Lab # 14: Let's Build a LM386-based Guitar AmplifierGoal: To build, on a breadboard, a functional audio amplifier using the LM 386 IC chip.

Background:The LM386 is an integrated circuit that functions as a power amplifier. This

means that it can bring two signals together, one with an audio signal and one withpower, and output the amplified audio signal. The amplified output is described interms of gain, which is the ratio of input to output. The LC386 chips is capable ofproducing a gain of 200, meaning the output is 200 times the voltage of the inputfrom the pickup.

It is packaged in what is known as a dual in-line package, informally knownas a DIP chip. More specifically, this chips is a DIP-8 which means that it has 8 pinsprotruding from its sides, 4 on each side. This chip is suitable for battery powereddevices such as radios, MP3 players and guitar amplifiers. It will function over arange of input voltages from 4-12 volts, making a 9V battery an ideal power source.And it produces an output of .250-.325W, enough power to create a fairly loudamplifier.

LM386 MPF102

Basic Circuit: An amplifier circuit built using this chip with no other components buta speaker, a 9V battery and your Diddley-Bow signal will function but will producea rather harsh sound. For this reason, step-by-step we will incorporate several othercomponents to shape the sound in various ways.

Improvement #1: We will incorporate a preamp. Using a transistor as an amplifier,we will boost and "color" the sound with warmth before it goes into the LM386. Thetransistor we will use is called an MPF102. Technically, it is a JFET junction field-effect transistor but we will not go into the theory of this device - we will just use it.It has three pins, 1 2 and 3. 1 is the input from the 9V battery, 2 is the ouput tothe LM386 chip and 3 is the input from the audio signal (our Diddley-Bow).

Improvement #2: We will add a volume knob. We will do this by inserting apotentiometer and capacitor between the output (pin 2 of the MPF102) and theLM386.

Improvement #3: We will add a capacitor and a resistor in parallel before the signalgoes to the speaker. This makes a big improvement in sound quality and thefunctioning of the volume knob.

Materials:Quantity: Description1: Breadboard4: 4-6" jumper wires (2 to connect speaker and 2 to connect 1/4" jack for input signal) You will need to create other jumpers to connect pins 3, 4 and 6 of the LM386

1: LM386 chip 2: 220 µF capacitors (µF means microFarads, Farads are units of capacitance,µ means x10-6)

1: 10 µF capacitor 2: 47 nF capacitor (nano means x10-9) Serial number "2C473J"

1: MPF 102 transistor

1: 10Ω resistor

1: 3.3 kΩ resistor

1: 1/4" mono female audio jack

1: potentiometer10kΩ potentiometer

1: ground 2: output signal 3: input signal

1: 9V battery clip

9V battery

Output to LM386

Audio signal

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Instructions:This project will be graded according to how many levels you are able to build into thecircuit. A functioning basic circuit earns a 70%. Improvement #1 earns a 80%.Improvement #2 earns a 90%. Improvement #3 earns a 100%. All are attainable and Ireserve the right to make subjective decisions regarding the definition of "functional".

Basic Circuit includes the LM386 and a 220 µF capacitor between pins 1 and 2 (the longerlead should connect to pin 1) and another 220 µF capacitor between pin 5 and the speaker(the longer lead should connect to pin 5).

Improvement #1

Improvement #2

Improvement #3