AVT732 B. Whisper - Whisper Hunter
The operation of the system makes an amazing impression on the user. The quietest whispers and normally inaudible noises are amplified for an unforgettable listening experience.
The circuit is perfect for various experiments related to the amplification of different sounds. This can be useful for people with mild hearing loss, and is also an ideal system for monitoring the restful sleep of young children. It will also be appreciated by people who love communication with nature.
Description of the layout
The signal from the M1 electret microphone is fed to the first stage - a non-inverting amplifier with IS1A. The gain is constant and is 23x (27 dB) - determined by resistors R5, R6. The pre-amplified signal is fed to an inverting amplifier with an IC1B cube - here the gain, or rather the attenuation, is determined by the ratio of the active resistances of the potentiometers R11 and R9 and can vary within 0 ... 1. The system is powered by one voltage, and the elements R7, R8, C5 form artificial earth circuit. Filter circuits C9, R2, C6 and R1, C4 are needed in a very high gain system and their task is to prevent self-excitation caused by signal penetration through the power circuits.
At the end of the track, the popular TDA2 IC7050 power amplifier was used. In a typical application system, it operates as a two-channel amplifier with a gain of 20 × (26 dB).
Figure 1. Schematic diagram
Installation and adjustment
The circuit diagram and the appearance of the PCB are shown in Figures 1 and 2. The components must be soldered to the PCB, preferably in the order shown in the component list. When assembling, you need to pay special attention to the method of soldering the pole elements: electrolytic capacitors, transistor, diodes. The cutout in the case of the stand and the integrated circuit must correspond to the drawing on the printed circuit board.
An electret microphone can be connected with short wires (even with cut-off resistor ends), or with a longer wire. In any case, pay attention to the polarity marked on the diagram and the board - in the microphone, the negative end is connected to the metal case.
After assembling the system, it is necessary to check very carefully whether the elements were soldered in the wrong direction or in the wrong places, whether the soldering point was closed during soldering.
After checking the correct assembly, you can connect headphones and a power source. Flawlessly assembled from working components, the amplifier will immediately work properly. First turn the potentiometer to the minimum, i.e. to the left, and then gradually increase the volume. Too much gain will cause self-awakening (on the way headphones - microphone) and a very unpleasant, loud squeak.
The system must also be powered by four AA or AAA fingers. It can also be powered by a 4,5V to 6V plug-in power supply.
