_top_ - Jc-120 Schematic

Roland JC-120 Jazz Chorus Go to product viewer dialog for this item.

The most complex part of the JC-120 schematic is the Chorus section. It relies on a clock generator (MN3101) and a BBD (MN3004 or MN3007). The schematic shows how the LFO (Low Frequency Oscillator) modulates the clock frequency, shifting the signal's time delay. jc-120 schematic

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• Input impedance: 1MΩ (R1, R2)
• Tone stack: Bass (100k log), Middle (50k log), Treble (100k log) – passive FMV style but with different cap values (C9, C10, C11 ~ 0.047µF, 0.022µF, 470pF)
• Chorus BBD: Usually MN3004 (512-stage) for delay A, MN3007 (1024-stage) for delay B – creates two-phase modulation
• Output transistors: 2SD718 (NPN) / 2SB688 (PNP) – TO-3P case. Replace with MJL3281A/MJL1302A if unavailable.

Print it out. Use a highlighter. Trace the signal path. The JC-120 is 40 pounds of wood, glue, and silicon, but with its schematic, it is repairable. Without it, it is just a very heavy doorstop. Roland JC-120 Jazz Chorus Go to product viewer