Jc-120 Schematic ^new^

The Roland JC-120 Jazz Chorus schematic represents more than just a wiring diagram; it is the blueprint for the "King of Clean," a solid-state powerhouse that has remained in production since 1975. Understanding its circuit is essential for both maintenance and appreciating how it pioneered the modern chorus effect. Overview of the JC-120 Architecture

• Dead chorus (often the BBD chip: MN3004 or MN3204)
• Noise issues (transistors: 2SC458 → notorious for becoming noisy)
• Power amp failures (STK power packs)
• Hum (filter capacitors)

1. Power Amp Section: The power amp section is based on a push-pull configuration, utilizing four EL34 power tubes (or alternatively, KT77 or 6L6) in a Class AB1 configuration. The power amp is driven by a combination of two 12AX7 and one 12AT7 preamp tubes.
2. Preamp Section: The preamp section features three 12AX7 tubes, providing two channels (Clean and Overdrive) with independent gain controls. The Clean channel offers a transparent, articulate sound, while the Overdrive channel delivers a rich, distorted tone.
3. Master Volume and Tone Controls: The master volume control allows for overall level adjustment, while the tone controls (bass, middle, treble) provide precise EQ shaping.

Guide to Obtaining & Understanding the Roland JC-120 Schematic

1. Why the Schematic is Popular

The JC-120 (1975–present) is famous for its sterile clean tone and built-in stereo chorus/vibrato. Techs need the schematic to troubleshoot: jc-120 schematic

Scenario B: Only one speaker works