Jc-120 Schematic ((top)) May 2026

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

The Jazz Chorus Project: A dedicated community resource detailing the differences between the "B" (early), "M" (mid-era), and modern revisions. Common Repair Points jc-120 schematic

⚠️ Avoid scam “instant download” sites. Stick to known DIY repair forums (Freestompboxes.org, GroupDIY, MusicElectronicsForum). The Roland JC-120 Jazz Chorus schematic represents more

The Stereo Dimension

The JC-120 schematic is unique because it splits the signal into two paths after the effects section. Do not run it without speakers (STK modules

The MN3007 BBD Chip

The secret lies in the MN3007 IC (Integrated Circuit). This is a "Bucket Brigade Device" (BBD). On the schematic, you will see this large chip near the center of the effects board.

• Do not run it without speakers (STK modules can oscillate and self-destruct).
• Do not blindly change transistors – only swap noisy 2SC458s with KSC1845 (ECB pinout!).

• Tube Replacement: Replace power tubes every 500-1000 hours or as needed.
• Bias Adjustment: Adjust the bias circuit to maintain optimal power tube performance.
• Cleaning: Regularly clean the amplifier's exterior and interior to prevent dust buildup.

Most "stereo" amps use one power section to drive multiple speakers. The JC-120 has two independent power sections, each pushing 60 watts to its own 12-inch speaker. Phase Mixing:

The Mix

The schematic shows the "Dry" signal bypassing the BBD and the "Wet" (delayed/modulated) signal coming out of the MN3007. These two signals are mixed back together. Because the Wet signal is slightly detuned by the LFO, combining it with the Dry signal creates phase interference—this is the "swirling" Chorus effect.