[sdiy] Phase shifters & Compandor chip availability

[eq927 at freenet.carleton.ca]

Hi Tim,
I've also built a couple of modified Quadra phasers similar to JH's 
design. JH has (had?) a good write-up on the very questions you ask on 
his website. The compander serves two purposes  - one is noise reduction 
- the other is to balance the clipping level of the diode soft limiter 
with the input audio signal in order to provide a pleasant (not 
speaker-blowing) mellow self-oscillation at high regen settings. Aside 
from the ladder design and compander, the phaser is a bit unusual in 
that the main output is in inverse mode (eg. n notches, n+1 peaks), 
giving a hollow band-limited sound at high regen. The first unit I built 
 worked first try, with randomly selected CA3046. The second unit 
distorted, and this was traced to a CA3046 where the Vbe of one of the 
transistors was markedly different from the rest. The compander design 
used in the Quadra is superior to the NE570/NE571 (both in performance 
and parts availability).
Regards, Mike