Jc-120 - Schematic

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This article is a deep dive into the Roland JC-120 schematic. We will explore the history of its revisions, break down the signal path block by block, discuss common failures, and explain how to read the schematic to breathe new life into your classic amp. jc-120 schematic

: This is the heart of the amp. It uses Bucket Brigade Device (BBD) chips—traditionally the MN3007 or MN3002—to create a short, modulated delay. The schematic reveals a unique "dry/wet" split where one speaker carries the dry signal and the other carries the modulated signal, creating an acoustic chorus effect in the air.

Integrated circuits (ICs) replace many discrete parts for easier manufacturing. Configuration: 2 x 12" Silver-cap speakers. Weight: Approximately 61.73 lbs (28 kg). Inputs: High and Low sensitivity for each channel. JC-120 | Jazz Chorus Guitar Amplifier - Roland Ensure your PDF contains: AI Mode history New

The JC-120 uses a dual-mono power amp design. Each channel is essentially a discrete solid-state amplifier using a complimentary pair of power transistors (such as 2SD-425).

The input stage uses Field Effect Transistors (FETs) and operational amplifiers (op-amps) to handle the guitar signal. : This is the heart of the amp

An LFO circuit generates a continuous sine or triangle wave, modulating the clock frequency to create pitch fluctuations (vibrato).

A streamlined clean path featuring High and Low inputs, a Bright toggle switch, Volume, and a 3-band (Treble, Middle, Bass) passive tone stack.

Over the years, the JC-120 schematic has undergone changes, often categorized by the service manual "editions":

[Guitar Input] ──> [Preamp Channel 1 (Clean)] ───────────────┐ ──> [Preamp Channel 2 (FX)] ────> [Chorus] ──┼─> [Dual Power Amps] ──> [Dual Speakers] 1. Dual Preamp Channels (CH-1 and CH-2)