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The circuit described here is based on the superior characteristics of dual-gate MOSFET (metal-oxide semiconductor field-effect transistor). It exhibits a very high input impedance that lends for good sensitivity and very less loading of the input signal source. Low cross-modulation characteristic leads to minimal distortion of the output with respect to the input signals. Also, the MOSFET offers low feedback capacitance and high transconductance. All these advantages make the MOSFET the most effective for high-quality mixer and converter applications. This dual-input audio frequency mixer circuit employs a single dual-gate MOSFET 3N200. One may, however, substitute it with any other dual-gate.  MOSFET such as 3N187 and BF966. (It is to be noted that BF966 is not gateprotected and hence calls for suitable precaution in handling it.) The audio frequency (AF) input from the first channel (CH1) is applied on gate 1 (G1) of the MOSFET through 500- kilo-ohm potentiometer VR1. The AF input f...

This amplifier is designed to be as flexible as possible, with no bad habits. Indeed, it will operate stably with supply voltages as low as +/-5V (completely pointless, but interesting), all the way to the maximum supply voltage of +/-70V. The only change that is needed is to trim the MOSFET bias pot! With the full supply voltage of +/-70V (which must not be exceeded!), RMS power is around 180W into 8 ohms, or 250W into 4ohms. Short term (or "music") power is typically about 240W into 8 ohms and 380W into 4 ohms. Note that depends to a very great degree on the power supply, and a very robust supply is an absolute requirement for tThe maximum output. In general, unless you really need the maximum possible power, I suggest that you limit the supply voltage to ±56V using a 40+40V transformer. You will get around 150W into 8 ohms from this supply voltage (short-term), but you also relax the demands placed on the MOSFETs and heatsinks. It is worth noting that a MOSFET amp will alw...