The Tone Scratcher Presentation

8/12/2019 The Tone Scratcher Presentation

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EET402 Capstone Project

Dr. Ali Setoodehnia

Unit 1 Project Proposal

Dave Philpott

I pledge to support the Honor System of ECPI. I will refrain from any form of academic

dishonesty or deception, such as cheating or plagiarism. I am aware that as a member of the

academic community, it is my responsibility to turn in all suspected violators of the honor

code. I understand that any failure on my part to support the Honor System will be turned

over to a Judicial Review Board for determination. I will report to the Judicial Review

Board hearing if summoned.

2 December 2013

The Tone-Scratcher: A guitar distortion box



OUTLINE

I. Introduction

II. Project description

a. What the Tone-Scratcher is

b. What the Tone-Scratcher doesIII. How it is used

a. Applications

b. Operation

IV. Block diagram

a. Amplifier stage

b. Filter stage

V. Hardware

a. Parts usedb. Operation of components

VI. Parts list

VII. Construction breakdown

VIII. Summary



INTRODUCTION

When I’m not knee-deep in homework or chores around the house, I like to get on a stage and play m

pedals to change the raw sound of my guitars; some pedals add delay, some add chorus, and some ad

have always wanted to build my own effects pedals, and so for my project I built a distortion box.

This presentation shows a description of the distortion box and its applications. I have included a bloc

showing the stages of processing, and I break down how the stages work, showing waveforms of the a

addition, I list the parts used in the construction of the box, as well as details of the completed project



PROJECT DESCRIPTION

The Tone-Scratcher is a distortion pedal. It is a boxcontaining circuitry designed to alter an input audio signal

by distorting the signal’s waveform. Using a transistor,

capacitors, resistors, and diodes, the Tone-Scratcher clips

the peaks of the waveform, resulting in an audio output

that can be described as fuzzy or crunchy. It is used to give

an instrument, such as a guitar, tonal character. This type

of processor is typically placed on the floor and is foot-activated, hence the nickname “stomp box.”



HOW IT IS USED

• Instrument plugs into the box w

• Electronic circuitry alters the to

• The altered signal outputs to a

• The amount of processing is us

http://img.howcast.com/thumbnails/510112/1_basics_order_xxlarge.jpg



BLOCK DIAGRAM

• Two main processing stages are used

• Amplifier: increase or attenuate gain

• Filter: pass or block specific frequencies

• Both stages are adjustable for tonal variety



HOW IT WORKS: Amplifier Stage

• A transistor is used for amplification

• Wired with emitter-feedback bias

• Bias establishes the transistor’s linear

operation parameters

• A potentiometer drives the transistor into

saturation or cut-off, creating distortion



HOW IT WORKS: Amplifier Stage

• The top waveform is a 440

• Gain potentiometer is set a

•

The output signal is distort



HOW IT WORKS: Filter Stage

• Capacitors and resistors are configured in two

types of filter

• The high-pass filter blocks lower frequencies,

passes higher frequencies

• The low-pass filter blocks higher frequencies,

passes lower frequencies

• Signal is then clipped by diodes



HOW IT WORKS: Filter Stage

• The top waveform is a 440 H

• Filter potentiometer is set at

•

Signal goes through a diode

• The output signal is distorted



HARDWARE

The transistor is used to amplify the input signal.

provides dc bias for the operation of the transisto

are used to establish the bias. A potentiometer va

and can drive the operation in saturation, thus dis

signal.

Capacitors and resistors are arranged in either a h

low-pass filter circuit. A potentiometer sweeps be

filters to provide variance in the output tone. Dio

clip the filtered output signal further, adding to th

distorted tone. A final potentiometer affects the o

The circuit board is generic and required the circu

constructed on the board. Two stereo input jacks

an input and output for cabling. The switch toggle

clean (unprocessed) or distorted (processed) tone

houses the project.



PARTS LIST

Ca

(x1) 0.1u

(x1) 0.04

(x2) 0.01

Resistors

(x1) 2.2M ohm resistor

(x1) 33K ohm resistor(x1) 22 ohm resistor

(x1) 3.3K ohm resistor

(x1) 680 ohm resistor

Diodes

(x2) 1N4148 diodes(x2) 5mm LEDs

Transistors

(x1) 2N3904 NPN transistor

Misc

(x1) PC Bo

(x1) 9V ba(x1) 9V ba

(x3) Knob

(x2) Stere

(x1) BB pr

Wire

Switch



PROJECT CONSTRUCTION



SUMMARY

The Tone-Scratcher is an example of how electronic circuitry can be used in an atypical fashionart. For example, a transistor is usually biased so the amplification is linear and does not deform

signal at the output. In most cases, distortion is an undesirable result; here, distortion is the int

The difference between an artistic statement and noise is perhaps control over the output. The

variable resistors and known filter configurations provides such control, enabling the user to ad

away as much or as little distortion as desired.

Having built my first effects pedal, I am certainly encouraged to build more. The challenge is de

the correct configuration of components to achieve a specific effect. With the Tone-Scratcher I

succeeded in building a basic overdrive pedal, capable of adding a subtle amount of distortion or any other input signal.



REFERENCESAll photographs and diagrams are original property except

Slide 3:

http://img.howcast.com/thumbnails/510112/1_basics_order_xxlar

retrieved 25 November 2013.




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The Tone Scratcher Presentation