Electronic Circuit

Amplifier parts:

P1_____________22K  Log. Potentiometer (Dual-gang for stereo)

R1______________1K  1/4W Resistor
R2______________4K7 1/4W Resistor
R3____________100R  1/4W Resistor
R4______________4K7 1/4W Resistor
R5_____________82K  1/4W Resistor
R6_____________10R  1/2W Resistor
R7_______________R22  4W Resistor (wirewound)
R8______________1K  1/2W Trimmer Cermet (optional)

C1____________470nF  63V Polyester Capacitor
C2,C5_________100µF   3V Tantalum bead Capacitors
C3,C4_________470µF  25V Electrolytic Capacitors
C6____________100nF  63V Polyester Capacitor

D1___________1N4148  75V 150mA Diode

IC1________TLE2141C  Low noise, high voltage, high slew-rate Op-amp

Q1____________BC182  50V 100mA NPN Transistor
Q2____________BC212  50V 100mA PNP Transistor
Q3___________TIP42A  60V 6A    PNP Transistor
Q4___________TIP41A  60V 6A    NPN Transistor

J1______________RCA  audio input socket

Power supply parts:

R9______________2K2 1/4W Resistor

C7,C8________4700µF 25V Electrolytic Capacitors

D2_____________100V 4A Diode bridge
D3_____________5mm. Red LED

T1_____________220V Primary, 15 + 15V Secondary, 50VA Mains transformer

PL1____________Male Mains plug

SW1____________SPST Mains switch

Notes:

* Can be directly connected to CD players, tuners and tape recorders.
* Do not exceed 23 + 23V supply.
* Q3 and Q4 must be mounted on heatsink.
* D1 must be in thermal contact with Q1.
* Quiescent current (best measured with an Avo-meter in series with Q3 Emitter) is not critical.
* Adjust R3 to read a current between 20 to 30 mA with no input signal.
* To facilitate quiescent current setting add R8 (optional).
* A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of J1, P1, C2, C3 & C4. Connect C6 to the output ground.
* Then connect separately the input and output grounds to the power supply ground.

Technical data:

Output power:
18 Watt RMS into 8 Ohm (1KHz sine wave)
Sensitivity:
150mV input for 18W output
Frequency response:
30Hz to 20KHz -1dB
Total harmonic distortion @ 1KHz:
0.1W 0.02% 1W 0.01% 5W 0.01% 10W 0.03%
Total harmonic distortion @10KHz:
0.1W 0.04% 1W 0.05% 5W 0.06% 10W 0.15%
Unconditionally stable on capacitive loads

Q1 amplifies the input signal via C4 from the electret microphone.
Q2 acts as an oscillator and the signal coming off C2 is fed onto the base of Q2.
L1/C1 is a so called ‘tank’ circuit and operates in the 88-105MHz band on your regular AM/FM radio dial.
L1 is a 1uH variable inductor coil to be able to tune it a little bit, and the range of 1uH is approximate.
The antenna can be as simple as a 8″ (21cm) piece of wire of any kind.

List:
R1 = 10K (brown-black-orange)
R2,R3 = 100K (brown-black-yellow)
R4 = 470 ohm (yellow-violet-brown)
C1,C3 = 4.7pF (4p7), ceramic
C2,C4 = 4.7uF-16V, electrolytic
C5 = 0.001uF (1nF), ceramic
C6 = 470pF, ceramic
Q1,Q2 = 2N2222, NPN transistor
L1 = 1uH, variable inductor
Mic = Electret mike, 2 wires