There is a great thread taking place on VSE now concerning the meticulous restoration of a Hammond Novachord. What's a Novachord? Produced by Hammond in the 1939-1941 period, the Novachord is generally considered the first practical, mass-produced synthesizer.
Novachord undergoing restoration. All photos in this post are courtesy of D. A. Wilson.
A synthesizer in 1939? Yes, although herioc measures were required, and the instrument's reputation suffered for it. Surprisingly, the 144 vacuum tubes required for the note generation circuitry were generally not the problem. The Hammond engineers realized that the instrument would experience a tube failure every few hours if they designed the tube circuits per normal design practices of the day. They severely derated the tubes in order to increase the mean-time-between-failure from hundreds of hours to thousands (a technique that would appear again in the ground-breaking ENIAC computer a few years later), cutting the heater voltage from the nominal 6.3V to 5V, and limiting plate currents to a fraction of a milliamp. Here's what 144 tubes in one place looks like:
We'll get back to the reliability issue in a bit. First, let's go over the instrument a bit. Is it really a synth? Yes indeed, and a fully polyphonic one to boot; you can play all 72 notes simultaneously. Each voice has one oscillator that produces a sort-of saw wave, an ASR envelope generator, and what amounts to a VCA. (It isn't a VCA as we know it, in terms of actually feeding it a control voltage; the VCA and the envelope generator are both part of the same circuit. Nonetheless, it is an amplifier with time-variant gain, and it responds to the envelope generation and does what a VCA conventionally does in a modern synth.) Attack is controlled by panel controls, while release is controlled by pedals.
The filter section is paraphonic. There are three resonant bandpass filters, and several other filters for general tone control, that all of the voices feed into. The filters can't respond to the keyboard; they aren't voltage-controlled (that concept would have to wait another three decades for Moog and Buchla), so cutoff is controlled manually. The tradeoff is that they are true LC resonant filter circuits, and have a very definite effect on the sound. The overall effect is somewhat like a fixed filter bank on a modular synth.
A vibrato circuit serves more or less the same purpose as chorus circuits on modern synths. The vibrato is configured so that different notes are varied at different rates, which produces more of a chorusing effect when dense chords are played. The Novachord has a built-in amp and speakers (which unfortunately are underneath the case and aimed at the floor), and connections for external Hammond tone cabinets. (Which means that presumably a Leslie could be connected, although I haven't heard of anyone doing that.)
Here's a shot of the panel, with its stylish Bakelite pointer knobs. You can see from this panel that Hammond anticipated the ways in which synth control panels would be laid out decades later. In general, the controls are grouped with the filter controls on the left, and the envelope and vibrato controls on the right. In the photo below, two of the resonant-filter controls can be seen at the left edge, and the attack time knob is just to the right of the big downward-pointing knob:
Hammond made approximately 1000 of these beasts, which was actually a considerable number for the day, especially since production only ran for about three years. However, only a handful are known to exist today, and fewer still are in operable condition. Considering that in 1939 a Novachord cost considerably more than the average automobile, one might think that the people who bought them would have taken more care with them. One thing that might contribute to the few number remaining today is that the things are massive and heavy; no doubt some were abandoned (say, when the owner of a house containing one died) because they were so difficult to move. Another factor is that production was halted rather abruptly in 1942 after the U.S. entered World War II and some of the parts became restricted to military uses only; likely some Novachords were stripped for parts during and after the war.
However, another clue might be in this photo:
The resistors connected to that elegant key mechanism are carrying a whopping 270 volts. That was the plate voltage for the voice generating tubes. Which brings us to the actual waveform generation method used for the voices. The Novachord uses a top-octave division setup, but unlike top-octave architectures today, the octave division is not done using counter circuit -- that concept was unknown at the time. Instead, what it uses is a sort of hybrid between a top-octace divider and a VCO with a sync input. As mentioned previously, each voice has an oscillator which generates a decreasing (downward-sloping) sawtooth wave. The oscillators for the top octave are free running; their frequency is set by a resistor and a capacitor having very precise values.
Oscillators for the octaves below the top octave have a mechanism that will accept a hard sync input, but only after the oscillator has passed the approximate halfway point in its cycle. The signal from the next octave above is wired to the sync input. When an oscillator begins its cycle, it jumps to its maximum voltage and begins decreasing. When it reaches about halfway, the sync input (the waveform from the next higher octave) pulses, but the oscillator doesn't accept it yet. Its output voltage keeps decreasing until the sync input pulses again, at which point the oscillator will accept a sync input. At that point, it syncs itself to the octave above. Each oscillator syncs to the oscillator an octave above it.
It should be apparent that there are a lot of timing dependencies here, not only in determining the frequencies for the top octave oscillators, but in computing when each oscillator in the lower octaves has passed its halfway point and will accept a sync input. Unfortunately, the combination of the very high voltages and the paper capacitors that Hammond used (the only good alternative in those days was mica, which was prohibitively expensive) made the instrument's oscillator circuits very sensitive to temperature and humidity changes. Obviously, drift in a top octave oscillator would cause that note to go out of tune in every octave. But what was more distressing was "octave jumping", in which an oscillator would mis-sync, and not only jump that note to a different octave, but also the same note in all lower octaves, due to the way the synchronization was chained. Some sources also suggest that the fast-cycling relays in the vibrato circuits were prone to sticking and throwing the whole instrument out of tune.
It's actually rather interesting that the Novachord was created in the first place. Laurens Hammond was a music lover, but he was also a businessman, and he had originally gone into the organ business to create an additional market for the synchronous motors he had invented. But the Novachord contains no motors; in fact, other than the keys and the vibrato relays, it contains no moving parts at all. The circuitry is completely different from the Hammond organs, and there appears to be no parts commonality. Did Hammond really dream up a full-blown concept for a synthesizer in the 1930s, decades before almost anyone else? Maybe. It's a myth that Hammond was tone deaf; in fact, he had a keen ear for music and timbre, even though he himself did not play. He had learned quite a bit about tone and harmonics from the experiments leading up to the Model A, and perhaps the Novachord was what he saw as the next step down that path. Also, possibly, the Novachord was intended to be a technological pathfinder for future fully-electronic organs.
In any event, although apparently the company discussed an improved version of the Novachord to go into production after the end of the war, that never happened. And it would be quite some time before Hammond did anything in the direction of synths again. So Laurens Hammond left the electronic music world a rather strange legacy, an intriguing but peculiar footnote in synthesizer history. One can't help but wonder how that history might have been different had Hammond pressed the Novachord idea just a bit further.