[sdiy] VCA distortion - bad

[René Schmitz]

Hi Michael,

It could be that the triangle is clipped at the opamp after the OTA.
Does the clipping depend on the CV? If so, then you should lower the CV 
instead. Or change the gain at the output opamp.

Cheers,
  René

Jim Patchell wrote:
>     You need to limit the signal at the input of the CA3080 to about 
> 10mV...so you need to let us know what your input voltage is...but, with 
> the values you show...200K-220, 10 volts would attenuate down to 10mV. 
> (the attenuation ratio of 200K to 220 ohms is about a factor of 1000).
> 
>     Several people have posted analysis of the OTA recently...mine is here:
> 
> http://www.silcom.com/~patchell/SecretsOfOTAs.pdf
> 
>     Another list member also wrote a very nice article on the OTA...I am 
> sure he will post his url himself...I hope (since I can't rembmer it, 
> lost all my bookmarks).

You mean the article from Achim Gratz, I have linked it from my homepage.

> Michael Ruberto wrote:
> 
>> I am using Bernie Hutchins' 3080 VCA circuit in my processor but I am 
>> getting distortion causing my triangle waves to become flat on top. I 
>> have changed the input resistor from 100K to 200K compared to the 
>> electronotes version of the circuit. should I have also changed the 
>> 220 ohm bias resistor following the input resistor? is there some 
>> calculation to determine these values?
>> the only other thing I changed from the original design was the 
>> feedback resistor in the output amp, I don't have 560K so I used the 
>> closest I had - 470K. I greatly appreciate any advice...
>>
>> ~M
>>
>> _________________________________________________________________
>> The new MSN 8: smart spam protection and 2 months FREE*  
>> http://join.msn.com/?page=features/junkmail
>>
>>
> 
> 
> 
> 

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159