Jc-120 Schematic 〈Safe 2024〉

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

Elena wasn’t a guitarist. She was an archivist. She organized dead people’s data for a living. So when she spread the schematic across her kitchen table, she treated it like any other document: source, signal path, output.

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.

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. jc-120 schematic

But schematics are not passive. They are stories told in the language of voltage.

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 chorus is a lie. The two voices are never equal. One always arrives late. That’s the beauty. That’s the tragedy. To fix it is to kill it. But what if I make the delay infinite?” R117: 1k (no, 2

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.

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

Elena turned off the amplifier. The silence was absolute. But the schematic was still on the table. And she understood now what he had been trying to say, not through words, but through voltage, resistors, and the cruel, beautiful architecture of a stereo chorus. let it flow both ways

She didn’t understand until she built it.

A memory amplifier.

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.

“Dad.”

Her father’s last journal entry, dated six years ago, wasn’t about a repair. It was a list. A Bill of Materials, but wrong.