Sinfonion -> Teletype Bridge

Here’s a little something I’ve been working on that might be useful to the very small subset of people that have both a Teletype and a Sinfonion. One of the biggest issues with the Sinfonion is that it is so fantastic you end up wanting to use it for all your voices… including your other synths over midi. The Teletype is also, of course, an extremely powerful sequence and quantiser. Wouldn’t it be great if they played together?

Unfortunately the Sinfonion doesn’t have implemented i2c. However! It does have a feature called harmonic sync that’s designed to allow two Sinfonions to play together.

Mathias (Der Mann mit det Maschine), the creator of Sinfonion, kindly shared some code to allow me to reverse engineer how the data stream of the harmonic sync feature works.

I’m not a hardware person and I don’t have the means to design a separate module, so I’ve piggybacked off @attowatt’s excellent i2c2midi module.

Sinfonion → Teletype Bridge

Sinfonion → Teletype Bridge is a mod for the i2c2midi module. It includes custom firmware for both the i2c2midi and Teletype that includes a new OP to read the current Scale, Mode, Degree and Transposition currently in use on an ACL Sinfonion. It can be used to quantise note values on the Teletype to the currently selected key of the Sinfonion. This essentially extends the number of Sinfonion’s quantiser channels by as many CV outs as your Teletype setup has. As well as this, it allows you to send Sinfonion-quantised notes to midi devices via the i2c2midi.

(sorry about the production values, or lack of, on this video).

The Mod

To get this to work, you need to solder an extra TS Jack to pin 7 (tip) and Ground (sleeve) on the i2c2midi’s Teensie. Make sure you have a 47K resister on the pin 7 wire. I put this new jack on a passive mult to expose the connection.

Then you need to flash your teletype with the Sinfonion bridge teletype custom firmware.

Next flash your i2c2midi with the i2c2midi Sinfonion bridge i2c2midi custom firmware.

Set your Sinfonion’s OUT 1 to Sync Master, then connect OUT 1 to your new i2c2midi jack.

That’s it! You can now quantise notes to the Sinfonion’s key using the new I2M.S.QT OP.


This is a really cool project! I’ve always wanted to be able to integrate my Teletype and Sinfonion better. It would be amazing if there were a version where the jack was integrated into the i2c2midi front panel. It seems like there’s plenty of panel real estate, but I don’t know enough about PCB design to know how tricky it would be to revise the current PCB for that.

Also - any thoughts on the feasibility of inverting the direction of the sync, and having Teletype control the scales on Sinfonion?

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It would be fairly trivial to modify the i2c2midi pcb and faceplate I assume. The issue is, of course, that the usecase probably doesn’t warrant the change on it’s own - I expect there wouldn’t be enough demand to do so unless the extra jacks had some sort of dual purpose (and this depends on other use cases for using a serial pin on the teensie - I’m not sure what those would be).

Luckily the mod is trivial with some really basic soldering skills and passive mults are a good home for exposing jacks. I used a bafaco coloured nut to denote the sinfonion in jack.

On syncing the sinfonion to the teletype - that’s an interesting idea. The serial data stream used on the Sinfonion contains some extra data that isn’t currently used in the teletype bridge implementation that would need to be reconstructed - clock, amongst other things. I’m not sure how difficult that would be. In theory, once the data has been constructed, it should be possible to use the same jack as in the mod above to transmit with teletype as leader and sinfonion as follower. The issue is that the UX wouldn’t be great. Mode and degree on the sinfonion are represented as arbitrary numbers. How would you set a specific scale on the sinfonion from the teletype? You’d need a table of scale names or something similar. This could work, but would require some careful design to make not clunky.

Given the sinfonion has simpler ways to control what scale and degree are selected outside of the harmonic sync function (the cv ins can be set to select the step, or even degree, for example), it doesn’t seem worth the effort (to me at least). Some custom teletype helpers to use those other cv options might be useful though.

I’ll give it some thought though. I might be missing a killer usecase. Suggestions are of course welcome too.

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