Jc-120 Schematic Here

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.

She realized what he had built.

It took her three months. She learned to solder from YouTube videos. She burned her forearm on a soldering iron, cried over a misplaced capacitor, and learned the difference between tantalum and electrolytic the hard way—the former explodes if you look at it wrong. She sourced original MN3002 chips from a seller in Osaka who asked no questions. She etched her own PCB in ferric chloride, watching copper dissolve like guilt. jc-120 schematic

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.”

The BBD chips, starved of their proper clock voltage and given a new, erratic pulse, didn’t just delay the signal. They stacked it. Every word she spoke was repeated, but each repetition was degraded, filtered, darkened. After twelve repeats, her voice sounded like an old recording. After thirty, like a whisper from a tunnel. After a hundred, like static with a shape. The paper was the color of weak coffee,

R117: 1k (no, 2.2k? no—silence) C23: 47uF (replace with 100uF, bleed faster) D4: 1N4148 (remove. bridge. let it flow both ways.)

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. A grid of lines, triangles, circles, and Japanese

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