Stereo Amplifier Project at Berthoud High School
Scott Kindt and Matt Duwe
In September of 2011, my physics classes were given the task of ordering the parts, and building a functioning stereo system. The physics students would need to collaborate with students in Principles of Engineering for the design and production of their stereo box. The students in Algebra II would also be involved with performing a number of audio tests on the stereos. The finished product would be able to take the audio signal from an I-Pod, amplify this signal and play the music through a pair of speakers.
Between the two physics classes there were seven different groups. Each group has a leader called the junior fellow. The groups are then divided into project teams where students work on the speakers, power supply, or amplifier circuit. When ordering parts, the students had a budget of $250 and they had to determine how to divide their budget between the speaker parts, power supply parts and amplifier circuit. When the project is finished, students will have the option to purchase their stereo. The stereos which are not purchased will be auctioned off at the Berthoud Bash fund raiser in the spring.
Speaker Design Team: The only design constraint is that the speaker uses a two way, woofer and tweeter design. Based on the frequency response of the components, students used a computer simulation to determine the values for their capacitors and inductors in the crossover. They were also required to build their own speaker box and calculate the port tube length if they chose use one in their speaker box.
Amplifier Design Team: The amplifier team could choose between the LM3886 and LM3875 amplifier chip. They had to design and etch two amplifier circuit boards for the left and right channels. These circuit boards were then connected to the power supply circuit board.
Power Supply Team: This team had to use their transformer to step down the 110 AC volts from a wall outlet and convert this to DC. This was accomplished by designing and etching an AC to DC rectifier circuit board. The final output voltage had to be in the operating range of the amplifier chip that their group was using.
Testing: Both the physics students and the Algebra II classes were involved in testing the stereo systems. The following tests were performed and this data was used to make the science poster.
Speaker frequency Response from 20 Hz to 20 kHz, Speaker crossover frequency, maximum peak power consumption in watts, thermal test of amplifier (time vs operating temp), 3db gain bandwidth test, DC voltage output from power supply rectifier circuit.
More detailed information on this project can be found on Scott Kindt's web page: