Circuit: DIY Digital Multi-Effects Unit

In 2010, Elektor presented a digital multi-effects unit based on the FV-1 effects processor that was designed to provide musicians with 15 configurable sound effects like reverb, chorus, and flanger. The system featured a user-friendly interface with an LCD, MIDI input, and an EEPROM for storing custom effect algorithms, making it a versatile tool for music production. The circuit was built around an ATmega8 microcontroller, which handled effect selection, parameter adjustments, and digital potentiometer control.

Mult-Effects Unit Circuity

An ATmega microcontroller controlled the effects processor IC via four digital lines and three analog lines. The user interface had its own microcontroller.
  Hubert Bollig explained:

“It’s fairly easy to understand the operation of the circuitry on the main board. The audio signals from the input connectors are fed directly to the inputs of the FV-1 IC via coupling capacitors, and to the inputs of the buffer amplifiers for dry/effect mixing (IC1a and IC1b). The outputs of IC1a and IC1b are fed to the inputs of the electronic potentiometers (X9C503). The output signals of the effect processor are fed to the other inputs of the digital potentiometers. The signals from the potentiometers pass through buffer amplifiers on their way to the output connectors.”

Refer to the schematic of the main board, with the buffer amplifiers for the signal inputs and outputs and the digital potentiometers for dry/effect mixing shown on the left. The three resistor/capacitor networks in the middle of the diagram convert 5-V PWM signals into DC control voltages with a range of 0 to 3.3 V.
 

Key Features

The user-friendly design features the following:

• LCD
• An EEPROM for holding eight supplementary effect algorithms
• A ramp generator for attack and decay effects
• 64 preset profiles for user-defined effect settings
• A MIDI interface
 

Multi-Effects Unit Project

The article, “Digital Multi-Effect Unit,” appeared in Elektor September 2010. You can access the article free during the two weeks following the publication of this post. If you start your own project, share your progress on the Elektor Labs platform!

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Editor's Note: The article first appeared in a 2010 edition of ElektorMag. Some of the components, PCBs, products, and/or links might not be available any longer in the Elektor Store or elsewhere. Still, we feel this content is valuable, and we hope it will inspire you to start new working on new projects at your workbench.

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