“The A/DA Final Phase was originally designed by Lee Powell in 1977. It
used Vactec opto-coupled resistors and a very unique phase shift
circuit along with a “one knob” distortion that keeps the level constant
with different amounts of distortion. When David heard it, he was
intrigued by the depth of the phasing. The original Final Phase design
was shipped for only a few months and replaced with a more stable and easier design manufacture using switched capacitors instead of the Vactecs
in 1978. This preserved the “high-Q” sound of the phaser and broadened
the sweep range.”
“The A/DA Final Phase is a 10-stage phase shifter with distortion. It
also has a random sweep modulator that modulates the sine wave, speeding
it up and slowing it down and adding sine waves so it sounds like a
I have no idea whether the above is true but it makes for an interesting read. Visit DiscoFreq’s for more information and photos on this effect.
These have been reissued and can be found at Analogman.