This repository contains the design files, simulation data, and documentation for a three-band audio pre-amplifier circuit. This project was completed as part of the EN2111 - Electronic Circuit Design course at the University of Moratuwa.
This project is a comprehensive analog circuit design for a three-band audio pre-amplifier. It features a split output for subwoofer systems and incorporates filters, feedback, and amplification stages. The pre-amplifier serves as a front-end signal conditioner, enhancing audio quality before the signal is sent to a power amplifier. The system amplifies low-level signals from sources like mobile phones or PCs and provides equalization controls.
- Three-Band Equalizer: Independent control over bass, mid, and treble frequencies.
- Subwoofer Output: A dedicated output for low-frequency signals to drive a subwoofer.
- Active Filters: Utilizes active filters for precise frequency control.
- Impedance Matching: An input buffer stage prevents loading effects and ensures proper impedance matching with the audio source.
- Detailed Tone Control: Potentiometers allow users to boost or cut the bass, mid, and treble bands.
The pre-amplifier circuit is divided into several key stages:
- Input Buffer: A unity-gain buffer using a TL072 op-amp is placed at the input.
- Filter Bank (Equalizer Section): The incoming signal is split into three bands using active filters.
- Low-Pass Filter (Bass/Subwoofer):
- Topology: Multiple Feedback (MFB)
- Cutoff Frequency: Approximately 211 Hz
- Gain: Configured for ~13 dB
- Mid-Band Filter:
- Topology: Cascaded High-Pass and Low-Pass Sallen-Key filters.
- HPF Cutoff: Approximately 420 Hz
- LPF Cutoff: Approximately 2.3 kHz
- Gain: Approximately 1.586
- High-Pass Filter (Treble):
- Topology: Sallen-Key
- Cutoff Frequency: Approximately 3.3 kHz - 4 kHz
- Low-Pass Filter (Bass/Subwoofer):
The design was validated through both simulation and real-world measurements. The results from both were closely aligned, confirming the effectiveness of the design and implementation.
- Bass (Low-Pass Filter): The simulated cutoff frequency of ~211 Hz matched the real-world response, with a clear 40 dB/decade roll-off.
- Mid (Band-Pass Filter): The cascaded filters produced a clean mid-band centered between approximately 800 Hz and 1.6 kHz with a gain of +3.6 dB.
- Treble (High-Pass Filter): The treble stage demonstrated consistent behavior between simulation and real measurements, with the gain rising around 3.5-4 kHz and flattening at +2.7 dB beyond 10 kHz.
Minor differences observed are attributed to component tolerances, breadboard layout effects, and op-amp limitations at higher frequencies.