This audio amplifier 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 1,5V Earphones Audio AmplifierThe 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.
Typical current drawing: 7,5mA.
A noteworthy feature of this circuit is 1,5V battery operation.
Typical current drawing: 7,5mA.
List Component
- P1: 22K Log. Potentiometer
- 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: 1µF 63V Polyester or Ceramic Capacitors
- C4: 10µF 25V Electrolytic Capacitor
- C5: 470µF 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
- J1: Stereo 3mm. Jack socket
- B1: 1.5V Battery
Source
