stereo headphone amplifier.

stereo headphone amplifier.

LM4910 belonging to the Boomer series of National Semiconductors is an integrated stereo amplifier primarily intended for stereo headphone applications. The IC can be operated from 3.3V ans its can deliver 0.35mW output power into a 32 ohm load. The LM4910 has very low distortion ( less than 1%)   and the shutdown current is less than 1uA. This low shut down current makes it suitable for battery operated applications. The IC is so designed that there is no need of the output coupling capacitors, half supply by-pass capacitors and bootstrap capacitors. Other features of the IC are   turn ON/OFF click elimination, externally programmable gain etc.

Circuit diagram of the LM4910  stereo headphone amplifier is shown above.C1 and C2 are the input DC decoupling capacitors for the left and right input channels. R1 and R2 are the respective input resistors. R3 is the feed back resistor for left channel while R4 is the feed back resistor for the right channel. C3 is the power supply filter capacitor. The feedback resistors also sets the closed loop gain in conjunction with the corresponding input resistors.

Notes.

• The IC is available only  in SMD packages and care must be taken while soldering.
• The circuit can be powered from anything between 2.2V to 5V DC.
• The load can be a 32 ohm headphone.
• Absolute maximum supply voltage is 6V  and anything above it will destroy the IC.
• A logic low voltage at the shutdown pins shut downs the IC and a logic high voltage at the same pin activates the IC.

Specifications

20W Bridge Audio Amplifier kit, based on the TDA2005 IC, a class B dual audio amplifier, specifically designed for car radio applications etc.


Power supply - 18 VDC

Output power - 20 W, 4 ?

IC built in Thermal Shut-down, Load dump voltage surge protected

Terminal pins for connecting left and right audio signal inputs

Relimate Connector for connecting Potentiometer (POT) for volume adjustment

Power Battery Terminal (PBT) for easy power supply and speaker connection

Power-On LED indicator

Heatsink for IC

Four mounting holes of 3.2 mm each with nut and stud

PCB dimensions 63 mm x 65 mm


schematics 

component list

pcb

long range FM transmitter

The use of transmitters which have a more powerful output than the ‘flea-power’ are sometimes required when there are many obstacles in the path of the surveillance transmitter and monitoring station receiver, or the distance between them is too far so as to make a low powered device feasible. Whereas a typical micro transmitter will produce an RF power in the order of just a few milliwatts, i.e. a few thousandths of a watt, the VHF-FM transmitter described has a power output of between around a half and 2 watts, depending on the power source, which may be anywhere between 6 volts and 30 volts d.c. The battery or batteries should be of the alkaline high power type, since the current drain will be found to be relatively higher when compared to microtransmitter current drain. The power output of this device is somewhat proportional to the current drain and so therefore both may be decreased by altering the value of R6 to a higher resistance, or a variable resistor with a value of around 1k may be introduced in series with the existing R6, so as to give a variable power output. The variable resistormust not be a wirewound device because this would act as an inductor which will cause feedback problems.The audio input to the power oscillator, which incidentally is formed by TR2 and associated components, is derived from a piezoelectric microphone which drives the simple audio frequency amplifier TR1. The input of the audio amplifier is controlled by the gain pot R1, which selects the correct amount of voltage that is generated by the piezoelectric microphone, then connects this signal to the base of audio amplifier TR1 via C7. It may be found that there is insufficient housing space for a bulky piezoelectric microphone, so with a slight modification to the circuit, it is possible to employ an electret microphone insert as shown. Since the RF field that is generated by this transmitter is relatively large, the problem of RF feedback may very well be encountered. This may be overcome by placing the transmitterinside a metal enclosure, keeping all internal wiring as short as possible and the aerial wire.

Component listing for 1 watt transmitter

Resistors Semiconductors R1 = 27k TR1 = BC547 R2 = 330k TR2 = 2N2219 fitted with heat sink R3 = 5k6 MIC = piezoelectric microphone R4, 5 = 10k R6 = 100R

L = 6 turns 22 gauge enameled wire wound on 3⁄16″ former

Capacitors

C1, 2, 3 = 330 pF C4 = 2–10 pF trimmer C5 = 4p7 C6 = 1 nF

C7,C8 = 40uF/25V Electrolytic

Circuit diagram for Long range FM Transmitter

simple AM transmitter

Here is the circuit diagram of a simple AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited  power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs.You will love this!.
The circuit has two parts , an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz. These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again. The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground. Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistance R5.

• The transmission frequency can be adjusted using the variable capacitance C3.
• Use a 200uH inductor for the L1 in the tank circuit.
• Power the circuit using a 9V battery for noise free operation.
• Use a 30 cm long insulated Copper wire as the antenna.

Am Transmitter Circuit Diagram with Parts List

10W Mini Audio Amplifier

here i'm gone to post a article about how to built a audio amplifier at your home..
ummm...if u have basic knowledge then its a quite simple 4 u....

component list


R1  6 Ohm
R2  220 Ohm
R3  nothing
R4  10 KOhm pontesiometer
C1  2200 uF  25V
C2  470 uF  16V
C3  470 nF  63V
C4  100 nF
C5  nothing
C6  nothing
IC1  TDA 2003

PCB LAYOUT

COMPONENT LAYOUT

HOW YOUR AMPLIFIER LOOKS LIKE