Here the simple, low cost and easy audio booster circuit. It uses a transistor of 2N3392 ad the main amplifier.
Component List:
| R1 = 47K R2 = 470K R3 = 10K R4 = 560R R5 = 270R C1 = 0.1uF/25v C2 = 3.3uF/25v C3 = 470uF/25V |
P1 = 100K Q1 = 2N3392 D1 = 5mm. Red Led B1 = 9v Battery J1 = RCA Audio Input Socket J2 = RCA Audio Output Socket S1 = On-Off Switch |
This small audio booster circuit has a maximum gain of around 22 dB (voltage gain). The frequency response of the amplifier is decided primarily by the value of just a few components, primarily C1 and R1. The values within the schematic design present a response of ±3.0 dB from about 120 Hz to higher than 20,000 Hz. In fact, the frequency response is ruler flat from about 170 Hz to more than 20,000 Hz; it is the low end that deviates from a flat frequency response.
The low end’s roll-off is mainly a function of capacitor C1 (considering that RI’s resistive amount is fixed). If C1’s value is changed to 0.1 pF, the low end’s comer frequency-the frequency at which the low-end roll-off starts-is decreased to about 70 Hz. Should you need an even deeper low-end roll-off, modify C1 to a 1.0 pF capacitor; if it is an electrolytic type, make certain that it is installed into the circuit together with the appropriate polarity, with the positive terminal linked to Q1’s base terminal.
Take note that you must connect this small audio booster circuit before the power amplifier circuit.