The famous Fetboy (Hamptone) Microphone Preamplifier.
Layout updated with 2k multi-turn trimmers to set the working point of the J-FETs. MPSA14 and BD139 used in working prototype.
Layout was made for transformers I had laying around.
Coupling capacitors can be changed to anythin from 10uF-47uF electrolytes. The poly capacitor is really not necessary.
About 26dB of gain.
Set 4V at the 100Ohm resistors (R8, R14) with the 100k trimers (R7, R13). Then set working point using a generator and osciloscope and the 2k trimers (R19, R20).
FETBOY (Hamptone) Microphone Preamp
Eagle 5 files availible for download. Supply PCB for a 24VAC transformer included.
