level-gate-screamer

Tube Screamer-style overdrive with a level gate: attenuates below threshold, boosts above

Warning

v1: J2/J3 footprints are rotated 180°. Fix with jumpers on the bottom side:

• J2: 1–6, 2–5
• J3: 1–6, 4–2

Next revision: rotate J2/J3 so the big protrusion faces the board edge.

Output level: up to ~9 Vpp (rail-to-rail op-amps on 9 V). Check the input range of the next device before connecting. Tested OK with a Neural DSP Nano Cortex.

Files

• kicad_files/ — KiCad project
• fabrication/ — Gerber, BOM, CPL for JLCPCB
• hand_soldered_parts/ — parts not assembled by JLCPCB
• simulation/ — ngspice netlist

Images

Finished PCB

PCB just arrived

PCB layout (KiCad)

Schematic

Labeled as "OTA boost", but this isn't an OTA.

Level gate concept

Simulation: input above threshold (amplified)

Simulation: input below threshold (attenuated)

Impressions

• Sounds great
• Easy to play
• The gate works as intended

References

• UC3Music/IceScreamer — base Tube Screamer design and footprints
• ElectroSmash Archive: Tube Screamer Analysis
• ElectroSmash Archive: MXR MicroAmp Analysis — boost stage
• PCB Guitar Mania: No-Noise Gate building docs (PDF) — noise gate
• Elliott Sound Products: VCA Techniques Investigated — JFET VCA (Figure B)
• Boss NS-2 — gate idea: detect on the dry signal, mute after the gain stage