Competency

Build an amplifier.

Design Challenge

• Connect the amplifier to the speaker constructed in the previous lab.
• Then evaluate the amplifier and compare it to a commercial amplifier.

Resources

• Operational Amplifier (Op Amp)
• Transistors
• Resistors
• Breadboard and Jumper Wires

Introduction

A commercial amplifier was used to operate the speaker constructed in the previous lab. This lab provides an introduction to electronics. You will have the opportunity to construct your own personal amplifier in this lab. Here is a link to a video with a preview:   https://tinyurl.com/opampvideo

A. Basic Information

1. Dawn of the Electronic Age

2. Components of a Music System

3. Origins of the Concept of Ground

4. An Introduction to Resistors

5. An Introduction to Breadboards for Prototyping Circuits

B. Applied Information

6. A Basic Op Amp Circuit

7. Building the Basic Op Amp Circuit

8. Testing the Basic Op Amp Circuit

9. An Introduction to Transistors

10. Enhancing the Basic Circuit with Power Transistors

C. Next Steps

11. Evaluating the Completed Amplifier

12. Designing a Prototype Circuit Board

The basic information in Sections 1-5 provides the theoretical information and background needed to understand how an amplifier works. The applied information in Sections 6-10 provides step-by-step instructions for constructing a basic amplifier.

We recommend the following approach to using this information:

1. First, skim the information in Sections 1 – 5 to get a sense of what is in each section.
2. Follow the step-by-step instructions to build the basic op amplifier. Refer to the basic background information as needed as you build the amplifier.
3. Once the basic amplifier is tested and working, read the background information more carefully to fill in theoretical gaps and consolidate your understanding.
4. Then follow the step-by-step instructions to build the enhanced circuit with power transistors.
5. Evaluate the final circuit and develop a frequency response curve comparing its input and output.
6. The final section on designing a circuit board (Section 12) is optional.

Lab Report

Write a lab report reflecting on the experience. What problems did you encounter with: (a) the instructions or (b) the construction process? What problem-solving strategies did you employ to resolve difficulties that you experienced?

Include the following information in the form of tables with recorded data and accompanying frequency response graphs similar to the sample tables and graphs provided in the documentation (in Section 5) accompanying this lab:

1. Frequency Response Curves comparing the input and the output of the amplifier that you constructed.

2. Frequency Response Curves comparing use of the amplifier with the paper speaker that you fabricated with the output of the second speaker with a wooden case

Also provide thoughts about ways in which this lab, piloted for the first time in this class, might be refined or improved.

Basic Amplifier Circuit for the LM714 Op Amp

Note: Pin 1 on the op amp is indicated by a small circular depression above that pin.

1. Power Supply
   1. Pin 7 is connected to positive voltage (+9V).
   2. Pin 4 is connected to negative voltage (-9V).
2. Ground: Pin 3 is connected to ground.
3. Feedback Resistor: The feedback resistor connects Pin 2 to Pin 6.
4. Input (Music Source)
   1. One input from the music player is connected to ground.
   2. The other input from the music player is connected to the input resistor (brown-black-red).
   3. The second lead of the input resistor is connected to Pin 2 of the op amp.
5. Output (Speaker)
   1. One lead from the speaker is connected to Pin 6 of the op amp.
   2. The other lead of the speaker is connected to ground.

Appendix: Basic Amplifier Circuits