[sdiy] Interpreting four-pole-w-feedback circuits

[Aaron Lanterman]

On Mar 6, 2008, at 1:07 PM, Donald Tillman wrote:

>> Good eye!  You're right, the ARP patent drawing is in error.
>
> If you check the production schematic, you'll see the inversion.  See
> Joachim Verghese's ARPTech site for schematics of the 4072 and 4075
> modules with their diff inputs and how they connect up the resonance
> control.
>
> (The ARPTech pages are long gone, but I've kept an archive version
> here: http://till.com/arptech)

Interestingly, I can't find any actual examples of fourpole OTA-C  
circuits on that list... it's like they didn't actually use that  
patent. What I do see are a lot of these things using diff transistor  
paris and Norton amps, and Moog ladders (which I recall they had to  
stop using to avoid getting sued.)

Curious... what is up with the extra transistors in ARP's ladders? On  
the 4034 and 4035 they're labeled Z3A and Z4A. Wait - there's another  
odd one, Z2A. I don't think I've seen any other ladders like that.

- Aaron