Monday, January 26, 2015

DC Coupled Audio Amplifier

Designs for audio amplifiers with DC coupling to the load are not often encountered these days, even though they offer definite advantages. One advantage is that there is no need for the complication of a second (symmetric) power supply; another is good frequency and phase response. Also, no special electrolytic capacitors are needed for voltage stabilisation, and switch-on ‘thump’ is much reduced. To try to rescue this class of circuit from obscurity the author has designed a headphone amplifier working along the lines illustrated in Figure 1.

DC-Coupled Audio Amplifier Circuit Diagram



It consists of a voltage divider, a voltage follower and the loudspeaker in the headphones, whose other side is connected to the junction of two electrolytic capacitors, providing the virtual earth. The potential at this point is, of course, half the supply voltage. All we need to do now is suitably couple in the audio signal to be amplified. Figure 2 shows a practical realisation of this idea in the form of a stereo headphone amplifier. The amplifier itself consists of IC1 and P1, R3 and R4 (giving a gain of 11).

DC Coupled Audio Amplifier Circuit Diagram


This part of the circuit demands no further explanation, and the same goes for the voltage divider mentioned above, formed by R1a and R1b. The signal is coupled in via the potentiometers. C2 and R2 have a special purpose: C2 connects the bottom end of the potentiometers (ground for the input signal) to the virtual earth. However, this capacitor creates a feedback path which can lead to oscillation of the amplifier under some circumstances. R2 damps this tendency to oscillate.
 
It is possible to calculate suitable values for these components, but it is better to determine them by experiment. C2 must be sufficiently large that stray electric fields do not cause unacceptable hum at the output. R2 must be sufficiently large that the voltage at the amplifier’s virtual earth stabilises quickly enough after switch-on. The polarity of the electrolytic is unimportant as no significant voltage appears across the network. It is possible to try the circuit out with the C2/R2 network shorted and observe the behaviour of the circuit at switch-on using an oscilloscope. Depending on the degree of asymmetry in the circuit, the voltage at the virtual earth point can take a considerable time to stabilise.


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Tuesday, January 6, 2015

Audio Stereo Power Amp Circuit

audio-power-amp-schematic

This is a 50 Watt Audio power amplifier circuit based single IC STK4036II. Use heatsink to prevent overheating on the IC. 

The amplifier circuit will give you good quality of sound unexpensive and have low price. 

It is easy we make a power amplifier using only few external components. 

The STK4036II amplifier are will find in enough eponymous stereo amplifiers , but also in enough activety loudspeakers. 
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Friday, December 12, 2014

Phone ringtone generator circuit


ringtone-generator-schematic
This is a simple home telephone ringtone generator circuit which is built with applying only several electronic components / parts.It generates simulated telephone ringtone and requires only DC supply with 4.5V DC to 12V DC voltage.One may possibly use this circuit in ordinary intercom or phone-type intercom. 

The sound is pretty loud when this circuit is operated on +12V DC power supply. Even so, the volume of ring sound can be adjusted.
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Battery Indicator schematic diagram


This circuit diagramc shows a simple battery level indicator.In general, in mobile phones, the battery levels is displayed in dot or bar style.This helps you to effortlessly acknowledge the battery level.
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6 Input Mixer


mixer-6-input
 
A simple mixer with 3 line inputs and 3 mic inputs using commonly available parts. 
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Rain Detector schematic

Here's a simple rain detector circuit. It uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.
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Lead Acid Battery Charger

Except for use as a normal Batter Charger, this circuit is perfect to 'constant-charge' a 12-Volt Lead-Acid Battery, like the one in your flight box, and keep it in optimum charged condition. This circuit is not recommended for GEL-TYPE batteries since it draws to much current. The above circuit is a precision voltage source, and contains a temperature sensor with a negative temperature coĆ«ficient. 
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