Phase 90 - not phasing!

[MASTER VOLUME]

Hi there i have built a MXR Phase 90 using Hilbi's vero layout. I have made a few part substitutions ;
R5 3.9M - i have used a 3.7M.
Q5 2n4125- i have used a 2n3906.
C4 15uF - i have used a 22uf
Unmatched FETS -  J201.
The problem i have with it is that is not phasing. Neither the speed or trim pot have any effect on the sound.
I have checked the oscillator and that is working.
Here are some voltages;
IC1 - Pin 1- 4.81v
             2- 4.81v
             3- 3.25v
             4- 0v
             5 - 3.5-4.8v
             6 - 4.5-5.5v
             7 - 1.8 - 7.2v
             8 - 8.82v (batt +ve)
IC2 + IC3(SAME VOLTAGES FOR BOTH)
        Pin 1 - 4.81v
             2 - 4.81v
             3 - 4.71v
             4 - 0v
             5 - 4.7v
             6 - 4.81v
             7 - 4.81v
             8 - 8.82v

Q5        E - 4.81V
            B - 4.2V
            C - 3.04V

Q1-Q4 FETS   D - 4.7V
                     S - 4.81V
                     G - OV
Voltage across 5.1v zener - 4.81v.

I think the problem lies in the fets not being switch on/off by the oscillator and therefore not phasing ,as it is the circuit is just amplifing the input signal.
Any ideas , suggestions etc would be greatly apprieciated.
Thanks in advance.

[R.G.]

The J201 has a very small VGSoff parameter. That means, it takes only a little reverse voltage on the gate relative to the source to make it be completely off.

Your JFET sources are sitting at 4.81V, the gates are at 0V. So the gates are at -4.81V compared to the source, and so they are 100% fully off. There can't possibly be any phasing.

There is a trim pot in the standard design for raising the gate voltage up to near the sources to adapt for different JFETs.
(1) do you have the trimpot in there?
(2) does the trimpot have 4.81V on one side, 0V on the other, and does the wiper voltage change between 0 and 4.81 as you turn it?
(3) if so, do the JFET gate voltages change with the trimpot being turned?

[MASTER VOLUME]

DOH! There was a minute piece of solder between the gnd and the track that had the fet gates on it. It now works, although it sounds alot like a tremolo at faster speeds, is this normal for a phaser?

[MartyMart]

J201's = not the right fet for the P90, you need 2N5952's or possibly 5958's would work
They also ned to be matched for the best effect too !

MM.

[MASTER VOLUME]

HI there, just an update, the circuit works now and i have chosen 4 fets that sound good together(matched by ear),it sounds great and i can perfectly nail Pink Floyds Breathe, but there is a drop in volume when using the circuit. I have changed R10 to 180k and that helped a bit, but it is  still dropping volume when used.
Has anyone else had this problem and/or know a way of rectifying it ?
Thanks in advance - MV.

[boyersdad]

Why not add a buffer to the output?