Description.
Many electronic circuits dealing with audio amplifier circuits have been published here. This is just another one and here we use the TDA 1514 high performance hi-fi amplifier from Philips. The IC has a bunch of useful features like thermal protection, mute-standby facility, low harmonic distortion etc. The amplifier operates from a dual +25/-25 V DC power supply and can deliver 40Watts output power to an 8 ohm speaker.

The audio signal to be amplified is fed to pin 1 of the IC and the capacitor C2 acts as a DC de-coupler. The resistors R3 and R4 determine the closed loop gain and it can be varied between 20 and 64 dB. Resistor R2 and capacitor C4 forms a Zobel network which corrects the loudspeaker impedance and improves the frequency response. Resistors R7, R6 and capacitor C5 are the boot-strap elements. If boot-strapping is not needed then these components can be omitted and the pin7 can be connected to pin 6, but the output power will be reduced by some 10%. R1 is the input bias resistor and it has an effect on the input impedance.

Circuit diagram.

Notes.

• Assembling the circuit on a good quality PCB will improve the sound quality.
• Use a +25/-25V DC, 4A dual power supply for powering the circuit.
• K1 can be an 8 ohm, 50W loud speaker.
• IC1 must be fitted with a proper heat sink.

Description.
Here is the schematic of a 3 way active cross- over network circuit that finds a lot of application in audio amplifier systems. The heart of this circuit is National Semiconductor’s IC LF353 which is a dual JFET input operational amplifier with internally compensated input offset voltage. The IC LF353 has high bandwidth, low offset currents, and low input bias current due to the JFET based input stage.
The working of the circuit is very simple and straight forward. Two LF353 ICs are used here. The input audio signal is first buffered using the opamp IC2a and POT R7 can be used to adjust the gain of this buffer stage. The buffered audio input is then spited into three bands using the filters built around the opamps IC2b, IC1a and IC1b. IC2b handles the bass range, IC1a handles the mid range and IC1b handles the treble range.POT R22, R23 and R24 can be used to adjust the bass, midrange and treble respectively.

Circuit diagram.

Notes.

• Assembling the circuit on a good quality PCB improves the sound quality.
• The circuit cab be powered from a 12V DC supply.
• he ICs must be mounted on holders.
• The outputs OP1, OP2 and OP3 must be connected to the respective inputs of the multichannel power amplifier stage (not shown in circuit).

Description.
The circuit given here is of a 2 x 32 Watt stereo amplifier using the famous TDA2050V IC from ST Microelectronics. The TDA2050V is an integrated monolithic 32 watt class AB audio amplifier IC available in the Pentawatt package. The IC has lot of god features like low distortion, short circuit protection, thermal shut down etc.

Two TDA2050V ICs are used here, one for each channel. For each channel the input audio signal is fed to the non-inverting input of the IC through 1uF (Non-Polarized electrolytic) capacitor and this capacitor performs the job of DC decoupling. The ratio of the 22K and 680 ohm resistors determine the gain of each channel. The network comprising of 2.2 ohm resistor and the 0.47uF capacitor connected between the output of the amplifier and ground forms a Zobel network which represents the impedance of the speaker appear as a steady resistive load to the amplifier output and this dramatically increases the high frequency response.

Circuit diagram.

Notes.

• Assemble this circuit on a good quality PCB.
• Use 18V DC dual power supply for powering the circuit.
• Fit the ICs with adequate heat sinks.
• Connecting 10K POTs at input lines will serve as a volume control.
• For full output power the circuit require 200mVpp RMS input.

Description.
A lot of electronic circuits in the domain of audio amplifiers are already been published here. This circuit is a little different because it is a four channel amplifier. Each channel of this amplifier can deliver an output of 15Watts into a 4 ohm speaker. The amplifier can be operated from a single 12V DC supply and this makes it possible to use this amplifier in car audio applications too.

The circuit is based on the 15W BTL X 2 channel audio power amplifier IC TA8215 from Toshiba. Even though chip is specifically designed for car audio applications it can be also used for home audio applications. Two TA8215 ICs are used here in order to obtain a 4 channel amplifier system. The circuit is designed almost exactly as per the application diagram in the ICs datasheet. Pins 7 and 19 are the Vcc pins of the ICs internal integrated power amplifier stages and these pins are connected to the positive supply. Pin 9 is the Vcc pin for ICs internal preamplifier and it is also connected to the positive supply. Pins 13 and 14 are the internal power amplifiers ground pins and they are tied together and connected to the ground. The internal preamplifier’s ground pin (pin5) is connected to the common ground through a 10 Ohm resistor which makes the input ground separated from the common ground by a resistance of 10 ohms and this improves the noise rejection. The 100uF capacitor works as a power supply de-coupler. The resistor networks connected to the output lines of each amplifier improves the high frequency stability. The variable resistors (R3, R4, R12 and R13) works as the volume controller for the corresponding channels.

Circuit diagram.

Notes.

• Assembling the circuit on a good quality PCB is a must for obtaining optimum sound quality.
• Use 12V DC for powering the circuit.
• The ICs must be fitted with adequately sized heat sinks.
• R3, R4, R12 and R13 serves as volume controllers.
• K1 to K4 can be 4 Ohm, 20W speakers.
• This amplifier circuit can be used in a variety of applications such as car audio systems, home theater systems, personal audio systems, public address systems etc.

Description.
The schematic of an automatic cooler fan for audio amplifiers is given here. The circuit automatically switch ON the cooler fan whenever the temperature of the heat sink exceeds a preset level. This circuit will save a lot of energy because the cooler fan will be OFF when the amplifier is running on low volume. At low volume less heat will be dissipated and it will not trigger the cooler fan ON.

The temperature is sensed using an NTC (negative temperature coefficient) thermistor R2. Junction of thermistor r2 and resistor R1 is connected to the inverting input (pin3) of IC1 which is wired as a comparator. The non-inverting input (pin2) is given with a reference voltage using the preset R3. As temperature increases the resistance of NTC thermistor will drop and so do the voltage across it. When the voltage at the inverting input becomes less than that of the reference voltage (set for a particular threshold temperature) the output of the comparator goes high and switches the transistor Q1 ON. This will activate the relay and the cooler fan will be switched ON. When the temperature decreases the reverse happens. LED D2 will glow when the fan is ON. Diode D1 is a freewheeling diode.

Circuit diagram.

Notes.

• The circuit can be assembled on a Vero board.
• Use 12V DC for powering the circuit.
• The circuit can be calibrated by adjusting the preset R3.
• K1 can be a 12V, 200 ohm, SPST relay.
• LM311 must be mounted on a holder.