Many electronic circuits having audio amplifiers are available today. This 40W amplifier using TDA 1514 is one among these circuits with TDA 1514 (high performance hi-fi amplifier from Philips) as central part. The audio amplifier IC has some added features like thermal protection, low harmonic distortion, mute standby facility etc. This IC should provided with a proper heat sink in Printed Circuit Board (PCB).
The input signal is given to pin1 of the IC 1514 as shown in the circuit diagram. The capacitor connected to this pin accomplishes decoupling. Closed loop gain of the amplifier is determined by the resistors R3 (20k) and R4 (680 ohm). This gain ranges from 20 dB to 64 dB. Boot strapping is provided by capacitor C5 and resistors R7 (80 ohm) and R6 (150 ohm). In some cases boot-strapping is not required. At that time pin6 and pin7 can be short circuited. One of the main disadvantages of doing this is the reduction of amplifier gain by 10% of the gain with the boot-strapping elements connected. Resistor R1 acts as input bias resistor and it has some effect on input impedance of the amplifier. For improving frequency response of the amplifier and correcting loud speaker impedance, a special network called Zobel network is used in this circuit. Here Zobel network is formed by resistor R2 (3.3 ohm) and capacitor C4.
The power supply required for this amplifier is +25 /-25 V DC dual supplies. It is better to use +25/-25 V DC, 4A dual power supply for this circuit. This amplifier can deliver a maximum output power of 40 W to an 8 ohm speaker hence the name 40W amplifier. In order to get desired output, assemble this circuit on a good quality PCB.