Analog Pink Noise Generator

Pink noise is an essential tool in audio testing, widely used for analyzing speaker systems, room acoustics, and crossover networks. Unlike white noise, which has equal energy across all frequencies, pink noise features equal energy per octave, making it ideal for audio response testing. This characteristic ensures that pink noise offers a flat frequency response when analyzed on a logarithmic scale, providing a more accurate representation of audio systems.

We developed a this pink noise generator to meet various audio testing requirements. This device combines simplicity and performance, featuring a minimal component count for ease of assembly without compromising accuracy and usability. This pink noise generator design uses a reverse-biased emitter-base junction of a 2SC945 transistor as the noise source. In this configuration, the transistor behaves like a noisy zener diode, producing a broad spectrum of white noise.

C101,C103 - 100μF/25V

C102,C104 - 1000μF/25V

C105,C106,C114 - 10μF/25V

C107,C115,C116 - 0.1μF/50V

C108 - 0.033μF/50V

C109 - 0.01μF/50V

C110 - 0.0033μF/50V

C111 - 0.001μF/50V

C112 - 330PF/50V

C113 - 100PF/50V

D101,D102 - 1N4007

J101 - 5.5mm DC Jack Socket

J102 - RCA Jack Socket

Q101 - TIP31

Q102 - TIP32

Q103 - 2SC945

R101,R102,R104,R105,R106 - 1KΩ (5% 1W)

R103,R107 - 2.2Ω (5% 1W)

R108,R109,R115 - 100KΩ

R110,R111,R117 - 10KΩ

R112 - 1.8MΩ

R113 - 1MΩ

R114 - 330KΩ

R116 - 33KΩ

R118 - 3.3KΩ

TP101 - Test pin (optional)

U101 - NJM4558

All resistors are 5% 1/4W unless otherwise noted

In this design the NJM4558 op-amp is used to amplify and buffer the generated noise, ensuring high input impedance, stability, and consistent performance. At this stage above generated white noise is converted into pink noise using a 3dB/octave filter, which ensures equal energy distribution per octave over the audio frequency range.

The unit operates on a single-rail DC power source, compatible with 12V to 18V inputs. At our testing we found that this kit with 2SC945 from Matsushita electric starts to generate output at 8.4V and above. As we noticed this behavior is changing from vendor to vendor. For example some 2SC945's (It's manufacturer is difficult to identify) produces output at 9.1V. By considering most of the datasheets we decided 12V as the safest voltage which guaranteed the output.

To evaluate the performance of the pink noise generator, we paired it with the Simtelic KT0001 (LM386 power amplifier) module. This setup ensured that the output noise was sufficiently amplified for practical testing scenarios. This kind of setup is useful to identifying anomalies in speakers and crossover networks, measuring and optimizing room responses for audio clarity, and for microphone calibrations. When connecting this kit to an amplifier, pre-amplifier, or other analog audio equipment, always use shielded audio cables (UL1185 or equivalent) with the shortest possible length. Long, unshielded cables may introduce hum, oscillations, and distortion in the output.

The PCB for this module was fabricated by PCBWay, who generously sponsored this project. PCBWay offers high-quality PCB manufacturing and assembling services. Also, they offer CNC and 3D printing services. The pink noise generator PCB is available to order from PCBWay. Check out the PCBWay website for its manufacturing capabilities and pricing.

This kit is also available for purchase from Simtelic as a DIY kit. It is designed with through-hole components and can be assembled and tested without the need for specialized electronic assembly tools or instruments. For more details, refer to the kit's user manual provided on the Simtelic website.