[sdiy] New OTA

[jays at aracnet.com]

>From the data sheet these seem to be log based since they are -33mv per dB. Am I missing something? Any way to control these exponentially for filters or linearly for CV VCAs?

Jay S.


John Blacet wrote:

> You need to study the data sheet here. This is actually well planned or 
> a lucky accident.
> 
> Use an inverting op amp stage to sum (100Ks) your front panel pot and 
> jack CVs. (Standard stuff).
> 
> Add one more 100K to add -10V to the mix. This should be an accurate 
> stable voltage (LM4040 for example). Also use the inverted 10V (+10) for 
> the pot leg 3.
> 
> Select your feedback resistor for the desired control range, such as 33K 
> for 100 dB.
> 
> Now everything goes the right direction. You needed the summing amp 
> anyway! The stable voltage reference is a plus since it can be processed 
> for use elswhere in the module. You need stable and accurate since the 
> control is 33mV/dB.
> 
> Aaron Lanterman wrote:
> 
> >
> > On Tue, 26 Jul 2005, John Blacet wrote:
> >
> >> You can do just about anything that you need to do OTA wise with the 
> >> Analog Devices SSM2164. Quad for under $4 each. Still production in DIP.
> >
> >
> > Reading over the 2164 data sheet, am I imagining things or does the 
> > control go the wrong direction? (I remember Dr. Mabuse mentioning 
> > something about that).
> >
> > - Aaron
> >
> > ----------------------------------------------------------------------------- 
> >
> >
> > Dr. Aaron Lanterman, Asst. Prof.       Voice:  404-385-2548
> > School of Electrical and Comp. Eng.    Fax:    404-894-8363
> > Georgia Institute of Technology        E-mail: lanterma at ece.gatech.edu
> > Mail Code 0250                         Web:    
> > users.ece.gatech.edu/~lanterma
> > Atlanta, GA 30332                      Office: GCATT 334B
> >
> >
> 
> -- 
> Regards,
> John Blacet
> 
> Blacet Research
> http://www.blacet.com