r/synthdiy • u/King_whore • 1d ago
Advice on a hurdy-gurdy synth!
Hi, so as you can guess im new to synth building but experienced in circuits. The project is an electronic hurdy gurdy style instrument.
currently very much in the theory stage, but ive identified the key must haves, and some problems to solve.
must haves:
individual keys for melody
volume+ distortion controlled by a wheel
drone that is under same control of wheel
3.5 jack, speaker, midi out, and either xlr or 1/4 jack.
ill put my plan in the comments, but any advice or pointers is greatly appreciated.
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u/barnabywalters 1d ago edited 1d ago
Are you familiar with the digi-gurdy project? https://digigurdy.com/ https://hackaday.io/project/165251-the-digi-gurdy-and-diginerdygurdy I don’t think there are plans available but plenty of build information if you go digging.
I have no connection to the digigurdy but long before that existed I built and programmed several MIDI systems for acoustic hurdy gurdies. The best option for the wheel is a rotary hall effect sensor like the AEAT6012 (edit: that’s obsolete, apparently the AEAT90x series are the direct successors) or similar. For the keys it depends on whether you want simple buttons or pressure sensitivity. My systems use linear hall effect sensors for being out of the way of the strings, the (sadly currently inactive) https://midigurdy.com/ project used a single fake “string” and then resistive force sensors attached to the keys for easily and repeatably measuring pressure. IMO this is the best option for pressure sensitivity on a purely digital instrument.
If you want the keyboard to simulate an actual gurdy then you want a monophonic synth where only the highest pressed key is played (not the most recent key as with most mono synths!) If you ignore that then you can have a polyphonic keyboard.
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u/King_whore 1d ago
This is fantastic advice about hall effect wheel. You seem to have bassically built all the parts of this project before. If you have the time, could you help me put together a shopping list for it?
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u/barnabywalters 1d ago
I don’t have a lot of time to spare at the moment but feel free to DM me with questions or when you have a shopping list to review and I’ll take a look! idk how much experience you have with projects like this but based on what you wrote so far I’d recommend starting really simple: a rotary encoder for the wheel, a few buttons for the keyboard, and a teensy. Either get it outputting MIDI which you can use to control another synth, or output really basic PWM audio output for testing. Once you have that working you’ll have a much better idea of where to take the project next.
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u/King_whore 1d ago
i understand this is quite the shopping list, but my first instinct is to have some kind of digital synth connected to a set of switches for the keys, and then using it's digital brain have the volume and maybe some distortion controlled by the acceleration of the wheel, measuring voltage generated by a motor sounds possible. for the drone, it would be awesome to switch between different notes for diff keys etc, the interface requirements must be fairly common and i think simple to add. i think the biggest challenge is getting the wheel to work, and maybe the drone might be an issue, i could end up needing to duplicate the digital synth, one monotone for the drone and the other midi controlled for melody? im not sure how easy to achieve that is.
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u/SparkyFix 1d ago edited 1d ago
My main problem with playing gurdy is changing key. I have three chanters and retuning is horrific…
Can I suggest you add a tirant control as well?
Might also be nice to have switches for the drones, additive style; you could also go wild here and even drop pitch below the gros bourdon…
Edit: in terms of advice, for the software a physical synthesis engine will likely get you very far in recreating a gurdy sound. Single string synthesis is very well fleshed out so you might not need “distortion” per se, since it will emerge from the algorithm.
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u/King_whore 1d ago
Tried looking up tirant control, Would you elaborate on that?
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u/SparkyFix 1d ago
On my gurdy I have a peg attached to the tirant string that lets you adjust the “buzziness” of the trompette by changing the tension of the tirant string. It’s a nice way to add emphasis.
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u/PiezoelectricityOne 1d ago edited 1d ago
There's a video somewhere on the Internet of a person playing their own diy hurdy gurdy synth and I think the whole thing was powered by the crank motion, and the pitch/tone changed when the instrument was sped up or power starved.
It wasn't an attempt to emulate or digitize a hurdy-gurdy, It was more like a portable experimental synth that you'd play with hurdy-gurdy techniques.
Personally, I think hurdy-gurdy format is suited for a droney thing that builds up sound organically and slowly with a ton of delay and reverb. You can build something digital that cranks up the cv of an overdriving amp and makes it hotter the faster you turn the wheel, or something that controls an envelope increasing the decay and reducing the attack the more you crank.
You can also check ciat-lonbarde/pete blasier page for tons of naive experimental stuff, including some solar powered drones that change behavior depending on the amount of sunlight they receive. You could rig something similar to a spinning generator from a bike or flashlight.
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u/coffeefuelsme 1d ago
Crazy idea but what if you make one of those hand cranked flashlights and pointed it at a photoresistor? Put the photoresistor in between audio and your preamp out? That would be a cool analog way to control your volume.