DRAFT - the wiring below is translated net for net from the verified 11×14 stripboard layout, but this breadboard version has not been built on the bench yet. Build it once, fix anything that fought back, then delete this banner.

Dual-Wave LFO

Triangle and square from one chip, on a breadboard · By Onion Madder · Mess O' Pedals

An LFO is the effect behind the effect: too slow to hear, it exists to wobble other circuits. This one makes a triangle and a square from the two halves of a single NE5532, chasing each other from 2.5 to about 8 Hz, with a rate knob and a blend knob that morphs between the two shapes. It is the first build in this series that makes no sound at all on its own - and the first with an op-amp.

This is the seventh build in the breadboard series. I planned it as an 11×14 stripboard layout first - a board that needed seven track cuts, every one of them just to keep the chip's two pin rows apart. On a breadboard the center channel does that job by itself, so all seven cuts simply disappear and the layout collapses to eight nets and eleven jumpers. Power is 9V - though 12 to 15V is genuinely better here, see the supply note before power-up.

What you'll need

The parts list lives on the build sheet too - this version adds how to spot each part: the printed marking, the package, or the polarity clue.

• 1× NE5532 dual op-amp, DIP-8 - spot it: 5532 in the part number on top, a notch at one end and a dot beside pin 1. An LM358 is the same pinout and is actually specified for a 9V supply - see the supply note
• 1× 47K resistor - sets the fast end of the rate sweep. Spot it: bands yellow-violet-orange
• 1× 68K resistor - trigger window, triangle side. Do not swap with the 100K. Spot it: bands blue-gray-orange
• 2× 10K resistors - the mid-rail divider; a matched pair matters more than the exact value. Spot them: bands brown-black-orange
• 1× 100K resistor - trigger window, feedback side. Spot it: bands brown-black-yellow
• 1× 1 µF film cap - the integrator cap; it sets the rate, so film, not ceramic. Spot it: a little box or oblong, either way round
• 1× 47 µF electrolytic, 16V or higher - bias decoupling. Spot it: a little can; the stripe marks the minus leg
• 1× 100nF ceramic - supply decoupling, not on the stripboard layout; added here because the NE5532 is a fast part and long breadboard rails are an invitation. Spot it: printed 104
• 1× 100K linear pot - rate. Spot it: marked B100K. Only the wiper and lug 3 are used
• 1× 1K linear pot - blend. Spot it: marked B1K or B102. All three lugs; its wiper is the LFO output and never touches the board
• A breadboard - all of it this time: both banks and both rail pairs. The build spans columns 2 to 22, so a half-size board fits. Plus about 11 jumpers, at least one of them insulated wire rather than a bare leg
• 1× output lead - tip and sleeve, to whatever you are wobbling
• 9–15V DC supply - a 9V battery works, but 12 to 15V is the better choice here and costs nothing in rate (see the supply note). Four salvaged vape cells in series land at 14.8V nominal, inside that window - untested on this build, so meter it first

Reading the breadboard

This guide names exact holes, like F10 or C22. Letters run across the board and numbers run along it, and both are printed on the board itself - the printed labels are the authority, whichever way up you hold the board. The five holes in a bank that share a number are one electrical point.

Unlike the rest of the series, this build uses both banks - the chip straddles the center channel, A to E on one side, F to J on the other - and both rail pairs. To keep the wiring unambiguous, the rails are named by their neighbors: the A-side rails are the pair beside row A, and the J-side rails are the pair beside row J. Red stripe is +, blue stripe is −, on both pairs. Before you wire anything, meter each rail end to end - plenty of boards break the rails at the midpoint, and if yours does, bridge the break with a jumper.

How it works, in one breath

Half the chip is an integrator: feed it a steady voltage and its output ramps at a steady rate - that ramp is the triangle. The other half is a trigger with a window set by the 68K and 100K: when the ramp crosses the window's edge, its output slams to the other rail - that slam is the square. And the square is what feeds the integrator, through the rate pot, so every slam reverses the ramp. The two halves chase each other forever, the 10K pair holds the halfway voltage the whole dance swings around, and the blend pot's wiper rides between the two outputs. Because the speed is set only by resistors and the film cap, raising the supply voltage changes the amplitude and nothing else.

The supply note, or the 9V problem

TI's NE5532 datasheet recommends a supply of ±5V to ±15V, and a 9V single supply is only ±4.5V - below the minimum, with about a volt of headroom left at the trigger's input. The stripboard original is verified and does run at 9V, but it is outside the part's spec. Since the rate formula has no supply term in it, running this at 12 to 15V costs you nothing and fixes it. If you are committed to 9V, use an LM358 - same pinout, and designed for exactly this.

What the rate pot gives you

The 47K plus the dialed-in part of the 100K pot set the ramp current. The film cap is the coarse control: 470nF roughly doubles every figure here, 2.2 µF roughly halves them.

What the meter should say

Every reading is judged against the bias at D17. On a 9V supply, bias is 4.5V; on 12V it is 6V - always half the rail.

Things to try

• Give it an eye. Hang a 4.7K resistor from column 22 (the square bus) to a spare column, and an LED from there to the blue rail - it pulses in time. The square is about 1.5× the triangle's size, so don't expect the blend to feel like a level-matched crossfade; that asymmetry is the design.
• Change the span. Swap the 1µF film for 470nF and every rate roughly doubles; 2.2µF and everything halves. The rate range is the one thing the supply voltage cannot touch.
• Wobble something. The output sits at half the rail - perfect as a control voltage into anything with a CV input. Into a pedal or an amp input, put a series cap after the wiper first, or the DC will thump.
• Feed the family. Point it at the Hive's inputs or an Optical Theremin's photocell (LED taped to LDR = homemade vactrol) and the LFO starts earning its keep.

The circuit came out of the Experimentalists Anonymous DIY archive, where synth schematics are kept alive. This breadboard recipe, the stripboard layout it was translated from, and the words are my own. Build it, bend it, make it yours.