Useful to pay attention in faint sounds, 1.5V Battery operation
This circuit, related to 32 Ohm impedance mini-earphones, can discover very faraway sounds. Useful for theatre, cinema and lecture goers: every phrase will most probably be clearly heard. You may additionally hearken to your television set at an awfully low quantity, fending off to hassle household and neighbors. Even when you've got a flawless hearing, you may just additionally discover sudden sounds the usage of this device: a remote chicken twittering will seem very close to you.
Circuit Diagram:
Parts :
P1 = 22K
R1 = 10K
R2 = 1M
R3 = 4K7
R4 = 100K
R5 = 3K9
R6 = 1K5
R7 = 100K
R8 = 100R
R9 = 10K
C1 = 100nF 63V
C2 = 100nF 63V
C3 = 1µF 63V
C4 = 10µF 25V
C5 = 470µF 25V
C6 = 1µF 63V
D1 = 1N4148
Q1 = BC547
Q2 = BC547
Q3 = BC547
Q4 = BC337
J1 = Stereo 3mm. Jack socket
B1 = 1.5V Battery (AA or AAA cell etc.)
SW1 = SPST Switch (Ganged with P1)
MIC1 = Miniature electret microphone
R1 = 10K
R2 = 1M
R3 = 4K7
R4 = 100K
R5 = 3K9
R6 = 1K5
R7 = 100K
R8 = 100R
R9 = 10K
C1 = 100nF 63V
C2 = 100nF 63V
C3 = 1µF 63V
C4 = 10µF 25V
C5 = 470µF 25V
C6 = 1µF 63V
D1 = 1N4148
Q1 = BC547
Q2 = BC547
Q3 = BC547
Q4 = BC337
J1 = Stereo 3mm. Jack socket
B1 = 1.5V Battery (AA or AAA cell etc.)
SW1 = SPST Switch (Ganged with P1)
MIC1 = Miniature electret microphone
Circuit Operation :
The heart of the circuit is a continuing-volume keep watch over amplifier. All the alerts picked-up by using the microphone are amplified at a constant degree of about 1 Volt height to peak. In this fashion very low amplitude audio alerts are highly amplified and excessive amplitude ones are limited. This operation is entire by Q3, modifying the bias of Q1 (hence its AC gain) by means of R2.
A be consciousworthy function of this circuit is 1.5V battery operation. Typical present drawing: 7.5mA.
Notes:
- Due to the constant-volume control, some users may imagine P1 quantity regulate needless. In most instances it may just be neglected, connecting C6 to C3. In this case use a SPST slider or toggle swap as SW1.
- Please word the stereo output Jack socket (J1) connections: most effective the 2 inside connections are used, leaving open the exterior one. In this method the 2 earpieces are wired in series, permitting mono operation and most effective load impedance to Q4 (64 Ohm).
- Using suitable miniature components, this circuit can additionally be enclosed in an awfully small field, provided via a clip and hanged on ones garments or slipped into a pocket.
- Gary Pechon from Canada suggested that the Amplified Ear is so sensitive that he can hear a whisper 7 meters throughout the room.
- He hooked a small relay coil to the input and used to be ready to locate energy traces in hellos wall. He used to be also ready to hear the neighbors stereo perfectly: he may pick up the indicators despatched to the speaker voice coil thru a plaster wall.
- Gary suggests that this circuit might make additionally a excellent electronic stethoscope.
http://www.ecircuitslab.com/2011/06/amplified-ear-circuit.html
