Audio Processing Circuitry for Power Speaker

Design overview

The aux port emits analog signals when playing music, and circuitry needs to be built to take this weak signal and use it to drive a large speaker. My goal with this project was to make the speaker on the left perform at high volumes without noticeable noise.

The circuit:

• First stage combines left and right channel voltage signals
• Op-amp stage amplifies the voltage from mV range to the V range
• Low-pass RC filter filters out noise added in the amplification process
• Push-pull stage pushes more current into the speakers to drive the large discs

Designing the low-pass RC filter

The op-amp stage I used to amplify the signal had issues of adding a lot of high frequency noise to the circuit. While a variety of solutions exist, for my first analog circuit I went with a simple RC low-pass filter. Analyzing the signal after amplification in the frequency domain showed the noisy frequencies. Taking into account the frequency range I wanted to filter out along with a 10 kΩ resistor, I could solve for what capacitor I needed.