[sdiy] Additive Synthesis questions

Stewart Pye stewpye at optusnet.com.au
Tue Jun 1 10:40:42 CEST 2010


Aaron Lanterman wrote:
> On Apr 11, 2010, at 3:04 AM, David G. Dixon wrote:
>
>   
>>> The Buchla 148 harmonic generator creates a fundamental triangle wave, and then goes through a bunch of contortions to shape that into the remaining 9 harmonics, in triangle form.
>>>       
>
>   
>> Aaron, do you have a schematic for this circuit, or even a description of how it actually works?  I can't seem to find anything definite on the web except vague descriptions of the module itself...
>>     
>
> Alas, as is usual with some of the rarer Buchla schematics, my source asked me not to distribute the original further. 
>
> I have a redrawn, simplified version of part of it that I did some analysis on (both pencil and paper and SPICE) that I may post somewhere someday...
>
> The basic idea is that he puts one of those diode bridges (like you see in the Yamaha GX-1 aka the MOTM-485, or the Korg-50 VCF and VCA) in the *feedback loop* of an op amp.
>
> - Aaron
>   

That sounds like it could be a deadband circuit. I can see how you could 
get doubling of frequency of a triangle wave if you mixed the output of 
the deadband circuit with the input. You could get variation in the 
waveshape by varying the input level but if you set it at a certain 
point you'd get a frequency doubled triangle wave. I could be way off 
here...

What I can't understand is how serge or Buchla got *3, *5 etc frequency. 
Could anyone shed some light on this?

Regards,
Stewart.





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