The ring modulator guitar pedal instructions and schematics provided here make your guitar sound like a low-fi synthesizer. This circuit uses a standard guitar input to produce a modulated square wave output. It also includes a filter which helps to soften the signal a bit, and adds some resonance to make it sound more outer-spacy. This pedal is a fun and easy weekend project that could easily be customized to suit your aesthetic preferences.
Check out the video for a brief demo of how the pedal works. My playing doesn't do justice to the potential of this pedal.
To learn more about the parts used in this project check out the Electronics Class.
Step 1: Materials
Materials you will need include:
(x1) LMC567 tone decoder (see notes) *
(x1) TL071 op amp
(x2) 1N34A germanium diodes
(x1) 5mm red LED
(x2) 100K potentiometers
(x1) 50K potentiometer
(x1) 10K potentiometer
(x1) 1M resistor
(x8) 100K resistors
(x1) 10K resistor
(x1) 4.7K resistor
(x1) 100uF capacitor
(x1) 10uF capacitor
(x2) 0.1 uF capacitor
(x4) 0.01uF capacitor
(x1) 470pF capacitor
(x1) Heavy duty DPDT foot switch
(x1) 1/4" mono jack
(x1) 1/4" stereo jack
(x1) Hammond BB-sized enclosure
(x5) Self-adhesive Velcro pads
(x1) 9V battery connector (not pictured)
(x1) 9V battery (not pictured)
(x1) Circuit board (see below) ***
(x1) Decal (optional)
Tools you will need include:
(x1) Hand drill or drill press
(x1) 1/2 drill bit
(x1) 3/8 drill bit
(x1) 9/32 drill bit
(x1) 1/8 drill bit
(x1) Center punch
(x1) Electronics kit
(x1) Exacto knife
(x1) A computer printer (for the drill template)
* NOT THE LM567!!! There is a BIG difference in performance between the LM567 and the LMC567. The LM567 produces a constant tone even when not playing.
*** I had a few extra made, if you are interested in buying one, PM me (while supplies last).
Please note that some of the links on this page contain Amazon affiliate links. This does not change the price of any of the items for sale. However, I earn a small commission if you click on any of those links and buy anything. I reinvest this money into materials and tools for future projects. If you would like an alternate suggestion for a supplier of any of the parts, please let me know.
Step 2: About the Circuit
This circuit is based upon two of Tim Escobedo's circuit snippets which both have been modified slightly and combined together. The signal first passes through a ring modulator stage which is based on an LMC567. For all intents and purposes, this essentially turns the guitar signal into a square wave and make it sound like a robot. The robot-sounding signal then goes through an adjustable low pass filter based on a TL071 op amp. This adjustable filter serves to trim higher frequencies, add resonance, and makes the signal a little less harsh.
Step 3: Design and Print the PCB
Step 4: Assemble the Board
Next step is to assemble the PCB as specified in the schematic.
Don't worry at this moment about attaching all of the external components like the potentiometers, jacks, and switch. Wiring those correctly is going to happen in a few steps.
Step 5: Drill Mounting Holes
Drill mounting holes using the attached template.
If you have never done this before, I recommend checking out the DIY Guitar Pedal instructable for an in-depth example on the proper way to drill an enclosure using a guide.
Step 6: Registration Holes
Once the potentiometer mounting holes are drilled, the next step is to create smaller holes just left of each one for the potentiometer's registration tab. This prevents the potentiometer from spinning in place once mounted and also helps mount it flush to the enclosure.
The easiest way to mark where to drill is to insert the potentiometer into the hole upside down and backwards. Then, wiggle it back and forth until you create a marking.
Drill this marking with a 1/8" drill bit.
Step 7: Wire the Potentiometers
Attach green wires to the center and the right-hand pin for each of the potentiometers.
Attach a black wire to the left-hand pin on the 50K potentiometer and also one of the 100K potentiometers.
Finally, solder each potentiometer to the circuit board as appropriate (as specified by the schematic). Keep in min the center pin of the 50K volume potentiometer does not get soldered to the board. Instead, this will attach to the foot switch.
Step 8: Connect the Switch and Jacks
Speaking of the foot switch, now is time to wire it up.
Wire together one of the sets of outer pins on the switch.
Next, connect the signal tab from the mono jack to the center pin, and the signal tab from the stereo jack to the other center pin.
Connect the wire from the 50K potentiometer to the other set of outside pins such that it is in-line with the mono jack.
Finally, connect the remaining free outside connection to the audio input (IN+) on the circuit board.
Step 9: Attach the 9V Battery Snap
The stereo jack is going to serve as the power switch by making or breaking the ground connection when a mono plug is inserted.
Solder the ground connection from the 9V battery snap to the metal tab connected to the smaller signal prong.
Connect a black wire between the stereo jack's barrel jack solder tab and the ground input on the circuit board.
Step 10: Print the Decal (optional)
The decal is both for aesthetics and to hide the potentiometer mounting registration holes.
To print the decal I printed the sticker onto vinyl sheeting using a plotter printer, and then cut it out by hand.
This was a deviation from initial plan which was to cut out each color separately using a desktop vinyl cutter. This method should work just as well.
If you have neither a vinyl printer and/or cutter you can purchase sticker paper for your desktop printer and use that. Although, it might not look as finished or be as durable>
If you are feeling rich, you can just pay someone to make the decal for you.
If you are feeling poor, you can just skip this step.
Step 11: Apply the Decal
Carefully apply the decal to the enclosure.
Cut out the potentiometer mounting holes if necessary.
Step 12: Attach Velcro
Apply adhesive Velcro pads to the bottom of the circuit board and 9V battery. Then, stick both to the inside of the lid.
This serves both to hold everything in place, and insulate it from the metal enclosure.
Step 13: Case Closed
Once you have done that, close the case back up.
Step 14: Finishing Touches
The last thing to do is to mount the knobs to the potentiometer.
Once you have done that, you are ready to rock.
From left to right the knobs control modulation frequency, resonance, filter cutoff frequency and volume.
Shine on you crazy diamonds.