Jc-120 Schematic Apr 2026

She found it tucked behind the peeling fiberboard of her late father’s workbench, sandwiched between a dead 9-volt battery and a dog-eared copy of Guitar Player magazine. Her father, Silas, hadn’t spoken to her in eleven years. He hadn’t spoken to anyone, really. He just repaired amplifiers for ghosts—old men with tremors and vintage Les Pauls who wanted to hear their youth one more time before their hearing went.

She traced the lines with her finger, following the power supply. +15V, -15V. A split rail. Symmetrical. Like a pair of lungs inhaling and exhaling at once. That’s where the story twisted.

She realized what he had built.

And some goodbyes are not endings. They are just the second voice, arriving late, trying to catch up. jc-120 schematic

The paper was the color of weak coffee, stained along the edges where someone’s thumb had rested for decades. It smelled of solder smoke, basement ozone, and the faint ghost of a 1985 Marlboro. To anyone else, it was a schematic: the Roland JC-120 Jazz Chorus. A grid of lines, triangles, circles, and Japanese characters that looked less like engineering and more like a map of the stars.

The night she powered it on, she didn’t plug in a guitar. She plugged in a microphone. And she spoke into it.

The JC-120 hummed. Then the chorus engaged. Two signals, slightly out of phase. One voice—hers—arriving a fraction of a second after the other. But her father’s modification, the red-ink change to the clock generator, had stretched that delay. Not to a slapback echo. To something else. The second voice arrived 2.7 seconds later. Then a third. Then a fourth. She found it tucked behind the peeling fiberboard

She didn’t understand until she built it.

She started at the input jack—top left. A simple ¼" TS. Then a JFET transistor, 2SK117. She remembered her father’s journals now: “The first gain stage must be silent. No hiss. No prayer. Just the string.” The signal then split. That was the secret of the JC-120. Not one path, but two. The famous stereo chorus was born from a bucket-brigade device (BBD), the MN3002. A chip that literally passed voltage like a line of firefighters passing a bucket of water from input to output. The clock speed of that transfer created the shimmer—the microscopic delay that made the sound wider than a cathedral.

R117: 1k (no, 2.2k? no—silence) C23: 47uF (replace with 100uF, bleed faster) D4: 1N4148 (remove. bridge. let it flow both ways.) He just repaired amplifiers for ghosts—old men with

A cough. A chair creaking. The sound of a Zippo lighter.

A memory amplifier.

Her father’s voice, buried in the tail of her own sentence, saying: “There. Now you can hear me when I’m not here.”

She sat on the garage floor, listening to her own words decay into noise. And then, between the 127th and 128th repeat, she heard something else.

The JC-120 had been his obsession. A solid-state behemoth from 1975. Stereo chorus that sounded like angels falling down a staircase. Clean headroom for days. No tubes to replace, no temperamental heat. Just pure, crystalline, unforgiving clarity. Silas used to say, “A tube amp lies to you. It warms up your mistakes. But the Jazz Chorus? The Jazz Chorus tells the truth.”