[sdiy] 3080/13700 OTA question

[Ian Fritz]

Tim --

Clearly an error on the drawing.  My guess would be that the 10k and 2.2M 
resistors are swapped.  this would give you envelope time up to a few 
seconds and 1.5 mA of Iabc.

Ian


At 03:35 AM 1/2/2009, Tim Ressel wrote:
>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
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