[sdiy] Triangle wave octave generation (frequency doubling)

HOSHUYAMA houshu at muj.biglobe.ne.jp
Thu May 28 15:14:51 CEST 2009

Hello Tom,

Alisa 1377 and 1387 use fullwave rectifiers.



Sam Hoshuyama
Saitama, JAPAN

Tom Wiltshire wrote:
> Hi all,
> Once upon time, long, long ago, I built a little circuit which  
> consisted of a triangle wave oscillator followed by a series of  
> precision fullwave rectifiers (the op-amp based variety). The  
> rectifiers folded the bottom half of the triangle wave up and thereby  
> doubled the frequency. With a bit of trimming, I was able to get  
> about 4 octaves above my input triangle wave out of this before the  
> waveform quality began to suffer.
> Looking at those SH2000 schematics this morning reminded me of this  
> early experiment with frequency dividers/doublers.
> Does anyone know any synth/organs that have used this triangle- 
> folding trick? I've often wondered why more organs didn't use it,  
> since they often filter the square waves from flip-flop dividers to  
> try and get sine waves - you'd get a better result if you started out  
> with less harmonics to begin with.
> Thanks,
> Tom
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