MOSFET Audio Amp Projects

Written by tony oldhand
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MOSFET Audio Amp Projects
Transistors make a variety of amplifiers possible. (four transistors image by Eugene Tokarev from

Transistors are a common component in many amplifier designs. One special kind of transistor is called the MOSFET, which stands for Metal Oxide Semiconductor Field Effect Transistor. Many configurations of MOSFET amplifiers exist, since this is a versatile transistor. The MOSFET transistor is very efficient, lending itself well to small yet powerful audio amplifiers.

MOSFET Driver Amplifier

Three students at Worcester Polytechnic University designed an amplifier that uses MOSFETS as the main drivers. This means the MOSFET transistors are used as the main amplification source, changing low voltages into high voltages. They used common off-the-shelf components to design their amp. The result was an amp with 90 per cent efficiency, and a distortion of less than 1 per cent. Distortion is not good in an amp, since it detracts from the main signal, producing a raspy sound instead of a clean sound.

Combination Amplifier

A combination amplifier circuit is possible. Since many audio purists prefer the sound out of a tube instead of a transistor, a tube is used in the circuit. A special kind of amplifier, called the Borbely Tube-MOSFET circuit, does just that. The tube part of the amp is actually a preamp, taking the raw weak input and converting it to a higher voltage. MOSFET transistors take the output voltage from the tube, and amplify it even higher for the final output.

Delta Sigma Amplifier

Another amplifier configuration is the Delta Sigma amp. In this configuration, the MOSFET power transistors are wired in parallel. This means that two inputs are wired together, and this configuration is also called a "push-pull" amplifier. When one transistor is pushing out a high voltage signal, the other transistor is pulling in a low voltage signal. They alternate accordingly, and produce a common high voltage output signal.

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