Bi Phaser questions

[Kipper4]

First off here's the gubbins

http://www.ozvalveamps.org/repairs/circuits/stomps/biphase.gif

questions
1 What is the 100nf cap doing in the top left corner?

2 What are the 3x 100pf doing? tone shaping? Low pass filter?

Thanks guys

bonus question.
My guess is that the 22k's to Gnd on the phaser stage outputs, limit the least resistance that effects the stage.
Right or wrong ?

[Mark Hammer]

Near as I can tell, the 100nf cap in the upper left corner is simply for smoothing out the LFO a bit.

The trio of 100pf feedback caps is to keep the noise that occurs with feedback in check.  You will note the 22k resistor between the output of stage 4 and inout of stage 2.  That provides modest feedback (high feedback would have been 12-15k).

And yes,  the 22k resistor combines with the drain-source resistance of the corresponding JFET to set the lowest notch location.  Assuming the JFET has infinite resistance, 22k and .047uf gets us maximum phase shift for each stage starting at 154hz.  As the JFET resistance drops, the combined parallel resistance of the JFET and 22k moves that location upwards.

[Kipper4]

Brilliant thanks Mr H