Messages

I just edited my original post. I meant 5x not 50x. I was thinking of 50mv. lol
There was a model for the ideal 2N5952 in Tina so I used that. I found the voltage at its base 130ish Hz notch and adjusted the gate until the notch began to move and then used that as a starting point. I then gradually changed the voltage until the notch was up at 2khz and that was about 250-300mv, which is the swing voltage from the LFO that reaches the gates. I then just replaced the jfet with a j113 in the sim and did the same. It was about 50mv of difference on the gate to produce the same effect. So I reduced the R and C impedances to a 1/5 of what they were in the sim and it was pretty close. then I just translated that to the components on the board.

I don't have the vgsoff for the j113s I'm using no, but I used the op amp jfet matching circuit that is available, and they are all about 0.95v gs to produce a 10k resistance.

<edited - I meant to say 5-6x more sensitive not 50x lol>
I just built myself a phase 90 clone using j113. I was a unhappy with some of the tone (and clipping distortion) I was getting so I used Tina sim to simulate the difference between the "ideal" (ha) versions of each jfet. I swept the notch up and down and discovered that that (according to the sim) the j113 is about 5-6x more sensitive across the parallel 22k than the 2n5952. the LFO voltage swing reaching the fet gate is about 250-300mv peak to peak, but I can make the whole j113 sweep in about 50mv. So to compensate I changed each of the parallel resistors for 4.7k and the 47nf caps on the non inverting input to the filter sweep op amps were changed to 220nf (to keep the filter frequency in the same place).
I'm much happier with this sweep tone, although its still clipping a bit. I think its due to the PNP collector voltage being too high, so its not swinging in the center of its range. I'll drop the collector resistance further (at 10k compared to original 56k atm) and let you know how I get on.
Also the 10k in series with the zener isn't enough to properly reverse bias the zener, so I used a 1k to give it enough current. I'm using a psu not a battery so I'm not bothered. It still only draws 6mA ish anyway which is hardly a lot.
Steve