While the JC-120 is famous for its reliability, the schematic can be complex for technicians, especially in managing the stereo interaction between channels, making it a project that requires familiarity with Roland solid-state design.
The JC-120 schematic’s most famous section is the analog chorus, which uses a "Bucket Brigade Device" (BBD) chip.
Always match and board marking (e.g., “JC-120B”).
While many play the JC-120 for its stock sound, it is a popular platform for modifications.
[ Input 1: Normal Channel ] ---> [ Mixer ] | [ Guitar ] v [ Left Power Amp ] ----> [ Left Speaker ] ^ [ Input 2: Effect Channel ] -------->| v [ Right Power Amp ] ---> [ Right Speaker ] ^ | [ Analog Chorus LFO ] The schematic is divided into four primary building blocks: A high-headroom, low-distortion preamp. jc-120 schematic
Uses 4558 or equivalent low-noise dual op-amps.
Given that Roland still supports (to a limited degree) these legacy amps, you have a few options for obtaining a clean JC-120 schematic:
The JC-120 schematic, also known as the "JC-120" or "JCM120" circuit, is a type of amplifier circuit designed by Marshall Amplification, a renowned British company known for its high-quality guitar amplifiers. The JC-120 circuit was first introduced in the 1980s and quickly gained popularity among guitarists and music producers due to its versatility, reliability, and exceptional tone.
The JC-120 schematic is a highly influential and widely used amplifier circuit that has been a staple in the music industry for decades. Its versatility, reliability, and exceptional tone have made it a favorite among guitarists, music producers, and electronics enthusiasts. By understanding the design and components of the JC-120 schematic, music equipment builders and DIY electronics enthusiasts can unlock the secrets of this legendary circuit and create their own high-quality music equipment. While the JC-120 is famous for its reliability,
The JC-120 schematic has been widely used in various music equipment, including:
A fundamental part of the JC-120 tone, this switch on the schematic adds a high-frequency boost, crucial for the "chimey" sound. 2. Preamp Circuitry (AP-44 Board) The preamp is generally divided into two channels:
The LFO creates a smooth sine or triangle wave. In "Chorus" mode, the LFO speed and depth are fixed to Roland’s factory-optimized sweet spot. Switch the amp to "Vibrato," and the schematic routes control back to the front-panel Speed and Depth potentiometers, allowing the user to adjust the frequency of the LFO modulation. 4. Power Amplifier and Output Section
Here are some sample JC-120 PCB layouts: While many play the JC-120 for its stock
If you are looking at a JC-120 schematic to repair an amp, these are the most common failure points:
Because the JC-120 uses specific components (such as obsolete BBD chips), having the correct schematic is crucial for diagnosing issues in the chorus, power supply, or distortion sections.
Always verify that a found schematic matches your specific amp revision based on the identification guide above before you begin any work.
Each power section utilizes a push-pull driver stage operating with rugged, discrete bipolar output transistors (often 2SB/2SD series pairs).
