simplest voltage-feedback jfet op amp, gain of 10
vsupply+ vdd 0 dc 15V
vsupply- vss 0 dc -15V
v1 vin 0 dc 0 ac 1 sin 0 0.1V 1kHz
x1 vin vfb vdd vss 0 vout opa
r1 vfb 0 200
r2 vout vfb 1.8k
.subckt opa + - v+ v- vgnd out
j1 j1d + vs lsk170a
j2 v+ - vs lsk170a
* trim rs for zero dc offset
* rs trim = 3.451k (as if connected to vss bypassing servo)
rs vs vsv 1.8k
rbe j1d v+ 360
cc j1d v+ 47n
q1 out j1d v+ 2n3906 
rl out v- 2k
* bias servo
r1s vgnd vni 330k
c1s vni voi 330n
* ideal op-amp model ok for servo
eu1 voi vgnd out vni 1e5
r2s voi vsv 750
c2s vgnd vsv 430u
r3s vsv v- 560
.ends
.include ./lsk170.txt
.include ./models1.txt
.end
.control
op
setplot op1
print vout
noise v(vout) v1 dec 25 20Hz 20kHz
setplot noise2
print vdb(onoise_total)/2
ac dec 25 10Hz 1gHz
setplot ac1
plot vdb(vout)
.endc