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New Project: Optical Tremolo Box

Plug your guitar (or axe of choice) into light-programmable waveforms with this unique effects box!

New Project: Optical Tremolo Box

MAKE contributing editor Charles Platt proposed a “Hypothetical Tremolo Wheel” in his article about online DIY guitar stomp-box communities (MAKE Volume 15, page 82, “Stomp Box Basics: Tremolo and Fuzz”).

Well, it’s hypothetical no more. I took Charles’ cue and built this Optical Tremolo Box, which reads a patterned disk with a light sensor to create a warbling volume effect (tremolo) that you can custom-program with any pattern you like.

How does tremolo work? So there’s your electric guitar, and there’s the amplifier it’s plugged into, and there’s the cable that runs between them. Open up that cable and you’ll find 2 wires — one “ground” and one held at a positive voltage relative to “ground.” The changing electrical potential between these 2 wires, over time, is what carries the sound signal.

What happens if you short-circuit those wires, bridging them with a third wire? The sound goes away. The charge can find its way home now, via the short, without ever bothering to go all the way through your amplifier. And so it does.

What if you bridge the 2 wires with a resistor instead? With a strong resistor, nothing happens — it’s still easier for the charge to go through the amp. With a really weak resistor, the sound cuts out. With a resistor in the middle range, the sound will be quieted, but not completely muted, as the charge divides itself between short and signal pathways. Use a variable resistor, and you have a crude volume control: turn the resistance way up, the sound will be loud; turn it way down, the sound will vanish.

And here’s where Charles had a clever idea: use a resistor that responds to light. Wave your hand in front of the photoresistor, and the volume will respond to the shadow of your hand. Mount a spinning disk with alternating clear and opaque bands in front of it, and the volume will follow the pattern on the disk, repeating as it spins. That’s tremolo — a repeating variation in volume over time.

Intrigued? Want to try building one? I thought you might. Let’s get started.

Sean Michael Ragan

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

  • ardian

    Nice idea, but then who’s gonna play the guitar?

  • Sean Michael Ragan

    You’re absolutely right, Nick, but I can at least tell you why it’s not. Basically, I wimped out of including a pulse-width modulation (PWM) motor speed controller in this design and opted instead for a simple series rheostat in-line with the motor. You can only get away with regulating DC motor speed this way when the motor is very low-powered. If you were to do the same thing with a 9V motor the rheostat would get much too hot. Version 2 of the box will definitely include a proper PWM motor speed control circuit; here’s a simple one based on a 555 timer, for instance:

    Another nice feature of using a 9V motor would be that it’s easy to find them with mounting holes in the case that are actually threaded, so you could use machine screws instead of wood screws to mount one in the project box.

  • Scott

    David, i bet radio shack would have most of these items, if not all.


  • Todd Birdsong

    The terminal strip can get kinda sketchy when you start wiring things up. If you think you didn’t keep good track of what wire went to what terminal, you may have misconnected something. Check the switch wires first, then the motor wires.

    • Tyler Pierro

      Is there any way to wire the tremolo box up with an SPDT push-button switch rather than a DPDT toggle?

  • Todd Birdsong

    I spent around $75 for eveything but solder and the iron.

  • Todd Birdsong

    I cut out six 3/16″ plexi discs today and mounted one to the motor shaft. The extra weight really makes a difference in terms of motor speed and centripetal force. If the disc is not placed exactly in the center of the shaft, the off-center rotation causes the entire device to vibrate and “walk” at its top speed. I might have to use something thinner, but with some rigidness for durability. (although it might be simpler to use a small case to protect the transperancy discs) Just another experiment…

  • Todd Birdsong

    Ok. I figured out my problem with the noise. I was using adhesive label material for the disc patterns and sticking them to 3/16 plexi. The adhesive material was too opaque for the LED to completely penetrate, causing the photoresistor to register the level of noise. I’ll stick with the transparency film for a clean sound.

  • Allan Rosner

    Did you figure out the wiring on your unit because i’m having the same problem. what did you do?

  • Sean Michael Ragan

    Apologies, this was supposed to have been linked from the parts list, but it looks that link isn’t working correctly. The hub is from Pololu:

  • Sean Michael Ragan

    Yes, it looks like RS stopped carrying this LED flashlight shortly after this project published. It is available from Amazon, however, in both the silver color used in this build

    And a black model that I wish I’d known about first!

  • Sean Michael Ragan

    It worked for me just now. If you still have problems, e-mail me at and I can e-mail you a copy.

