Analog Audio Equalizer

Overview (Nov - Dec 2025)

Designed, prototyped, and tested an analog signal processing system capable of real-time audio frequency molding and power amplification. The system splits an input signal into bass, mid-range, and treble bands. This allows for adjustable gain changes before recombining and driving a physical speaker.

Schematic

The system isolates bass, mid, and treble via passive RC networks before independent gain adjustment through LM324 inverting amplifier stages. Processed signals are merged using an LF356 inverting summing amplifier with master volume control. The final output drives an 8Ω speaker via an LM386 power amplifier, delivering over 580mW of power

Full Schematic of Analog Audio Equalizer

Filter Design & Testing

Each band's cutoff was checked with an oscilloscope's Frequency Response Analysis function, sweeping the input and reading gain and phase directly off the trace.

Bass

Low-Pass Filter
302 Hz measured | 320 Hz target

Mid

Band-Pass Filter
341.5 Hz–2.93 kHz measured | 320–3200 Hz target

Treble

3.02 kHz measured | 3200 Hz target

Low Pass FRA

Mid Pass FRA

High Pass FRA

Results

All three bands held within the required tolerance at both minimum and maximum gain, attenuating down to near-silence and amplifying cleanly at full volume.

Key Performance Metrics

584.8 mW delivered to the 8Ω speaker (exceeds the 400 mW requirement)
10.18 mV total ripple (within the 15 mV specification)
6.3% largest error at maximum volume (within the ±10% tolerance)

Waveform & Oscilloscope Measurements

Minimum Gain (100 Hz): 14.4 mV RMS
Maximum Gain (100 Hz): 95.04 mV RMS
Ripple Sweep Across Passband: 10.18 mV total ripple
Power Amplifier Output (8Ω Load): 2.16 V RMS

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