[sdiy] Deciphering Roland 100 filter schematic

[Aaron Lanterman]

Howdy,

I'm meeting right now with my student Billy, who is working on making  
a version of the Roland 100 VCF:

http://fa.utfs.org/diy/roland100/101_op27.jpg

See the bottom half, 3rd "block" from the left.

1) There's a row of pots at the top of the filter (on the schematic),  
that is that have notations like "100kA" and "100kB". VR305 is like  
that too, it's marked "100 kB". Any ideas of what the A and B  
notations mean?

2) Several of the caps, such as C321, C322, C323 have notations on  
them like "10/16 N.p" and "100/16." I'm guessing N.p means "not  
polarized," but I'm not sure about the slash notation. What do those  
notations mean? They look like something from the mad hatter in Alice  
in wonderland. (Most of the other caps have microfarad markings.)

We're also trying to decipher the resonance pot. There's two variable  
resistors ganged together.

3) What do the circles that are tied to ground just below the variable  
resistors indicate?

4) Related to 3 - should we interpret the variable resistors as one  
end tied to a pot, another end tied to the wiper, and the other end  
left floating? Or is that ground marking somehow important?

5) I see what the "right" resonance pot is doing - it looks like it  
controls the amount of feedback to the negative part of the diff pair  
at the bottom of the diode ladder. But what is the other pot, the one  
that connects "A" and "B" (just to the upper right of FET Q314, which  
looks to be a buffer) doing?

5) Is VR305 a trim to adjust the DC bias point on the left side of the  
ladder to make it match that on the right? That's my intuition.

- Aaron