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The Duet Deluxe from above and slightly to one side: a square tea tin with a mottled dark blue border and a cream panel painted with a bird, a purple peony and green leaves. Set into the lid are two black knobs, two toggle switches, two small dark photocell windows, a round LED, two chrome jack collars, and a black lead that stands up out of a grommet and ends in a metal ring terminal - the touch probe. One painted side of the tin, showing long-tailed birds, is visible below.

Light-controlled noise box · One of a kind

Duet Deluxe

Synth Available · 1 of 1

Two 555 theremins in a tea tin, wired together by nothing but light. One sets the tempo, the other makes the tone, and a home-made vactrol - an LED and a photocell sealed face to face in the dark - lets the slow one bend the pitch of the fast one. Two more cells look out through the lid, so your hands play it without touching it.

  • TypeTwo-voice light-controlled noise box
  • ControlsTwo knobs and two toggles on the lid, two photocell eyes you play with your hands, and a bare touch probe on a flying lead
  • Circuit2× NE555 astable, coupled by a home-made vactrol
  • ExtrasLM386 amplifier and a mini mixer with a line in, and a speaker behind a grille drilled into the base
  • OutputQuarter-inch line out, switching – plug in and the internal speaker cuts out
  • EnclosureDecorative tea tin - the lid is the panel
  • BoardSolderable breadboard
  • Power9V battery, inside
  • BuiltSeptember 2026
  • StatusOne of a kind. When it is gone it is gone
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What it does

Both halves are NE555 timers running as oscillators. The slow one ticks, and how fast it ticks depends on how much light falls on the first eye. Its output drives an LED sealed against a photocell in a light-tight wrap, and that cell is the timing resistor for the fast one - so every tick bends the pitch of the voice. A third cell sits on the same node with its face out through the lid, so a hand over it plays the note directly.

It is not subtle and it does not stay still. Cover an eye and it swoops, shade it and it chirps, put a hand over both and it drops to a slow tick. Because it is reading the room it never plays the same way twice - move it to a different lamp and it is a different instrument.

There is an amplifier and a small mixer inside with a line in, so something else can play through it alongside, and it speaks out of its own speaker behind a grille drilled into the base. There is a quarter-inch line out as well, and it is a switching jack: put a cable in and the internal speaker cuts out, so it goes straight into an amp, a pedal chain or an interface without needing a microphone in front of it.

There is a touch bend as well. The mixer inside had a third channel going spare, so there is a bare probe on a flying lead, soldered to the end of that channel's mixing resistor and brought out through the lid. Hold the probe and the bare metal of the tin at the same time and it squeals - your own skin is part of the path, so it is never quite the same twice. Touch the probe against one of the toggle switches instead and it growls. Two more sounds out of one wire, both played by hand.

Demo

Demo filmed by Onion Madder on the actual unit.

How it was built

This one is documented end to end. The circuit started on a solderless breadboard, where the modifications got worked out, and then moved onto a solderable board and into the tin. The whole build is written up as a free guide: the Opto Duet on a breadboard - parts list, every step, the vactrol, and what each modification does.

So you can buy this one, or build your own from the same page. Both are fine by me.