This circuit, connected to 32 Ohm impedance mini-earphones, can detect very remote sounds. Useful for theatre, cinema and lecture goers: every word will be clearly heard. You can also listen to your television set at a very low volume, avoiding to bother relatives and neighbors. Even if you have a faultless hearing, you may discover unexpected sounds using this device: a remote bird twittering will seem very close to you.
Skema Rangkaian Alat Bantu PendengaranThe heart of the circuit is a constant-volume control amplifier. All the signals picked-up by the microphone are amplified at a constant level of about 1 Volt peak to peak. In this manner very low amplitude audio signals are highly amplified and high amplitude ones are limited. This operation is accomplished by Q3, modifying the bias of Q1 (hence its AC gain) by means of R2.
A noteworthy feature of this circuit is 1.5V battery operation.
List Component
P1 : 22K Log. Potentiometer R1,R9 : 10K R2 : 1M R3 : 4K7 R4,R7 : 100K R5 : 3K9 R6 : 1K5 R8 : 100R C1,C2 : 100nF C3,C6 : 1µF/63V C4 : 10µF/25V C5 : 470µF/25V D1 : 1N4148 Q1,Q2,Q3 : BC547 Q4 : BC337 MIC1 : electret microphone SW1 : SPST Switch J1 : Stereo 3mm. Jack socket B1 : 1.5V Battery (AA or AAA cell etc.)Circuit from: www.sound.westhost.com
Posted by , Published at 1:17 PM and have
