Friday, February 15, 2019

amp with mosfet output

Here is the circuit as designed.
I printed the schematic and taped it to a board. I thought I would drive a pin at each dot in the schematic. That cherry board as to hard so I drilled a hole at each dot and screwed a lug to it. Then it was just connect the dots with the parts.
It is very stable. No motor boating or whistling. I connect my fluke meter to the output on it lowest range and read .02 millivolts. I connected my AF generator and set the output to 5 millivolts then checked the input and it was less than a millivolt on the input. I set the meter to read db amd adjusted the input to -50db the output read about -20db. The reading were at different resistances but the meter would not read the signals at the low levels used in the test. (the reading are relative to the voltage drop at each point)  I connected a speaker from a telephone hand set and it was room filling volume. I think this one is the best so far. Maybe it will be put on a metal ground plane with a front panel for the input and output jacks, switch and volume control.

Note: A 2N7002 MOSFET should work. The other transistors are general purpose Germanium AF transistors. You could use silicon transistor but would need to adjust the bias.

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