Uranus phaser

[R.G. Keen]

Re your six stage - 

Good work on the phaser. A few suggestions from my tinkering with 
vibe clones (I probably drew up the schematics you refer to). These are 
all in the spirit of gilding the lily... 

- The six-LDR module is a good idea. Since it is a replaceable module,
you might try using just enough heat-set glue to hold the LDR's in
place, then putting a shiny-inside cover over the top of the whole
mess. The reflections inside the "light cavity" do a good job of mixing
and leveling the light amplitude. This is why the original has a
shiny-inside cover, I think.

- You can get MUCH faster LDR's. Your slow-sweep applications may not
need them, but faster ones won't hurt you, either. You can test the
LRD's for speed by rigging up a light-tight tube with an LED inside and
a hole to press the LDR into. Drive the LED from a pulse source at
about 1- 10 Hz, and use a resistor in series with the LDR to a voltage
source. Monitor the drive to the LED and the voltage across the LDR.

This gives you the turn-on and turn-off slopes directly on an
oscilloscope. You can also sort them by resistance per unit light this
way, as the LED light does not vary much from one LDR to the next, and
so the voltage across the LDR is a direct measure of the relative LDR 
resistance. Again, this may not matter in your application, but does
for people who want to place the phase notches exactly.

- Typical CdS LDR's are most sensitive to green light, just like the
human eye. Using a green LED, especially an ultra-bright green LED,
will make the current used to drive the LED much lower. 

By the way, I did finally hear a reasonable suggestion for why the
univibe has the phasing capacitor values staggered like it does, which
had always mystified me. The original 'vibe also had a "Vibrato"
setting. If you set the caps to all the same value, the phase shift is
all concentrated in one spot. With the large staggering of phase shift
values, there is some phase shift at the top and bottom end of the
audio spectrum to provide vibrato even at the extremes of the swing.
That made far more sense than any other explanation that I had heard or
could come up with.