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Project Specification — EQ Mix + Clean Boost Guitar Pedal
Project Overview
Status: Draft. Design a fab-ready 2-layer through-hole PCB for a DIY analog 9V guitar stompbox combining a fixed wet-path EQ, passive dry/wet blend, clean boost, and output buffer.
Intended Use
DIY hand-soldered guitar pedal PCB for 125B / 1590B style enclosures. 3PDT true bypass, LED, DC jack, audio jacks, and panel pots are wired offboard.
What the Device Should Do
- Accept guitar-level audio from a true-bypass footswitch wiring harness.
- Buffer the input, split into dry and wet paths, EQ only the wet path, then blend dry/wet via an external MIX pot.
- Apply clean boost after the mix, then buffer the output.
- Operate from a single 9V pedal supply with 4.5V virtual ground.
Main Features
- 2x TL074 DIP-14 quad op-amps in sockets.
- Wet EQ: 600 Hz 2nd-order HPF, +8 dB at 800 Hz, +8 dB at 1.2 kHz, 4 kHz 2nd-order LPF.
- Clean boost: roughly +1.2 dB to +17.9 dB via external 10k linear pot.
- Offboard 100k MIX pot, 10k BOOST pot, power, input, and output headers.
- Vref test point and labeled 2.54 mm headers.
System Architecture
Diagram
Hardware Subsystems
- Power/reference: 9V input header, 1N4007 polarity protection, 100k/100k Vref divider, 10uF and 100nF Vref bypassing, 100nF decoupling per TL074.
- Audio path: AC-coupled op-amp stages biased around Vref.
- External controls: 1x3 2.54 mm headers for power, input, output, MIX, and BOOST.
Interfaces and Connections
Table
| Header | Pins | Purpose |
|---|---|---|
| J1 PWR | 1=V9, 2=GND, 3=VREF | Offboard DC jack / star ground / Vref access |
| J2 IN | 1=signal, 2/3=GND | From 3PDT engaged input |
| J3 OUT | 1=signal, 2/3=GND | To 3PDT output |
| J4 MIX | 1=dry, 2=wiper, 3=wet | 100k linear pot |
| J5 BOOST | 1=Rf end, 2=wiper, 3=op-amp out | 10k linear boost pot |
Power and Runtime Expectations
Runs from a standard 9V guitar pedal supply. Current is expected to be dominated by two TL074 packages plus LED current wired offboard.
Power Tree and Power Budget
Diagram
Manufacturing and Assembly Expectations
- 2-layer FR4, 1.6 mm, target JLCPCB / OSH Park fabrication.
- Through-hole only, hand-solder friendly.
- U1 and U2 in DIP sockets.
- Board target: about 100 × 60 mm with four M3 mounting holes.
Firmware-Relevant Hardware Requirements
No firmware or digital logic.
Physical Design Expectations
- U1 and U2 centered side-by-side.
- Headers near board edges: power/input left; output/mix/boost right.
- Single ground pour with star-ground intent at J1 pin 2.
- Keep input trace short and route Vref away from high-gain boost area.
Important Design Decisions
- True bypass, LED, DC jack, jacks, and pots remain offboard.
- No charge pump or clipping stage.
- Hot pickups may clip at max boost on 9V rails; acceptable for this pedal.
Assumptions
- Library through-hole equivalents are acceptable where the exact TL074/connector MPN is not specified.
- Offboard wiring follows standard DIY true-bypass diagrams.
Change Notes
- Initial specification created from uploaded FLUX_PROMPT, CIRCUIT, STRIPBOARD, CALCULATIONS, and pasted requirements files.
Project Overview
Intended Use
What the Device Should Do
Main Features
System Architecture
Hardware Subsystems
Interfaces and Connections
Power and Runtime Expectations
Power Tree and Power Budget
Manufacturing and Assembly Expectations
Firmware-Relevant Hardware Requirements
Physical Design Expectations
Important Design Decisions
Assumptions
Change Notes
