Electric Guitar Multi-FX

Electric Guitar

• • •  Distortion / Tremolo / Auto-Wah Effects  • • •  Digital Routing/Chaining  • • •   Save/Restore all Settings & Presets • • •  Microcontroller based  • • •  


Michael Vogel

Introduction

 

As a fourth-year requirement for my undergraduate engineering program at SFU, we spend a semester creating a unique hardware/software electronics product of our choice.

I combined my love of playing music (especially electric guitar) with my studies in electronics engineering to create a multi-effect unit for electric guitar. My group and I designed all hardware and software, built all circuitry and inventoried all components.

Our product includes three analogue guitar effects. Users can create a live queue, or “playlist”, of effects and effect presets, enabling them to cycle through presets in a live environment. As a guitar player, my rationale is that users can freely experiment with different effect combinations without having to change a single cable or turn a single knob.

 

 

Product Functionality


Three main effect categories:

  • Distortion, Tremolo, Auto-Wah
  • User can adjust, save, and restore effect settings/parameters (8 parameters in total)
  • Microcontroller controls digital potentiometer settings (settings are saved when device is powered off)
  • Each effect is built into single module (circuit board)

 

Effect Routing:

  • Any permutation of effect ordering is possible (16 in total)
  • Analogue multiplexers route signal depending on user configuration
  • Bypass foot-switches allow the user to creatively experiment with the sequence in real-time

 

User Interface:

  • Optical rotary encoder, buttons, LED displays, LCD screen and four footswitches comprise the user interface
  • Users can recall any saved effect parameters and saved routing, and cycle through presets in real-time using a footswitch
  • 7 segment LED display shows current effect sequence; additional LED indicates whether effect is “primed”

 

 

Diagram of User Interface

D: Distortion menu
T: Tremolo menu
W: Auto-Wah menu
Y: Yes/OK/Enter
N: No/Cancel/Back

 

 

 

Using the Product 

 
While the device does come with initial “factory” presets users have the ability to create their own effect sequences. 
To create a new preset the user navigates a shallow menu system using the button pad:
 

  • Select the first effect in the chain (Distortion, Tremolo, Wah)

  • Using the rotary encoder/knob, the user has the ability to adjust up to three effect parameters (e.g. gain and depth)

  • Select the next effect in the chain and repeat the process

  • Once finished, the new preset is saved and the user will be able to recall that preset even after power-off.

 

Any effect combination is possible, and not all effects need to be simultaneously activated. Footswitches activate the effects and presets, and intuitive buttons control the parameters of each effect and also control the user interface. The user does not need to rely on presets, however. The system functions in real time and the user can change the system settings at any time.

All features of the device are user-programmable. The user can store predefined effect sequences, and then retrieve any saved preset while still playing. Each of the three built-in effects (distortion, tremolo and auto-wah) can be fine tuned by the user, meaning a wide range of different sounds is possible within each effect type. The individual settings can be saved as presets and can be retrieved in a live setting.

The present effect sequence and current status of each effect (e.g. on/off) is visible above each effect footswitch, allowing for clear identification of the current settings. An LCD shows settings and presets.

 

We designed analogue circuitry to create Distortion, Tremolo and Auto-Wah effects.

 

Circuit Boards for the Three Effects

 

 

Partial photograph of the electronics inside the case.

 

 

Power and Digital Electronics
 

The Multi-FX device uses three voltage levels, 10V, -10V, and 5V DC to power all of its components. In order for all electrical components to operate as expected, the internal power supply of the device will use voltage regulators to ensure that each component is powered by a consistent voltage.

The operational amplifiers and the multiplexers are powered by +/-10 V.

All digital components require 5V to operate. Digital components include a PIC microcontroller, digital otentiometers, shift registers, inverters, and decoders.

 

Block diagram of high level digital circuitry

 

A PIC Microcontroller serves as the “brain” of the device. An interactive menu with an LCD display allows the user to easily modify all effect parameters, save presets and change the processing order of effects.

PIC Microcontroller in the Multi-FX Device

 

Microcontroller Specifications:

  • Microchip PIC18F4520
  • 40 Pin
  • 10 MIPS
  • 32KB Flash
  • 1.5KB RAM
  • 256B Eeprom

 

Diagram of Power Supply and Multiplexer/Switching Circuitry

 

 

 

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  1. johan
    January 19, 2013 at 11:50 am

    Hi All,
    Is it possible to direct me to any info on multi effects potentiometer ie. Wiring diagrams, circuitry and home build units. I am busy with a project and would gladly use any info containing usefull hints and leads.
    I thank you.
    Jvanderness

    • January 21, 2013 at 7:58 am

      Probably your best bet is to look up a beginner schematic for a distortion pedal (there are quite a few hobby sites devoted to this). Something that uses op-amps with feedback diodes would likely be the easiest way to get started. I haven’t had a chance to post my own schematics yet from this project, but stay tuned.

  2. August 31, 2016 at 10:18 am

    Excellent site. A lot of helpful information here. I’m sending it to several pals ans additionally sharing in delicious. And naturally, thank you on your sweat!

  1. September 13, 2009 at 1:55 pm
  2. September 15, 2009 at 3:59 pm

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