  • Allan Rosner

    Hi Dan did you ever got the motor to work? Im having to same problem. If so let me know
    Thanks Allan

    • Gavin

      yeah i had the same problem too but i realized that somethimes the moter terminals get messed up and wont work if not in a certian position. try using tape to hold the terminal in the right position

  • Sean Michael Ragan

    Hey Allan,

    I know that you and some other folks are waiting on a schematic. It’s coming, I promise, and I appreciate your patience. We are in the process of getting our next special issue of MAKE wrapped up and sent off to the printers and I have just no time at the moment. Bear with me. It’s coming.

    In the meantime, you or anyone else who is having problems should feel free to e-mail me directly at Pictures of your build will be helpful if you can provide them.

  • Sean Michael Ragan

    Yes, you can use a modded pot. The only important thing is that it be on the order of 25-50 Ohms max resistance.

  • Sean Michael Ragan

    Verify that the plastic disk is not scraping against the metal phototransistor holder when it rotates. I have observed that phenomenon in my prototype, and think it is due to static charge accumulating when the plastic rubs against the metal. The charge builds up, and periodically discharges into the audio line, resulting in the click. Let me know if that does not fix it.

  • Sean Michael Ragan

    No. But it would definitely be better if it did.

  • Havok

    What Soldering iron are you using at the “Mount the rheostat” picture ?

  • Asbjørn

    I’ve never builded anything before but I really want to do this build because I’m a passionate guitarist. My problem is that I live in Denmark and as far as I can see, RadioShack doesn’t deliver in this area. Is it possible that you could link some pages where you can buy the components?
    Another thing is, do you need to use the specific ohm- and watt-parameters as shown? Or is it possible to use a resistor in 25 ohm with 50 watt instead of the rheostat 25 ohm and 3 watt?
    Sorry if my questions sound nooby, but I ain’t use to do this kinda stuff ;)

    I wanna do this build so much, so any help would be appreciated.

    • Sean Ragan

      Hello! Thanks for writing to us. Mouser Electronics should be a pretty good source for you:

      None of the parts used in this project is terribly specialized, should’t be too hard to find identical or equivalent bits through Mouser! Sean Michael Ragan Technical & Toolbox Editor MAKE Magazine

      • Asbjørn

        Okay – i figured out a solution for the RadioShack-problem. I have one other question (and sorry if it sounds noobie): I’ve just bought a 250V/15A Terimal Strip. Is that durable for these electronics?


        • Sean Ragan

          Yes indeed!

  • aj

    I cant get the links for the printouts to work. its not clickable… already bought the things but no luck with the links.

    • brocallmeaj04

      never mind was clicking on the wrong links… the highlighted ones in the instructions confused me.

  • brocallmeaj04

    I may have discovered a cheaper alternative to the mounting hub…was going to order but wih my foreign visa card its a pain. I had a rc heli that i hadnt used in a long while and took apart a few days before wanting to try this product for whatever parts i could savage. It just so happens that the gears connected to a rod was a perfect fit for the motor i was using. fit snug and pretty much circular so i plan on testing that out as my “mounting hub”.

  • Asbjørn

    I’ve got another question:
    Why is it necessary to tin the stripped wire when attaching it to the switch? Why can’t you just screw the wire directly to the switch? Would the connection be bad by doing so?

    Thank you!

    • Sean Michael Ragan

      Good question, because it’s really not necessary to tin the stripped wire. The connection should be fine either way. Tinning may help preserve the end of the wire over time better, but that is a small concern. If I were building this box again today, I would use soldered connections to the switch terminals, rather than screwed. At the time I tried to keep soldered connections to a minimum because I know the process of soldering can be intimidating. The drawback of using screws, of course, is that they can work loose over time.

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    […] tremolo wheel. Years later MAKE Technical Editor Sean Ragan would build this project, giving us the Optical Tremolo Box (and subsequently one of our most popular videos of all time, approaching 2 million views at the […]

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  • Paul O’Hagan

    Rather than the oversized easly knocked out of allignement goose neck LED I used an old laser mouse mounted inside the box with a hole drilled to let the laser light out (and back in) under the disc. Using a blacked out disc with reflective strips of foil tape, e.g. reflective side down. took a while to swap things around, find the right feeds in the mouse curcitry etc. I took a small pre amp from an ancient radio to boost the resultant signal, uses very little power as when the disc stops spinning the mouse goes into fallback mode and cuts most of the power to the laser. I suppose with a little effort one could use this to switch the whole box into a sort of stand by mode. Results…well i never did it your original way but i say it passes, kept me out of trouble for a few hours anyways :-)

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