The purpose of this lab was not only to use the breadboard to prototype a somewhat
complex circuit, but also to examine the physical attributes of amplification, revisit the
idea of electrical impedance, and explore the concept of frequency response, or the idea
of a natural filter. The idea of Thevenin equivalency was also revisited from Lab #3. The
concept of gain was introduced in describing what an amplifier does, and the process of
construction for a Bode plot was explored using Microsoft Excel. Also the idea of using a
logarithmic scale to represent gain was introduced, using a unit of decibels, or dB.
In electrical systems, it is often necessary to amplify extremely weak signals. Most
common in audio electronics, an amplifier is a device that does exactly that. Used
frequently with electric musical instruments, an amplifier is a necessity for any non-
acoustic musician. Specific to this lab, an extremely weak signal was produced by the
function generator. This signal was so small that, if hooked up directly to either a speaker
or an oscilloscope, the signal would most likely not produce any noticeable change. The
signal would move the speaker, but not strongly enough for it to produce a sound wave
loud enough to be heard by human ears.
With the concept of amplification come several other important audio concepts, such
as gain. Gain is defined as the ability of a circuit to increase the amplitude of a signal.
Gain is defined physically as the ratio of the output voltage to the input voltage.
mathematically, is shown as
. These voltages must be AC signals, as a DC
voltage will not produce a sound wave in a speaker.
In many audio-related systems, this gain is not rated linearly, as it becomes difficult
to see what is happening in a system graphically once the value of the gain approaches 0.
For this reason, the unit of decibels, or dB, is used. In order to find the gain in decibels,
one simply needs to find the gain in volts/volts and taking the logarithm in base 10 of that
number and multiply by 20. Written symbolically, this looks like
= 20 log
Also included with the idea of amplification and important in everyday life is the
concept of frequency response. Although there is no filter in this circuit, the output
voltages may be different at different frequencies. This is because the amplifier can act as
a natural filter, and amplify different frequency signals at slightly different rates.
This lab marks the first time this class has dealt with integrated circuit (IC) chips.