Bias: favorite BJT/JFET bias guide
Collector-feedback bias
@8/14 2012
ss9014, beta~=300
MIC pre amp: @2014/7/7
Rc=R1= 3.3k, Rb=R2=900k
Vc= 1/2 VCC
9018, Hfe~=100-120
R1=2.2k, R2=180k,
Vc = 5.7V@13V VCC (Ic=3.3mA, Hfe~=118)
R1=680R, R2=36k,
Vc = 7.2V@13V VCC (Ic=8.5mA, Hfe~=46)
JFET zero gating bias
Gate is grounding. focus on R4 selecting.
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MPF102
Vgs(off) = -8V
typical Idss= 2mA to 20mA ( i guess most of in range 2mA to 5mA, sometime, you need checking this)
R4=680R
Vgs= -Vs= 1V Id=1.5mA @Idss=2mA
Vgs= -Vs= 1.9V Id=2.9mA @Idss=5mA
Vgs= -Vs= 2.5V Id=8mA @Idss=8mA
R4=1.6k
Vgs= -Vs= 1.9V Id=1.2mA @Idss=2mA
Vgs= -Vs= 3.1V Id=1.9mA @Idss=5mA
Vgs= -Vs= 3.7V Id=2.3mA @Idss=8mA
R4 = 2.7k
Vgs= -Vs= 2.5V Id=1mA @Idss=2mA
Vgs=-Vs=3.8V Id=1.4mA @Idss=5mA
Vgs=-Vs=4.4V Id=1.6mA @Idss=8mA
R4=3.3k
Vgs= -Vs= 2.8V Id=0.8mA @Idss=2mA
Vgs= -Vs= 4.0V Id=1.2mA @Idss=5mA
Vgs= -Vs= 4.6V Id=1.4mA @Idss=8mA