AS3320 Filter Help

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dr.earlfunkton
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AS3320 Filter Help

Post by dr.earlfunkton » Thu Sep 05, 2019 2:29 pm

Hey Y'all!
I'm trying to build a stereo multimode filter bank based on the AS3320 chip (CEM3320 clone). I have some questions about the Resonance CV and Frequency CV. On the datasheet those points appear to be inputs for control voltage. How could I use a pot to control these spots? I imagine I could just wire up a supply voltage to the wiper of a pot and have one leg go to ground and the other to that input spot. Any flaws in my thinking?
Thanks in advance for any help!
Heres the datasheet i'm referencing:
http://www.alfarzpp.lv/eng/sc/AS3320.pdf

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devinw1
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Post by devinw1 » Thu Sep 05, 2019 2:49 pm

You got it. 200K resistor in line with the wiper of the pot to the resonance pin should be a good starting point.

dr.earlfunkton
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Post by dr.earlfunkton » Thu Sep 05, 2019 2:58 pm

devinw1 wrote:You got it. 200K resistor in line with the wiper of the pot to the resonance pin should be a good starting point.
Any idea of how much voltage I should supply to these points? I feel like it should be on the datasheet but maybe im blind.

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Post by devinw1 » Thu Sep 05, 2019 4:11 pm

dr.earlfunkton wrote:
devinw1 wrote:You got it. 200K resistor in line with the wiper of the pot to the resonance pin should be a good starting point.
Any idea of how much voltage I should supply to these points? I feel like it should be on the datasheet but maybe im blind.
It's a matter of current, not voltage, since you are feeding a gain cell with a control current. The original CEM datasheet talks a bunch about it http://www.bustedgear.com/images/datasheets/CEM3320.pdf, but does say that the pin 9 is at a potential close to ground and has 3.6K input inpedance. I can't find the max current, but I wouldn't go more than probably 150 uA. If you wire your control pot up to 12V and use a 100K resistor, you will be at around 115uA and be just fine.

dr.earlfunkton
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Post by dr.earlfunkton » Thu Sep 05, 2019 5:26 pm

Cool i'll try it out. If I were to make a stereo unit would I just double the schematic? Also could I control both channels at the same time if I had a stacked pot?

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Post by nigel » Fri Sep 06, 2019 7:43 am

dr.earlfunkton wrote:Cool i'll try it out. If I were to make a stereo unit would I just double the schematic? Also could I control both channels at the same time if I had a stacked pot?
You don't need to duplicate the pot, just feed the same control voltage to both circuits.

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devinw1
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Post by devinw1 » Fri Sep 06, 2019 10:11 am

Right, you just need a input resistor for each chip, and feed it the same CV.

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