So this started in my "vocal megaphone effect" thread but led to the 3320 chip which allows you make 4 pole filters. Thanks to all for the response on that thread. So I am making a 4 pole highness. But I have lots of questions. On the breadboard it makes a high pass but the Frequency and Resonance controls have no effect that I can discern. I am probably messing up some basic things but here I go.
Here is the Druid's redrawing of the data sheet circuit (actually the compatible CEM3320)
I am running this on single supply 9v. I just put a voltage divider (two 100k resistors) to give a midpoint voltage to the ground pin. I see the spec sheet says:
Voltage at negative supply pin: min -2.4v max -2.9v
So the midpoint voltage should be only 2.5ish?
I though about a buffered midpoint voltage but not yet tried it.
It has been stated the Freq and Res controls are really current and not voltage inputs. The spec sheet says:
Input bias current Freq control: min .2 max 1.5 micro amp.
Input impedance of Resonance control input min 2.7 max 4.5k
It also says:
sensitivity of pole freq control scale:57.5-62.5 mv/decade
I am told the Freq is a current input which should be thought of as "zero ohm" impedance. The schematic shows a 100k resistor from the CV to the pin...
To get inputs on the order of a micro amp I think need resistance on the order of (for 9v) 9M ohm. That can't be... So I tried a 1m pot feeding the 100k resistor both as a variable resistor and as a voltage divider but did not hear anything happening. I know I'm in the dark.... Should the control V start form 0 or the midvoltage/ground?
