Audio amplifiers from class A to T
The final amplifier is the power source of every audio installation. Its job is to convert a small alternating voltage into a powerful signal for driving loudspeakers with as little distortion as possible.
Delivering a large amount of power is not a simple task for an amplifier. Voltage amplification and current amplification are both necessary in order to provide sufficient power to speakers connected to the amplifier. To produce power amplification in a final amplifier, various concepts have been developed for using transistors or FET’s to generate high-quality output signals and to improve the efficiency of the output stage.
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VOX circuit schematic
VOX is a switch ordered by voice, often used at microphones instead of the classic switch button. The vox described here may be connected to almost any type of audio equipment which has an external speaker for coupling.
The threshold action is set with volume potentiometer of the audio amplifier which commands the VOX . The signal (on speakerphone) from the terminals of R2 is connected capacitive on T1 base. Resistance R3 limits base current of the transistor, in cases in which voltage input exceeds 600mV. Diode D1 hangs positive trip of the input signal, so Veb can not become less than 0.6V.
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PIC16F88 SWR meter
SWR or standing wave ratio is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum), in an electrical transmission line. The SWR is usually defined as a voltage ratio called the VSWR, for voltage standing wave ratio. For example, the VSWR value 1.2:1 denotes a maximum standing wave amplitude that is 1.2 times greater than the minimum standing wave value.
The swr meter circuit schematic we present can be used to powers up to 100W rf and can help you obtain the maximum power to antenna. Usually a transmitter is adjusted to the maximum power at the output but it must be matched with the antenna. SWR is an indicator of reflected waves bouncing back and forth within the transmission line, and as such, an increase in SWR corresponds to an increase in power in the line beyond the actual transmitted power. This increased power will increase RF losses, as increased voltage increases dielectric losses, and increased current increases resistive losses.
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