Two-Stage Audio Amplifier
Analogue two-stage amplifier with TL071 active band-pass filter and OPA551 buffer, simulated in Proteus and manufactured as a custom PCB
Overview
Designed and built a two-stage audio amplifier as a first-year university project. Stage 1 uses a TL071 op-amp configured as an inverting active band-pass filter, achieving a gain of 10.67 dB across a passband of 6.63 Hz to 28.54 kHz. Stage 2 uses an OPA551 as a unity-gain voltage follower, providing the high output current (up to 200 mA) needed to drive an 8 Ω speaker at 281 mW from a single 9 V supply. The design includes Vcc/2 virtual ground biasing, reverse polarity protection (1N4007 diodes), an LED power indicator, an on/off switch and a 2200 µF output coupling capacitor. The full circuit was simulated in Proteus, then prototyped on breadboard (dual-supply and single-supply) before being laid out as a 65 mm x 40 mm PCB with a ground plane, mitred track corners and a DRC-clean design. Measured output of 2.980 Vpp against a 3 Vpp target - a 0.67% error.
Key highlights
- ·Two-stage design: TL071 active band-pass filter (Stage 1) and OPA551 unity-gain buffer (Stage 2)
- ·Gain: 10.67 dB, passband: 6.63 Hz to 28.54 kHz, output: 2.980 Vpp into 8 Ω (281 mW)
- ·Single 9 V supply with Vcc/2 virtual ground biasing and AC coupling
- ·Reverse polarity protection, LED indicator and on/off switch
- ·65 mm x 40 mm PCB with ground plane, mitred corners and DRC-clean design
- ·Validated across Proteus simulation, dual-supply breadboard, single-supply breadboard and PCB