Boss CS-3 Compressor Sustainer
OTA compressor with tone control — the workhorse on pedalboards for 35+ years.
We don't ship reference schematics until they've been hand-authored against authoritative sources (manufacturer service docs, ElectroSmash analyses, GEOFEX writeups) and reviewed in the simulator. Until then, the BOM, signal chain, controls and mod notes below are accurate, and you can still add this pedal to a project — it just won't include a circuit yet.
About
A Boss-style FET-bypassed compressor built around an NJM2073 / M5207 OTA (operational transconductance amplifier) acting as the variable-gain element, with a full-wave-rectified envelope follower controlling it. A simple high-shelf Tone control restores brightness that compression naturally rolls off.
Signal chain preview
5 stagesQuick facts
- Replaces the earlier CS-2 (1981); both are still in production-style demand on the used market.
- Common 'Keeley mod' replaces the NJM2073 with a higher-quality op-amp and improves the tone-control voicing.
- Works equally well on guitar, bass, and synth — common on Nashville session boards.
Controls
- Level
- Tone
- Attack
- Sustain
Mod recipes Pro
3 mods- Keeley mod
Lower noise, smoother attack, better tone-control range.
How: Replace NJM2073 with a TLC2272 (drop-in). Change the tone-cap from 0.0033 µF to 0.0047 µF for a usable midband sweep. Bypass the input coupling cap with a 0.1 µF film for low end.
- Blend control
Parallel-compression for transparent dynamics.
How: Wire a 50k linear pot mixing the compressed wet signal with a tapped-off dry signal at the output buffer input.
- Faster attack switch
Pluck definition for funk / chicken-pickin'.
How: Add an SPDT switch in series with a 2.2 nF cap parallel to the envelope follower's smoothing cap to shorten the attack time.