Audio Noise Generator Schematic

Description: This simple circuit generates both white and pink noise. Transistor Q1 is utilized as a zener diode. The base-emitter junction is reverse-biased and enters zener breakdown at approximately 7 to 8 volts. The zener noise current from Q1 flows into the base of Q2, producing an output of about 150 millivolts of white noise. To convert the white noise to pink noise, a filter is necessary, which provides a 3 dB cut per octave as the frequency increases. Since this filter significantly attenuates the noise, an amplifier is incorporated to restore the output level. Transistor Q3 serves as this amplifier, and the pink noise filter is configured as a feedback network between the collector and base to achieve the desired gain-versus-frequency characteristics of the transistor. The output from transistor Q3 delivers the required pink noise to the designated output socket.

This circuit effectively demonstrates the generation of both white and pink noise through a straightforward design utilizing transistors and a filter. The key components include three transistors: Q1, which acts as a zener diode to create white noise; Q2, which amplifies the white noise signal; and Q3, which serves as the final amplifier to produce pink noise.

Transistor Q1 operates in reverse bias, entering zener breakdown to generate noise at its collector. The noise current produced is then directed to the base of Q2, where it is amplified. The output from Q2 is a low-level white noise signal, which is approximately 150 millivolts.

To convert this white noise into pink noise, a filter is required that attenuates the higher frequencies at a rate of 3 dB per octave. This filter is crucial for achieving the characteristic frequency response of pink noise, which has equal energy per octave. The filter is implemented in the feedback path of Q3, allowing for precise control over the gain and frequency response of the overall circuit.

Transistor Q3 amplifies the filtered white noise, compensating for the attenuation introduced by the filter. The feedback network between the collector and base of Q3 is designed to optimize the gain characteristics, ensuring that the output maintains the desired pink noise profile. The resulting pink noise is then sent to the output socket, ready for use in various applications such as audio testing, sound masking, or electronic music production.

Overall, this circuit illustrates a practical approach to generating colored noise through the use of basic electronic components, showcasing the interplay between noise generation, filtering, and amplification in audio applications.This simple circuit generates both white and pin noise. Transistor Q1 is used as a zener diode. The normal base-emitter junction is reverse-biased and goes into zener breakdown at about 7 to 8 volts. The zener noise current from Q G flows into the base of Q2 such that an output of about 150 millivolts of white noise is available.

To convert the wh ite noise to pink, a filter is required which provides a 3 dB cut per octave as the frequency increases Since such a filter attenuates the noise considerably an amplifier is used to restore the output level. Transistor Q3 is this amplifier and the pink noise filter is connected as a feedback network, between collector and base in order to obtain the required characteristic by controlling the gain-versus-frequency of the transistor.

The output of transistor Q3 is thus the pink noise required and is fed to the relevant output socket.