Maxon noise gate problem

[Kipper4]

I built the Maxon noise gate (ahem) the details are on the other forum (just search noise gate)
It's passing audio but not gating. Its always open
I dont get how it gate but thats beside the point i feel at this stage.
Because I've substituted the perscribed fet (2SK30) with a 2N5457 i read that it may need to be biased differnatly
please suggest which values i need to change or a remedy to make it gate
thanks and Sorry Aron
Rich