Yes, for n-channel, Vgs=0 (OFF), Vgs=Vp (ON). Pick a low on resistance, high pinch-off N-channel JFET such as a 2N4859. Hal Chamberlain's VCO in M.A.M. drives this with a 100ns -15 V pulse , LM311. > On Jan 10, 2019, at 2:41 PM, Tim Ressel <timr at circuitabbey.com> wrote: > > So I would need a negative voltage to turn on a jfet, yes?