Hackaday Prize Entry: DIY Guitar Multieffects

Guitar effects and other musical circuits are a great introduction to electronics. There’s a reason for this: with audio circuits you’re dealing with analog signals and not just the ones and zeros of blinking a LED. Add in the DSP aspects of audio effects, and you have several classes of an EE degree wrapped up in one project.

For his Hackaday Prize entry, [randy.day] is building a guitar multieffect. Instead of just a single distortion, fuzz, or chorus circuit, this tiny little PCB is going to have several flavors of pitch shifting, a flanger, chorus, echo, harmony, and stranger ‘digital-ish’ effects like bitcrushing.

This effects unit is built around a PIC32 and a TI audio codec which processes the audio at 64k 32-bit samples/second. This takes care of all the audio processing, but the hard work for a guitar pedal is actually the enclosure and mechanicals – it’s a hard life for stage equipment. For the foot pedal input, [randy] is using a magnetic position sensor, but there’s no word if he’ll be using a fancy die-cast enclosure or a plastic injection molded unit.

The 2015 Hackaday Prize is sponsored by:

14 thoughts on “Hackaday Prize Entry: DIY Guitar Multieffects

  1. I like the idea of putting it right into the guitar body instead of an enclosure. You can only use it with one guitar, but that guitar would have tight integration. Even add a second jack out of the guitar, that is the processed signal (or via a switch), that could go right to a PA.

    1. Me too, just imagine a bass guitar with a electronic tremolo, but even more: instead of the pedal use the tremolo bar hocked on your sensor. What it does miss, at this moment is a (auto) tuner function (with dc motor drive, 5V 500mA for driving a servo per string), perhaps also a ws2882 rgb LED output channel. Also a headphone output would be nice, but an important thing: put a buck convert inside so you could feed (almost Li,9V, Phantom Supply) any voltage to power the board.

      1. Servos and auto-tuning are a bit beyond me at the moment. WS2812 is out, since the TI chip gets priority on timing; if anyone knows of an rgb LED that uses SPI, I could look into that. Did you have an idea for a feature that uses an LED, or would it just be a blinkey light?
        I considered a buck/boost, but I wasn’t sure if the extra cost was worth it. It would have to provide 3.3v and 7.2v.

        1. I was thinking for an alternate display/indicator, like for tuning or fx-settings, specially when it’s mounted inside a guitar, auto tuning is simple if you already got the normal tuner (frequency counter) code, perhaps driving an additional board via spi (send string number, up or down).

          1. Ah. Interesting. I could have it glow blue for flat, green for tuned, red for sharp. It might even be easier to see at a distance (i.e. foot pedal on the ground) than the words ‘flat/tuned/sharp’ on the display.

      1. The output jack is stereo; currently, the extra channel adds the selected effect to an Aux In signal (i.e. mic input) – imagine pitch-shifting the voice along with the guitar.

        I do like the idea of layering two effects on separate channels. It may not be possible to combine the more algorithmically-intense effects this way – there are only so many clock cycles between samples – but it is something to look into.

  2. I am totally into the integrated guitar. Mine just came back home after our summer monthly Main Street party. It’s a two string steel with everything from the lithium battery to a hotspot style speaker on board. Digitech FX and the self sustaining driver feedback. There is only one speaker but stereo line out is there, transformer coupled for no hum loops or bucking-whine.

  3. Just wanted to add my dad has had the same old play worn hagstom 6 string since ’68. At this point over the years he build, added modded and removed about every analog effect known to man that the pick guard on the thing looks like swiss cheese.

    Pretty epic that I grew up around this exact kind of hacking in the 80’s.

  4. I constantly get requests from my guitar friends to cram this or that pedal into the guitar. I have been sending them to the kaoss pad 2 mini to keep everything stock and make everyone happy, but I really like your project Randy. I will have to follow it and kudos on all of the hard work. I am not too far into the effects end of it and have only built a phaser and ring modulator for my personal use and enjoy them so maybe it is time to pick it up again. Best to you and keep on making music :)

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