An upright pink sparkle box photographed face on. Three silver knobs run down the left side of the face; down the right, a small black LED bezel at the top, then three chrome toggle switches, with devils triangle lettered vertically in pale pastel letters beside them. At the bottom, a small 3.5 mm jack on the left and a black DC socket on the right.

Triple op-amp drone · One of a kind

Devil's Triangle

Synth Available · 1 of 1

Paul Stevenson's Devil's Triangle: three op-amp oscillators fighting over one output, on my own stripboard layout. Paul says the channel-level pots are useless, so they are gone, and in their place is a bend of mine: two toggles that lean the oscillators into each other through a kilohm. Two switches, four states, and the box is a different animal in each one.

TypeThree-oscillator drone, all op-amp, on stripboard
BoardMy own layout of Paul Stevenson's circuit, the free Devil's Triangle guide
ControlsThree pitch knobs down the left; down the right, two bend toggles and a power toggle, and an LED
Output3.5 mm jack on the face, bottom left. Line level, into an amp, an interface or the next box along
Enclosure125B, stood upright, pink sparkle, the name in pastel lettering down the side
Power9V DC, barrel jack on the face, bottom right
BuiltSeptember 2026
StatusOne of a kind. When it is gone it is gone

$60 free shipping Email to Buy

What it is

Three identical oscillators built around op-amps, each with a pitch knob, all summed to one output. On their own they are three tones. Set two of them near each other and they beat; set all three near and it turns into something that moves on its own.

The bend is the reason to have this one rather than build it. Pitch pot 3's first lug is the hub: a 1K and a toggle to pot 1, and another 1K and a toggle to pot 2. Straight through, the op-amp outputs would fight and one would win; through a kilohm they lean on each other and blend. With both toggles on, all three try to lock, and because the timing caps are identical they nearly manage it, which is where the good noises are.

The controls

Pitch 1, Pitch 3, Pitch 2, top to bottom down the left, each one oscillator. Bend 3-1 and Bend 3-2 are the two upper toggles on the right; the third toggle is power. The LED at the top is on when it is on.

The box

A 125B stood on end, pink sparkle, everything on the face so it can stand shoulder to shoulder with the other upright boxes. Output on the bottom left, power on the bottom right. No speaker inside; it goes out a 3.5 mm jack to whatever you plug it into.

Demo

Demo video coming soon - it's on the bench being filmed.

Or build it yourself

The layout, the parts list and the bend are all in the free Devil's Triangle guide, with the file you can open in Copper Bottom before you cut a strip. Paul Stevenson's original is credited there.