Desiging An Audio Amplifier

Description

More specifically, designing the circuit in such a way that the slew rate and cutoff frequency limitations of the op-amp do not affect the signal. Later on taking into account the DC offset when working with microphones.

The specifications of the circuit are:
Vi = 10mv (pk-pk)
Vo = 5V (pk-pk)
Desired Bandwidth = 100Hz - 20kHz
Aclo = 500 V/V

The audio amplifier will either be made from an LM741 or LM318, eventually I chose to use 2 LM741's for there cheaper price.

Initially, tests and simulations as well as lab work was done for the LM741 circuit. As seen in the oscilloscope screenshots the circuit works well to amplify the signal within the desired bandwidth (100Hz - 20kHz).

The next step of this project would be to use an actual microphone and amplify its sound so that it is audible in a small speaker.

Microphone planning to use => Electret microphone, Model #: 07-9
Speaker planning to use => McBridge AZ-30s

Project Logs

Collapse logs

Building the Circuit and Testing the Properties
Alvi Ahmed • 02/21/2019 at 21:18 • 0 comments

Circuit being built:

Oscilloscope Screen Shots:
NOTE: The yellow traces are the input waveforms, whereas the green traces are the output waveforms.
Waveform results @ 100Hz:

Waveform results @ 20kHz:
It seems that LM741 amplifier circuit is working according to specifications.
Therefore the next step after this will be to apply the microphone and speaker circuitry and observe if it correctly amplifies the voice.
However it should be noted that further calculations will have to be made to avoid distortion and noise. I am mainly talking about the potential for DC offset and bias currents, which will have to be nulled out.
Simulation in NI Multisim
Alvi Ahmed • 02/21/2019 at 21:06 • 0 comments

Circuit :

Input Voltage (10mV (pk-pk) @ 20kHz):

Output Voltage (5V (pk-pk) @ 20 kHz):

In conclusion the schematic seems to be working well in simulation, therefore it is time to build it and see if the results hold in the real world.
Calculations of Audio Amplifier with both LM741 and LM318
Alvi Ahmed • 02/21/2019 at 20:52 • 0 comments

For LM741

Pg 1:

Pg2:

For LM318

Pg1:

For this project I will be going with the LM741 version of the amplifier circuit. Even though the LM318 version of the circuit is cheaper, at this time I only have LM741 op-amps at my disposal.