A stroll into synth history

Mark Hammer · Joined: Mar 05, 2017 Posts: 11 Location: Ottawa, Canada

Through a series of acquaintances, I ended up with what some may consider a dream gig. I am working on the building of a replica of the world's very first voltage-controlled synthesizer, the "electronic sackbut", invented by physicist HUgh LeCaine, and built by him (at home, we think) between 1945 and 1948.

If you look up some of the many Youtubes on the device, you can see that the original appears very flimsy (I joke that it is held together with thoughts and prayers). It is currently on display (behind glass) at the National Museum of Science and Technology in Ottawa, Ontario. I got hooked up with a project funded to produce a working replica, that is as close to authentic as possible, using contemporary components. The original is tube based. And with the high-voltage circuitry and power supply, AND the chaotic wiring, AND the fragile state, it is an electrocution hazard waiting to happen. So a low-voltage replica with more organized circuitry would be nice. A digital sound engine replaces the tube-based oscillator/s. The goal is not necessarily to have it on display for visiting children to bash away on, but ultimately it WILL be available to musicians to book time with.

It's a mono keyboard, that uses a fairly standard (or rather, what was to BECOME standard, several decades later) resistor ladder. As much as there were electronic instruments prior to 1945, this one is identifiably the first voltage-controlled instrument ever made. It even has portamento. And while there is no pitch-bend and modulation wheels at the left end of the keyboard, it does have several finger-operated controls to work with your left hand, while your right hand works the keys.

The keyboard has very primitive forms of pressure and velocity sensitivity, and an interesting lateral pressure sensitivity, apparently for injecting modulation. Sadly, while LeCaine left boxes of notes, there are not schematics corresponding directly to the unit the museum has. LeCaine continued to develop and refine more advanced units, so the circuit drawings we do have contain a blend of the original circuit and ideas implemented in later synths that he devised, such that the circuit diagram we have is a composite and not directly translatable to the unit we are replicating.

So far, I have been working on the keyboard, which has proven to be a mechanical challenge.
Here's the original 49-key keyboard. The 100P resistors that form the ladder are connected underneath to the heads of the bolts sticking up. The hex nut provides continuity between the bolt and the numbered copper strip, as well as securing the copper strip. There's a hole just under the tapered end of the copper strip. A piece of wooden dowel pushes the end of the copper strip up and away from the edge of the steel plate that forms the ground bus. When you press a key, it lowers the dowel, allowing the copper strip to contact the ground bus. It seems an unnecessarily complicated system, but hey it was the very first, so we can cut the guy some slack.
https://i.imgur.com/9OUEsUN.jpg
Here is the keyboard structure I'm working with.
https://i.imgur.com/4RMIf2A.jpg
https://i.imgur.com/zKSNRPY.jpg
As you can see, pretty accurate. However, I'm having difficulty getting decent continuity between the resistor ladder, copper strips and ground bus, so we are experimenting with different fixes at the moment. I can let you know what they are as we perfect them

But this is a start, and I hope synth devotees will find subsequent pots of interest.
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Blue Hell · Posted: Fri Nov 18, 2022 4:04 pm Post subject:

Interesting!

Watched some youtubes on it .. like https://www.youtube.com/watch?v=hszVbAHMt_c - sackbut bluess .. there seem to not be many sound examples .. fragments here and there .. with this one using some different instruments too .. or so it seems (piano ..).

Too bad that the imgur images require a lot of scripting to be active before they can be seen .. maybe you are willing to post them here?

And the video inlined ::

Mark Hammer · Joined: Mar 05, 2017 Posts: 11 Location: Ottawa, Canada

Here is the replica I'm working on, a front view of the second-generation synth from LeCaine, (which was polyphonic), and finally the inside and full view of the original (which the "sackbut blues" was played on). Note that the keys on the original and replica are bevelled at the sides to permit sliding one's finger up and down, as well as being able to apply lateral pressure on the keyboard. There was a striking amount of expression control in this thing. It may have been crudely implemented, but I'm impressed that LeCaine was thinking about it so far back.

I spent most of today setting up the keyboard. The copper strips had to be individually bent to within a tiny gap with the ground bus, such that pressing the key allowed them to make contact with the bus. The use of springs as movable contacts in later-generation keyboards worked much better, but I guess 1945 was gonna 1945!

I have more pics if people are interested.

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Blue Hell · Posted: Fri Nov 18, 2022 5:33 pm Post subject:

Your replica is eh .. very much the same Smile

Thanks for explaining the key beveling ... I had been wondering already!

Meanwhile .. when you (one) need(s) to kill 1h 15min of time .. https://www.youtube.com/watch?v=S80VssmKb2E .. Hugh Le Caine - Compositions Demonstrations 1946-1974 .. featuring several early electronic music ideas ... the electronic sackbut .. for instance .. but many more ideas and some nice explanations here and there Exclamation

Mark Hammer · Joined: Mar 05, 2017 Posts: 11 Location: Ottawa, Canada

Sadly, while there are photos of him at the sackbut, and audio recordings of him playing it, there is no film of him playing it, nor is there a complete schematic of it. So some of the controls and what they are intended to do are not well understood. But it was very much an instrument oriented towards expression control, such as could be imagined in the late 1940s. t had portamento/glide, and the user would play the keys with the right hand and operate the expression controls with the left: one with the ring finger, another with the index, and the third with the thumb. The disc you see here was divided into quadrants which the user would/could rotate with their finger to alter the waveform.

While the aftertouch on the keyboard utilized a mechanical contact which had to be adjusted to leave a sort of hairline gap that added downward pressure could close, we'll be using force-sensing resistors. I have to emphasize I'm just a "hired hand" and not the brains or instigator behind the project. I'm just a huge fan and pleased to be associated with it.

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