Power amplifier electronic circuits-tube audio rf amplifiers

Circuit Description

The circuit of 2×32 Watts stereo amplifier consists of two channels. In both the channels the central component is the IC TDA 2050 V developed by ST Microelectronics. The audio input signal is given to each of the channels in non-inverting input pin of IC TDA 2050V. For decoupling purpose, capacitor 1 uF (C1 and C8) is connected so that input can be given through it as shown in the circuit diagram.

The gain of the amplifier in each channel is determined by the resistors 22k (R1 and R5) and 680 ohm (R2 and R6). The value of gain is the ratio of 22K and 680 ohm. To improve the frequency response of the amplifier, a network called Zobel network is used in this circuit. Here the Zobel network is the combination of 2.2 ohm (R4 and R8) resistor and 0.47 uF (C3 and C14) capacitor that are connected in series between the amplifier output and ground in both the channels. By the effect of Zobel network, impedance of the speaker appears as resistive load and that improves frequency response of the amplifier.

The central part of the circuit TDA 2050V IC is an integrated monolithic 32 watt class B audio amplifier. It has some extra features like short circuit protection, low distortion, thermal protection etc. and it is available in Pentawatt package. Proper heat sink should be provided for this IC in PCB. Power supply required for this circuit is 18 V DC dual supplies. In order to get maximum output power, the input required is 200m Vpp RMS. Volume control is done by 10K pots connected at input lines. Assembling this circuit on a good quality PCB will give the desired output.

Circuit Diagram

Simple stereo amplifier circuit

Circuit Description

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.

Circuit Diagram

40 watts amplifier

About The Circuit

Clipping is one of the main problems that causes distortion in amplifiers. It causes the amplitude level of a waveform to drop suddenly before it reaches the limit that it was supposed to reach. Well, here is a simple circuit that will help to detect the clipping in a waveform. The clipping can be identified as an LED is kept as the alert indicator when a clipping occours.

This circuit will show correct accuracy if you are able to make it on a high quality PCB. The circuit is mainly based on the working of two operational amplifers (TL 082) inside IC1. They act as window comparators. All it does is to detect the input signal and find out its positive or negative peak value. Correct calibration of the circuit can be done with the POT R5, while POT R1 has to be adjusted to the level at which the LED is supposed to glow.

As we can see Diodes D1 and D2 are connected to the output of the operational amplifier. They are used to drive the transistor Q1 which further drives the LED to glow. A very small time delay is induced by the capacitor C5 so as to identify rapid as well as short peaks. The circuit will easily work with the help of a 9 Volt battery. The circuit is very useful and can be used on all types of power amplifiers, pre-amplifiers and mixers.

Circuit Schematic