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.

Assembled pink noise generator kit.

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.

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.

Pink noise generator test setup with LM386 amplifier.

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.

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

Calculator for audio output transformers

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M...

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