[sdiy] some diy: ssm2040 filter

[René Schmitz]

Hi Ryan,

ryan williams wrote:
> first:  once the cutoff CV gets to a certain point (almost full CV) 
> there is a glitch and an audible pop is heard.  looking at the scope.  
> the ouput waveform starts to decrease in amplitude just before the pop. 
> when the pop happens the amplitude returns to the level it should be.  
> it makes no difference how quickly I change the CV.

Try adding a 1n (or thereabout) cap from the inverting input to the 
output of U2B. Maybe that expo is starting to oscillate at some point. 
(It's missing on my schemo too, sorry!)

> second:  the DC offset at each stage's output changes about 3.5V as the 
> OTA bias current is increased.  Actually, this change is only happening 
> at stages 1 and 3.  stages 2 and 4 have a small change, something like 
> .2V.  I expect this is because of the asymetrical distortion of each 
> stage. I'm measuing this with 0V input signal.  Is this normal? I think 
> that is way too much to be normal.

No idea there, I would have to measure that.

Cheers,
  René

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