Jc-120 Schematic < Trusted × 2024 >

Feature discrete TO-3 "can" style power transistors (like the 2SD424). These are known for extreme reliability and high current delivery.

If you view the schematic for the power amp, you won't see a single chip amp like a TDA series found in cheaper practice amps. Instead, you see a "Discrete Solid State" push-pull design.

Mirrors Channel 1 but routes the signal into the onboard effects section (Distortion, Reverb, and the Chorus/Vibrato block). 2. The Distortion Circuit (The "Crackle" Effect)

The built-in distortion circuit on the JC-120 is historically polarizing. Looking at the schematic reveals why it sounds distinct from tube distortion. jc-120 schematic

: It utilizes two independent 60-watt power amplifiers, each driving one of the two 12-inch speakers. Preamp Design

The Roland JC-120 Jazz Chorus is a legend. Since its debut in 1975, its unmistakable "JC Clean" tone and lush stereo chorus have defined the sound of guitar for nearly five decades. Unlike many iconic amps that rely on warm tube saturation, the JC-120’s all-transistor design is celebrated for its pristine, powerful, and untouched reproduction of the guitar's natural voice. However, for the owners of these venerable amps, the key to their longevity lies in understanding their complex circuit, a task made challenging by the fact that the JC-120 was produced in a number of distinct revisions.

The Roland JC-120 Jazz Chorus Go to product viewer dialog for this item. Feature discrete TO-3 "can" style power transistors (like

The dry signal is sent to the Left Speaker. The pitch-modulated (wet) signal is sent to the Right Speaker. The chorus effect does not happen inside the wires; it mixes acoustically in the air between the two speakers. 5. Stereo Power Amplifier Section

Early JC-120s did not have speaker protection circuits, so catastrophic power stage failure could destroy the Roland 12-inch speakers. 5. Summary Table: JC-120 Specifications Specification Output Power 120W RMS (60W + 60W) Speakers 2 x 12" (30cm) Channels 2 (Channel 2 has Effects) Effects Chorus, Vibrato, Reverb, Distortion Inputs 2 x High, 2 x Low Stereo Loop Yes (Channel 2) Conclusion

Identical to Channel 1 but routes the signal through the Distortion, Reverb, and Chorus/Vibrato sub-circuits. 2. The Distortion Circuit (The "Trashy" Drive) Instead, you see a "Discrete Solid State" push-pull design

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.

If the amp turns on but blows fuses instantly, one of the dual power amplifier stages likely has shorted output transistors. Use the schematic to isolate the left and right power blocks to determine which side is failing.

The JC-120 has undergone several revisions over its 40+ year history. To ensure you have the correct diagram, check your serial number and physical features: The ultimate JC-120 thread

Always match and board marking (e.g., “JC-120B”).

The schematic of a JC-120 can be intimidating due to its component density. Breaking it down into functional blocks reveals its brilliant engineering. 1. Dual-Channel Input Stage