String machines: the cheapest way to get a huge analog pad

Before affordable polyphonic synthesizers existed, manufacturers solved polyphony with a trick: generate a single very high master frequency, divide it down with digital counters to produce every note on the keyboard at once, and let each key simply open a gate. That is a divide-down architecture, and it is the heart of every string machine built in the 1970s.

The result is not a polysynth. There is usually one filter and one envelope shared by every note — the definition of paraphonic. But for sustained string and choir textures, that limitation barely matters, and the design produces a sound that modern polysynths, oddly, still struggle to imitate.

Why they sound the way they do

Three things combine.

Every note is always running. Because the tone generators never stop, notes do not start from silence with independent phase. Chords lock together into a single, coherent mass rather than a stack of separate voices.

Divider circuits are perfectly in tune with themselves. Every octave is mathematically exact. That total absence of drift between octaves is why string machine chords sound glassy and slightly artificial in a way that is instantly recognisable.

The chorus is the instrument. Which brings us to the important part.

The ensemble chorus, and why it is not a chorus pedal

Ensemble circuits in string machines use bucket-brigade delay chips — analog shift registers that pass a sampled voltage from stage to stage, with the delay time set by a clock. Modulate that clock and the delay time wobbles, producing pitch variation. String machines typically run three BBD lines simultaneously, modulated by LFOs at different rates and phases, and pan them across the stereo field.

A single-line chorus pedal produces a periodic wobble that the ear recognises as an effect. Three lines at different rates never line up, so the ear hears width instead of modulation. That is the whole trick, and it is why bypassing the ensemble on a string machine leaves you with a thin, buzzy organ.

BBDs also add noise and roll off high frequencies with each stage. The compandor circuits used to fight that noise add their own gentle pumping. All of it contributes to the sound.

What they are good for, and what they are not

Good: sustained pads, string beds under a vocal, choir textures, slow chord movement, tape-adjacent lo-fi warmth.

Not good: anything requiring per-note articulation. Because the envelope is shared, playing a new note while a chord is held will not retrigger the attack for that note alone. Fast passages turn to mush. Bass duty is possible but the low end is usually soft.

Knowing this saves money. If you want one lush sustained layer, a string machine or a good emulation of one is the most direct route. If you want a workhorse polysynth, it is the wrong purchase.

Buying and maintaining an original

Vintage units are aging electronics with specific failure points. Check that every key sounds — dead notes often mean a failed divider chip, which can be hard to source. Listen for excessive hiss with the ensemble on, which points to tired compandor or BBD stages. Sticky or noisy sliders are usually cleanable; missing keyboard contacts are a bigger job.

Expect to budget for a service. Also expect the instrument to weigh more than you imagine, because most of these are full-size keyboards in wooden cases.

Getting most of the sound without buying one

If you already own a polysynth, you can get surprisingly close:

1. Use a simple sawtooth on every voice, no detune between oscillators.
2. Open the filter most of the way and use a gentle slope; string machines are not filter-driven.
3. Set a slow attack and a long release, and avoid velocity sensitivity entirely.
4. Add three separate short delays — roughly 8, 14 and 20 ms — each modulated by an LFO at a different slow rate, panned left, centre and right.

Step four is the one that matters. A single stereo chorus plug-in will not do it, because the whole point is that the three modulations never agree with each other.

Get that right and you have the pad. Everything else about the architecture is a historical detail.