Remote Listening Amplifier (ART432E)

For direct remote listening we can use a small amplifier that powers a headset. A battery-powered amplifier that can be loaded into a case along with the microphone is an interesting device for the detective.

This article is part of one of my e-books.

In figure 1 we have an amplifier circuit that can be used for this purpose.


Figure 1 - Amplifier circuit
Figure 1 - Amplifier circuit


This circuit is of excellent sensitivity and can power both a handset and a small speaker. Note that speakers are not suitable for this type of application, because being close to the microphone, which is high gain, can cause acoustic feedback, that is, a strong whistle that prevents the hearing of anything.

Figure 2 shows what happens.


Figure 2 - Microphone
Figure 2 - Microphone


The phone itself must be of the padded type so that it does not "escape" any sound and it will provoke the microphone whistle or acoustic feedback.

A printed circuit board for the amplifier is shown in figure 3.


Figure 3 - Board for the amplifier
Figure 3 - Board for the amplifier




CI-1 -TDA7052 - integrated circuit

Q1 - BC547 - general purpose NPN transistor



R1 - 330 k - resistor (orange, orange, yellow)

R2 - 10 k - resistor (brown, black, orange)

P1 - 10 k - potentiometer



C1 - 10 uF x 6 V - electrolytic capacitor

C2 - 22 uF x 6V - electrolytic capacitor

C3 - 100 uF x 6 V - electrolytic capacitor



S1 - 6 V - 4 small batteries

S1 - Single switch

X1- 8 to 100 ohms handset

MIC - Electret Microphone

Printed circuit board, mounting box, integrated socket, telephone jack, battery holder, wires, solder.