D104 & J-FET Impedance change schem


The D-104 Microphone W1CKI

Here is a neat way to make your D-104 sound like a $300 mic…or maybe better if you are running a old boat anchor.

This circuit was shown to me by K1DEU and is used by many AM’ers. It is an impedance changing circuit and allows the D-104 to see a high impedance, R1 25Meg.  The output of the NJFET is low impedance . Very little gain is developed with this circuit.

Note the 270k input resistor R5 in the grid of the existing pre-amp. The mike input of a 12AU7 connected to the  JFET output will only need about a 270K resistor for the grid resistor.

R7 and R2 can  be used to "EQ" the audio, giving up to 6db bass or treble cut.



Back To W1CKI Home Page


















This Web Page Created with PageBreeze Free HTML Editor