AudioGainX — Common-Emitter Preamplifier

Overview

A common-emitter BJT preamplifier designed for public-address systems, engineered to hold a stable, low-noise gain figure across the entire 20 Hz–20 kHz audio band — and explicitly validated against real oscilloscope measurement rather than simulation alone.

Architecture

Single-stage common-emitter BJT amplifier with a carefully selected biasing network and coupling/bypass capacitors sized for the target frequency response.

Key Features

• Biasing network engineered for a stable quiescent operating point.
• Coupling and bypass capacitor sizing tuned for full audio-band frequency response.
• Target voltage gain (dB) calculated analytically before simulation.
• Frequency response validated in both Multisim/Proteus simulation and physical oscilloscope measurement.

Development Process

• Calculated target gain and biasing point analytically before touching a simulator.
• Simulated the design in Multisim/Proteus to verify frequency response predictions.
• Built and measured the physical circuit on an oscilloscope to compare theoretical vs. practical results.
• Reconciled discrepancies between theory and measurement to finalize component values.

Challenges & Solutions

Results & Impact

The final circuit achieved the target voltage gain with a validated, stable frequency response across the full audio band, confirmed by direct oscilloscope measurement.

Future Improvements

• Add active noise filtering for line-level interference.
• Explore a two-stage design for higher gain headroom.
• Migrate to a PCB layout from breadboard prototype.