[sdiy] 3080/13700 OTA question

[Tim Ressel]

Hi all,

I tried to implement the 3080 VCA from Lancaster's Music Modules as seen in the CMOS Cookbook. It has a simple envelope generator that idles at the negative rail and rises to 0 volts for full on. A resistor divider brings the voltage range down to about 2.8 volts above the negative rail. So far so good. The problem is this: the voltage divider is a 2.2 meg and a 680K resistor. It seems to me these high values cannot generate enough current for the Iabc input of either part. Other 3080/13700 circuits I've seen places the Iabc current at about 0.1 to 0.4 mA max. What am I missing here? 

Thanks in advance.

--Tim Ressel