SV: [sdiy] Buchla modifications

[karl dalen]

1: Let them ponder on how to make the trianglewave bipolar
and the square polar ""without"" adding any components! :-)

2:To remove components and still have the core up
  and working could be a neat brain wrestler.

KD

--- Aaron Lanterman <lanterma at ece.gatech.edu> skrev:

> 
> Another of my students (Manu) is working on building a Buchla-style 
> triangle core VCO.
> 
> I did an evil thing on my midterm quiz, which is I gave them the Buchla 
> 259 exponential converter schematic to analyze - in Buchla's original 
> handwriting. Uhm... this didn't go over so well, and required a lot of 
> during-exam clarification. Not a good idea on my part. I still feel guilty 
> about it.
> 
> So, I didn't really want to throw the Buchla 259 schematic at him to work 
> from, lest he immediately try to set it on fire. I suggested he try 
> hacking at the Bergfotron triangle-core (if nothing else since it's a 1 
> V/oct converter):
> 
> http://hem.bredband.net/bersyn/VCO/VCO%20Buchla%20core.gif
> 
> Part of the way my final project is structured is that their final design 
> can't be purely an existing design - they must modify it in some at least 
> vaguely interesting way.
> 
> Manu has the original Bergotron up on the breadboard. It's not working 
> yet, but I'm sure he'll get it working, right Manu? :)
> 
> Anyway... I'm less picky about fancy modifications here, since VCOs are 
> inherently such finniky beasts.
> 
> Anyone have a favorite modification the've wanted to try but haven't had 
> time to?
> 
> I was thinking of (not sure if any of this would change the performance or 
> not)
> 
> * Use the allegedly superior LM319 (it's what Paul uses in his VCOs) 
> instead of the LM311.
> 
> * Use the higher-input-impedance CA3140 instead of the TL072 as the 
> integrating op amp
> 
> * Both of the above...
> 
> I want to keep the four-BJT-OTA (vs. replacing it with a LM13700 or 3080, 
> as Mark did), since I want to be able to use an NPN pair in the expo 
> converter.
> 
> I gave him a CA3083 for the expo converter (Ian often recommends it), and 
> was thinking the spare transistors could be set up as a "heater" as in Q3, 
> Q4, and A2 of Figure 1 of the AN-299 ap note:
> 
> http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/opamp/AN-299.pdf
> 
> Any other assorted ideas of easy but interesting modifications?
> 
> - Aaron
> 
> P.S. That CA3083 - I remember Harry, I think, telling me to tell students 
> put the substrate pin the negative rail, or the transistors would act 
> weird - am I remembering that right
> 
> P.P.S. I love my job!
> 
> -----------------------------------------------------------------------------
> 
> Dr. Aaron Lanterman, Asst. Prof.
> and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
> College 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: Centergy 5212
> 
> 
> 
> 



	
	
		
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