Project Overview
Final Breadboard Implementation
We built an analog pink-noise generator using a simple three-stage approach: a white-noise source, passive 1/f spectral shaping, and clean amplification. The goal was a -3 dB/octave pink-noise spectrum centered at 0 V with a user-adjustable output up to 2 V peak. The design was developed in simulation and validated with measurements.
Noise Source
Physical white-noise generation using a reverse-biased transistor
1/f Shaping
Passive RC network targets a -3 dB/octave spectrum
Output Level
Simple gain control for up to 2 V peak
Validated
Designed in simulation and confirmed with real measurements
Core Specifications
- Output Noise: Pink Noise (approx. -3 dB/octave PSD slope)
- Output Amplitude: Adjustable up to 2V peak (via potentiometer)
- DC Offset: Centered at 0V
- Power Supply: Dual ±9V DC (from two 9V batteries in series)
- Key Components: BC337-16 BJT, TL072CP Op-Amps, Passive RC Network
Circuit Design
Three-Stage Architecture
White Noise Generation
Generates white noise using the inherent avalanche breakdown noise of a reverse-biased BJT (BC337-16)
Spectral Shaping
Shapes the spectrum using a passive RC shelving filter network to achieve the -3 dB/octave slope
Amplification
Amplifies and buffers the signal with adjustable gain control for practical output levels
Circuit Schematic
Final circuit schematic showing all three stages
Design Highlights
- White-Noise Source: Reverse-biased transistor used for physical noise generation
- Spectral Shaping: Cascaded passive RC stages approximate a -3 dB/octave slope
- Amplification: High-gain stage lifts the shaped signal to usable levels
- Level Control: User-adjustable output centered at 0 V
Results & Performance
Key Findings
Challenge
The BC337-16 BJTs exhibited lower-than-expected avalanche breakdown noise amplitude
Solution
Increased first-stage gain by replacing the 100kΩ feedback resistor with 10MΩ (100× gain increase)
Trade-off
While achieving required output voltage, resulted in a spectrum slightly "whiter" than ideal pink noise
Performance Metrics
- Spectral Slope: Achieved approximately -3 dB/octave across most of the audio band
- Output Amplitude: Successfully met the 2V peak specification with adjustable control
- Project Score: 145.16 (normalized error metric for adherence to ideal pink noise)
- Ideal Reference: Ideal pink noise scored ~36 on the same metric
Simulation vs. Real Results Comparison
Simulation
Simulated PSD with Model
Real Circuit
Measured PSD with Model
Simulation
Simulated PSD Linear Fit
Real Circuit
Measured PSD Linear Fit
Simulation
Simulated Voltage vs. Time
Real Circuit
Measured Voltage vs. Time
Simulation
Simulated Distribution
Real Circuit
Measured Distribution
Audio Samples
Explore and listen to recorded signals from the project:
Build Progress
Early Prototype on Breadboard
Final Breadboard Implementation
Future Improvements
While this project successfully demonstrates the core concepts of analog pink noise generation, several enhancements could significantly improve performance:
Enhanced Noise Source
- Evaluate Zener diodes as alternative noise sources
- Screen/select BJTs with higher avalanche noise output
- Consider specialized noise diode ICs for consistent performance
Optimized Filter Design
- Implement additional shelving stages for closer approximation to ideal -3 dB/octave slope
- Explore active filter topologies for better spectral shaping
Power Supply Enhancement
- Replace batteries with a regulated ±9V or ±12V supply for consistent long-term operation
- Add voltage regulation and additional filtering to minimize power supply noise