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FET Preamplifier circuit

2015-01-01 07:15  
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Field Effect Transistor is an amplifying device in which the output current depends on the input voltage. The FET Pre Amplifier described here is a sensitive and stable Preamp circuit using an N-Channel FET and a PNP Bipolar transistor. This combination gives high input impedance and low output impedance with stabilized gain.TheJunction FEThas a conducting channel .It’s one end is theSourceand the other end isDrain.The junction FET has direct ohmic contact at the gate. The enclosing material forms theGate. If the channel is formed ofN- materialand the gate is formed ofP -material,the FET is called asN-channel FET. If the arrangement is of the opposite type, then it is called asP-channel FET. The conductance of the channel can be controlled by the Gate-Source potential and then current flows from drain to source.

FET Pre Amp Circuit diagram


BFW11 Datasheet
The circuit is asensitive preamplifierusing an N-ChannelFETand aPNP transistor. This combination gives high input impedance and low output impedance with stabilized gain. Anygeneral purpose PNPtransistors likeBC 557orBC558can be used according to the required gain. The gain of the Preamp depends on the Feedback network and with the given values of R4 and R5, it is around 20. Input of the preamp is sensitive and readily matches with microphones and ceramic pick up.


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