AUDIO FREQUENCY LIGHT MODULATOR SCHEMATIC DIAGRAM

AUDIO FREQUENCY LIGHT MODULATOR SCHEMATIC DIAGRAM
The distance between receiver and transmitter circuit depends on the environment. Light has function to replace cable from audio source to speaker. Transformer X2 is utilized to lock the audio signal. VR1 works as the amplitudo modulator from the T1 signal output.

Parts list :

Resistor R1: 47k ohm
Resistor R2 : 22k ohm
Resistor R3 : 220 ohm
Diode D1-D7 : 1N4001
VR1 : 1k ohm
Polar capacitor C1 : 470 uF/25V
Polar capacitor C2 : 1 uF
Capacitor C3 : 0.1 uF
Transistor T1-T2 : BC148
Transformer X1 : 220 V AC/0-12V AC
X2 : AF output
Transistor SCR1-SCR2 : BA654

MINI AUDIO AMPLIFIER SCHEMATIC DIAGRAM

MINI AUDIO AMPLIFIER SCHEMATIC DIAGRAM
“mini” audio amplifier referring to its small dimension and small output. It is intended for earpiece/earphone use. The characteristics are consume power less than 3mA, using push-pull output which can drive the earpiece to very loud level when audio is detected, whole circuit DC coupled, therefore makes it difficult to set up. Due to its size, be careful when assemble the circuit.

The 8k2 across the 47u sets the emitter voltage on the BC 547 and this turns it on. The collector is directly connected to the base of a BC 557, called the driver transistor. Both these transistors are now turned on and the output of the BC 557 causes current to flow through the 1k and 470R resistors so that the voltage developed across each resistor turns on the two output transistors. The end result is mid-rail voltage on the join of the two emitters. The two most critical components are 8k2 between the emitter of the first transistor and 0v rail and the 470R resistor.