Circuit Lake

The dsPIC33FJ64GP206-based Ultimate Tremolo is a DSP-based guitar effect pedal that gives the user complete control of every parameter of the tremolo (or amplitude modulation) audio processing effect. This is accomplished by interfacing the pedal to a PC via a Microchip PIC18F4455 USB-enabled microcontroller and editing the settings through software rather than the normal convention of making rough adjustments to the effect with a few knobs located on the pedal. This Tremolo does, however, also have knobs than can edit the traditional tremolo parameters of Depth (amount of modulation amplitude) and Rate (frequency of modulation) when a PC is not available.

The main feature of the project is its ability to let the user create custom low frequency oscillator (LFOs) waveforms to modulate the volume of the guitar signal. Amplitude drawing panel that lets the user create waveforms using drawing tools such as Line, Arc, and Freehand as well as Square, Sine, and Triangle wave tools. Another feature is its patch-saving capability. User can store setting to recreate the desired sound from the pedal. The pedal can store up to 25 patches on a 24LC512 I2C Serial EERPOM.

Kit Church, the project designer, said that this guitar effect processor also delivers exceptional sound quality. A Burr-Brown OPA4134 quad op-amp with only 0.00008% Total Harmonic Distortion (THD+N) is used to provide a guitar signal input buffer and low pass filtering. A high-performance Burr-Brown PCM3060 Stereo Codec provides A/D/A conversions with 24-bit resolution at a 96 kHz sampling rate. The ADC portion of the chip has a THD+N of -93 dB and a Signal to Noise Ratio (SNR) of 99 dB, while the DAC has a THD+N of -94 dB and SNR of 105 dB.

PIC Tremolo
Download Project Documentation (zip)
circuitcellar.com