Power amplifier electronic circuits-tube audio rf amplifiers

Circuit Description

The circuit diagram of Pocket headphone amplifier has been given here. The core part of this circuit is the operational amplifier IC OPA 134 developed by BURR-BROWN Semiconductors. In addition to this the circuit contains some passive components also.

The IC OPA 134 is used in this circuit as a non-inverting amplifier. High input impedance for this IC is provided by the FET biased input stage and this also makes this IC suitable for audio applications. A switch S1 is used in this circuit to accomplish circuit ON/OFF. An indicator LED shows whether the circuit is powered or not. Resistor R2 (100K) and capacitor C1 (0.1 uF) connected to the non-inverting terminal (pin 3) of OPA 134 is a high-pass filter network having a corner frequency approximately 15 KHz. To reduce noise and distortion in output, a load resistance R5 (20 ohm) is used. This load resistance also stabilizes the virtual ground. The output of this circuit is DC coupled. The variable resistor port R1 (47K) is the volume controller of this amplifier circuit.

Split power supply of +/- 4.5 V is required for IC OPA 134. This obtained from a 9V PP3 battery using a network composed of resistors R6 (10K), R7 (4.7K), R8 (4.7K) and capacitors C2 (220 uF), C3 (220 uF).

Circuit Diagram

Simple Pocket Headphone Amplifier Circuit

Notes

• Use a good quality PCB to assemble components.
• Sound sources like MP3 players, I Pods, mobile phones etc can be plugged in this circuit.
• IC OPA 134 is specially designed for audio applications.

Circuit Description

Automatic cooler fan for amplifiers is a circuit introduced for the purpose of saving power in amplifier circuits. This circuit switches ON and switches OFF the cooler fan of heat sink according to its temperature. The cooler fan will turn ON when heat sink temperature exceeds a certain value and will turn OFF temperature become lower than a certain value. Automatic cooler circuit does it always so that effective working of cooling fan occurs and that saves power.

In this circuit thermistors are used as temperature sensors. Here negative temperature coefficient thermistor (NTC) is used. NTC means as temperature increases the resistance of NTC thermistor decreases. Resistor R2 in circuit diagram is an NTC thermistor. Here LM311 IC is used as a comparator which is having an inverting (pin 3) and non-inverting (pin 2) input pins. The junction of R1 and R2 is connected to pin 3. At pin 2 a reference voltage is given using resistor R3. The comparator compares voltage at its inverting and non-inverting terminals. When voltage at inverting terminal becomes less than that at non inverting terminal, the output of comparator becomes high. This will turn ON transistor Q1 which triggers relay and cooler fan will turn ON. Fan will be turned off when voltage at inverting terminal becomes higher than non-inverting terminal.

12 V DC supply is used as power supply in this circuit. The relay K1 can be a 12V, 200 ohm, SPST relay. Calibration of this circuit can be done by adjusting R3.

Circuit Diagram

Automatic Cooler Fan Circuit for Amplifiers

Notes

• Use Vero board to assemble components.
• Diode D1 is a freewheeling diode.
• LED D2 acts as an indicator, it will glow when fan is ON.

Circuit Description

4×15 watt power amplifier consists of four channels of amplifiers. The core part of the circuit is 15W BTL X 2 channel audio power amplifier IC TA 8215 developed by Toshiba. In this power amplifier circuit, two TA 8215 ICs are used. This is for obtaining four channels that is two channels from each IC. TA 8215 is an IC with power amplifier stages and preamplifier integrated inside it. Pins 7 and 19 are Vcc and pins 13 and 14 are ground of power amplifier stage. Vcc and ground pins should be connected to positive supply and ground respectively. Pin 9 is the Vcc of internal pre-amplifier and Pin 5 is its ground. Vcc is connected to positive supply and ground pin to ground through a 10 ohm resistor which separates input ground from common ground and this improves noise rejection.

In this circuit power supply decoupling is accomplished by 100 uF (C6 and C20) capacitor. High frequency stability in this circuit is achieved by the resistor network connected to the output line of each of the amplifier. Volume controller in each channel is the variable resistors of 10k (R3, R4, R12 and R13). The power supply required for this amplifier is single 12 V DC supply. The maximum output power delivered from each channel of this amplifier is 15 W to a 4 ohm speaker and hence the name 4×15 W power amplifier.

Circuit Diagram

4x15 Watt Power Amplifier Circuit

Notes

• For obtaining optimum sound quality assemble above circuit on a good quality PCB
• The applications of this circuit have a wide range such as car audio systems, home theater systems, personal audio systems, public address systems etc.