[sdiy] Resistor matching in Bergfotron complex VCO

[mark verbos]

I'm with Don on this one. Even with unmatched transistors and 1%  
resistors, the symmetry in all the ones I have build is pretty close.  
In the Buchlas, he didn't use that tightly matched resistors. The  
259's trimmer goes through a 10M resistor to ground and the 208  
doesn't even have a trimmer. I'd recheck the build. Be sure there's a  
FET input OP Amp in the integrator.

Mark





On Apr 27, 2008, at 11:28 AM, Donald Tillman wrote:

>> From: Aaron Lanterman <lanterma at ece.gatech.edu>
>> Date: Sun, 27 Apr 2008 04:57:47 -0400
>>
>> One of my students, Greg, is working on building the Bergfotron
>> version of the Buchla 259 triangle core.
>
> Hey Aaron,
>
> He'll need a large stock of colorful inks to do that!   :-)
>
>> At higher frequencies, it looks pretty triangular, but at low
>> frequencies it's more like a 20% triangle. (Also, when twisting
>> various knobs to get the lowest frequency, it seems to only get
>> down to 600 Hz, but I suspect that will be fixed once we get the
>> triangle more triangular.)
>
> Hey, at high frequencies *everything* looks triangluar.  :-)
>
> A slight resistor mismatch wouldn't cause that; I strongly suspect a
> wiring error.
>
>   -- Don
>
> -- 
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
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