[sdiy] Magnetic String Actuation

Mike Bryant mbryant at futurehorizons.com
Thu Sep 8 16:59:03 CEST 2022

Where are you positioning and setting the angle of your electromagnet with regard to the strings ?
For example pushing large amounts of energy into an anti-node is probably not going to do anything.

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Spiros Makris via Synth-diy
Sent: 08 September 2022 15:02
To: brianw
Cc: synth-diy mailing list
Subject: Re: [sdiy] Magnetic String Actuation

thanks for all your suggestions! I started writing a response to everyone in the morning, but eventually got some supplies before hitting send, so scrap that.
So I went on and got a spool of 0.3mm diameter enamel wire and went on to make an electromagnet with about 500 turns on around a metal screw.
Came out 8ohms and 2.2mH. My amplifier module can drive up to 24W into this little thing but starts cutting off after maybe 1-2kHz. Turns out 0.3mm is pretty thin, anything above 0.5W makes it warm up. I even got some fumes out of it!
I can hear the coil vibrate and my instrument's pickups listen to whatever the coil is putting out (it's pretty loud if you point it towards the pickup), but I can hardly get any sympathetic action. I *think* I got a very slight vibration after fiddling around with it, but I'm definitely not even close yet.
I'm not sure what I should try next? Maybe I need more turns (inductance) to produce a stronger force? Could the coils' frequency response be way off and that's causing problems?

On Thu, 8 Sept 2022 at 07:03, brianw <brianw at audiobanshee.com<mailto:brianw at audiobanshee.com>> wrote:
Besides the fairly modern Sustainiac, there is also the vintage Roland GR-500 Guitar Synth. You could turn up the Release knob on the synth control panel, and magnetic actuation would keep the string(s) sustaining. I've never experienced this first hand, so I can't comment on how effective it was, but Roland has a US Patent on it.

Even newer than the Sustainiac is the modular "cycfi research" family of products and systems. I think this is your best bet, according to what my friends are saying. Again, I haven't worked with these products yet.


Brian Willoughby

On Sep 7, 2022, at 11:20 AM, Mr&MrsAccount <hbissell at wowway.com<mailto:hbissell at wowway.com>> wrote:
> There is a commercial product called "sustainiac" which is in the form factor of a guitar pickup. For starters I'd play with just a single string and then refine it from there.
> Harry
> From: Spiros <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
> To: synth-diy <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
> Date: Wednesday, 7 September 2022 2:02 PM EDT
> Subject: [sdiy] Magnetic String Actuation
> Hello, list,
> I am interested in experimenting with magnetic string actuation. That is, use an electromagnet to induce vibration to metallic(?) strings; the opposite of what a guitar pickup does typically. I have seen this concept realised in a couple of different applications:
> 1. Magnetic Resonator Piano is an electronically augmented piano that can do cool stuff such as real crescendos, electromagnetically dump strings, produce overtones etc. Every sound produced comes from the strings themselves.
> 2. Ebow is an electromagnetic actuator for the electric guitar. Place it close to the strings and they will start vibrating, similar to the way they do when using a bow.
> 3. Moog Guitar contains some sort of actuator and suitable circuitry to make it infinitely sustain notes, apply active damping and more.
> I bet there are more if we start digging, but these are some examples I can think of off the top of my head. Unfortunately, I don't have enough to go on here and decide on what kind of hardware I need to produce this effect. The magnetic resonator piano researchers have published a couple of papers that go over the fundamental equations involved. Still, unless you can really wrap your head around them (I can't) it's not enough to get you going.
> I obviously need some electromagnet, either off the shelf or custom wound. Then I need an amplifier that can drive enough power into it, in the correct frequency range.
> Aliexpress is full of various electromagnets. How could I decide on a couple that might be promising and give them a try?
> What about output amplifiers? I know the basics of driving speaker coils, but my guess is a strongly inductive load like an electromagnet is going to be a different story.
> I've been thinking about this for the past 10 years and still didn't manage to figure it out. Any kind of info or advice you could share is invaluable!

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