Controlling Guitar Amps With Servos

[fichl] plays electric guitar, and with that hobby comes an incredible amount of knob twisting and dial turning. This comes at a cost; he can’t change the settings on his small amp without taking his hands off the guitar. While larger, more expensive amps have multiple channels and footswitches, this tiny amp does not. Instead of upgrading, [fichl] came up with a device that turns his single channel amp into a completely programmable one, with just an Arduino and a handful of servos.

The amp in question – an Orange Dark Terror head – has just three knobs on the front of the chassis, volume, shape, and gain. [fichl] had the idea of controlling these knobs electronically, and the simplest solution he came up with is cheap hobby servos. These servos are mounted in an aluminum box, and mount to the knobs with a few shaft couplings.

The footswitch is the brains of the setup, with three buttons, four LEDs, and a DIN-5 output jack that delivers power, ground, and three PWM signals to the servo box. With the help of an Arduino Nano, [fichl] can change any of the knobs independently, or switch between twelve programmed settings. It’s an interesting setup, and something that could serve as a prototype for a much larger system on a much larger amp.

26 thoughts on “Controlling Guitar Amps With Servos

    1. Thanks!
      The metronome is triggered by holding down the right button and pressing the left one.
      It will blink the 4 LEDs (green,red,red,red)…
      The speed can be controlled with the middle (-) and the right button (+).
      Left button will exit metronome.

      Thanks again to hackaday for publishing this.

  1. This is neat, but why not just run it all through a laptop using software VST’s and a midi footpedal? Heck you can even run your whole band through reaper live and give them 100 effects pedals each.

    1. Why not run it through a tin can and use twine to propagate the sound!!?!

      Simply stated, you must not know much about Orange amps – but more specifically, VSTs are VSTs, hardware is hardware. They are not the same.

    2. Processing delays gets prohibitively long when you couple so many systems into a single computer.

      It gets annoying if there’s a 100 millisecond lag between pressing the key and sound coming out of the speakers.

  2. With lithium power and small onboard effects, just get rid of the effect laden small amp. Play into a fully able sound system with 2 or more channels. It’s time the electric guitar get electric not just a passive coil pickup.

    1. Also, there are far more variable resistors in your car than you think.
      Unless you have a car that was made before the last two decades, there’s going to be digital control modules in there already.

    2. Fuel gauge sender, brake pedal position, instrument lamp dimmer, throttle position (my car has two of these), climate control knobs, etc. Pots are everywhere in a car, whether old or new.

    1. Cannot tell if joking, but.. Servo amplifier is a industrial motor control product. Servo in an amplifier is another way to say feedback. There are two terms shortened to ‘servo’.. Servomotor and servomechanism

    2. I think you are referring to servo topology, which can be used for direct coupling or compensate for devices that would require matched pairs. These are simple servo motors, which allow positioning. A solid state device has a tendency to vary in conductance with temperature. Self bias can compensate for this, but requires coupling capacitors to block DC offset from affecting the next stage. A servo circuit can be used to control the drift that occurs, so that the coupling capacitor can be eliminated to allow better low frequency response and/or improve phase response.

    1. True – my concern would be with the motors somehow coupling with the audio. Appropriate filtering on the motors and the motor PSU might be all it takes to battle that I suppose.

  3. I made such a system several years back with the intent on going commercial with it but I lost the motivation past the prototype stage. Finding suitable servos that not only had sufficient rotation but also speed was a challenge. I contacted a few chinese manufacturers to customize some of their servos but they weren’t particularly interested. I did hack a few of the samples they sent me which did increase the rotation rate which had the added benefit of reducing the torque (didn’t want them breaking something if the user didn’t calibrate the controller right) but wasn’t something I personally wanted to do for each part. It was a simple one gear modification but I lacked the business skills and funds to convince the suppliers to build them. I’m happy that others are building such controllers, especially since I let the project linger, but also a bit saddened that I never made it a commercial reality and have now been beaten to the punch.

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