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Overview The circuit was constructed with the use of power audio amplifier LM380 in conjunction with the circuit that makes use of electronic soft switching and tone control. Terminology - Tone Control – electronic circuits used to modify an audio signal before it is provided to headphones, speakers, or recording devices by the use of amplifiers
- Amplifier – an electronic device used for intensifying the amplitude or power of a transmitted signal by manipulating the output to counterpart the input signal but with a larger amplitude
- LM380 – a power audio amplifier used for consumer applications with wide supply voltage range (10V-22V), low quiescent power drain (0.13 W), voltage gain fixed at 50, high peak current capability (1.3A), input referenced to GND, high input impedance (150K ohm), low distortion, and standard dual-in-line package
Circuit Explanation
A switch using the emitter follower pattern is consisted of a medium power BD131 transistor to act as the soft switch circuit to make sure that the power is developed steadily without the presence of any direct current blow, while the collector is attached to the permanent supply voltage. The power supply hum is filtered by the 2H inductor in series. A hum is an unwanted noise that is a by-product of most electronic devices. It can have negative effects on humans such as headaches, nausea, higher level of irritation and fatigue, sensory deprivation, and being disoriented. Adding the inductor in series is not as much necessary if the DC supply is sufficiently even. As the 10K ohm resistor and 10uF capacitor work together, they can serve as a hum filter by maintaining an efficient DC supply and ensuring that the full supply of transistor from 0 volts while the capacitor gradually charges.
When the amplifier turns ON, the LED1 will light and stays ON, but when it is OFF, the control voltage should be measured at 0 volts. There are two loudspeakers powered by the LM380 but the capacitor could release a rough intersect which will block the lower frequencies, thus making the loudspeaker act like a tweeter where high frequencies are produced at around 2,000 Hz to 20,000 Hz.
The tone control configuration circuit uses a very popular and most common form of active bass and treble Baxandall tone control circuit, which has a unity gain at midband and uses standard linear potentiometers. This provides the supply for the amplifier while the first BC109C transistor serves as a buffer with high input impedance and the second BC109C amplifies the losses from the tone control. the bass control is focused at 100 Hz while the treble control is focused on 10 KHz. The reactive connections of capacitor and resistors attenuates high and low frequencies. Application
The tone control can be used in several audio applications by adding to amplifiers as a stand alone control module. The LM380 2.5 W power aduio amplifier can be used in phonograph amplifiers, intercoms, line drivers, teaching machine outputs, alarms, ultrasonic drivers, TV sound systems, AM-FM radio, small servo drivers, power conductors and others. Source:www.zen22142.zen.co.uk/Circuits/Audio/2wamptc.htm
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