capacitors on the inputs block out any DC offset from the incoming audio signals. The headphones are driven by two 1A transistors on each channel, which allows low impedance, and there is a dual stereo pot for volume control.

Assembly
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The build is pretty straight-forward. The module only consists of through-hole components and is easy to assemble. There are three boards: a front panel, a board for controls/jacks, and a board for the circuit.

First, solder all parts on the component board. Keep the jacks and potentiometers for the end. Begin with the components with the lowest profile and work your way up. Screw the jacks and potentiometer to the front panel before soldering them. All components have a fixed designator and a component value printed on the board. Additional information on the parts can be found in the BOM below.

Make sure to use 1/2W 100 ohm resistors because there might be higher currents needed to drive the headphones. J3 on the control board needs to be a stereo jack for the headphones.

See the Component Basics guide for help identifying parts.

BOM
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Link to interactive BOM of the component board

ReferenceValueFootprintQtyDescription
C1100nCapacitor_THT:C_Disc_D5.0mm_W2.5mm_P2.50mm1Ceramic
C2,C310uCapacitor_THT:CP_Radial_D5.0mm_P2.50mm2Electrolytic
CONN1,CONN2~Connector_PinSocket_2.54mm:PinSocket_1x05_P2.54mm_Vertical25-pin socket, 2.54mm
D1,D2,D3,D41N4148Diode_THT:D_DO-35_SOD27_P7.62mm_Horizontal4100V 0.15A standard switching diode, DO-35
POWER1Conn_02x05_Odd_EvenConnector_IDC:IDC-Header_2x05_P2.54mm_Vertical1IDC 10-pin
Q1,Q3BC639Package_TO_SOT_THT:TO-92_Inline_Wide2NPN transistor, emitter/collector/base
Q2,Q4BC640Package_TO_SOT_THT:TO-92_Inline_Wide2PNP transistor, emitter/collector/base
R1,R2,R5,R622kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal41/4W 1% resistor
R3,R4,R7,R8100Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal41/2W 1% resistor
R9,R1010Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal21/4W 1% resistor
U1TL074Package_DIP:DIP-14_W7.62mm_Socket_LongPads1Op-amp, DIP-14

Link to interactive BOM of the control board

ReferenceValueFootprintQtyDescription
C1,C210uCapacitor_THT:CP_Radial_D5.0mm_P2.50mm2Electrolytic
CONN1,CONN2~Connector_PinHeader_2.54mm:PinHeader_1x05_P2.54mm_Vertical25-pin header, 2.54mm
J1IN_LConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles1Mono Thonkiconn 3.5mm jack sockets
J2IN_RConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles1Mono Thonkiconn 3.5mm jack sockets
J3OUT HPConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles1Stereo Thonkiconn 3.5mm jack sockets
J4OUT_LConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles1Mono Thonkiconn 3.5mm jack sockets
J5OUT_RConnector_Audio:Jack_3.5mm_QingPu_WQP-PJ398SM_Vertical_CircularHoles1Mono Thonkiconn 3.5mm jack sockets
R1,R21kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal21/4W 1% resistor
R3,R4100Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal21/2W 1% resistor
R5,R6100kResistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal21/4W 1% resistor
VOL_HP1100kPotentiometer_THT:Potentiometer_Alpha_RD902F-40-00D_Dual_Vertical1Dual potentiometer, separate units
VOL_LEFT1,VOL_RIGHT1100kPotentiometer_THT:Potentiometer_Alpha_RD901F-40-00D_Single_Vertical2linear, vertical, threaded, 6mm

Schematics
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