Amplified Ear Circuit

This is a project circuit is use for 32 Ohms impedance mini-earphones, can detect very remote sounds. This circuit is work with based on transistor. This is the figure of the circuit.


The heart of the circuit is a constant-volume control. 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.

Part:
P1_____________22K Log. Potentiometer (see Notes)
R1,R9__________10K 1/4W Resistors
R2______________1M 1/4W Resistor
R3______________4K7 1/4W Resistor
R4,R7_________100K 1/4W Resistor
R5______________3K9 1/4W Resistor
R6______________1K5 1/4W Resistor
R8_____________100R 1/4W Resistor
C1,C2_________100nF 63V Polyester or Ceramic Capacitors
C3,C6___________1΅F 63V Polyester or Ceramic Capacitors
C4_____________10΅F 25V Electrolytic Capacitor
C5____________470΅F 25V Electrolytic Capacitor
D1___________1N4148 75V 150mA Diode
Q1,Q2,Q3,_____BC547 45V 100mA NPN Transistors
Q4____________BC337 45V 800mA NPN Transistor
MIC1__________Miniature electret microphone
SW1____________SPST Switch (Ganged with P1)
J1_____________Stereo 3mm. Jack socket
B1_____________1.5V Battery (AA or AAA cell etc.)