[sdiy] Triangle wave octave generation (frequency doubling)

Aaron Lanterman lanterma at ece.gatech.edu
Wed May 27 18:43:08 CEST 2009

On May 27, 2009, at 11:12 AM, Steve Ridley wrote:

> The Buchla 148 took this trick a bit further.

Wild coincidence - I just got to play with a Buchla 148 system this  
weekend while I was visiting New York, courtesy Reed Hays, a really  
nice guy who happens to have the largest Buchla system I think I've  
ever seen (not that I've seen many in person, but counting the ones  
I've seen in photographs).

I patched all the harmonic outputs of the 148 into LPGs set in gate  
mode, and then drove each gate with a different envelope for some  
crude additive synthesis.

The "sine" waves coming out of the 148 were far from pure, which I  
thought made the unit more interesting.

 From what I've gleaned from various postings, the 148 has a triangle  
core, gets the odd harmonics using wavefolding circuitry like in the  
259 or the Music Easel, and uses rectification and shifting to get the  
various even multiples of those odd harmonics. (I think it was a post  
by Mark Verbos that confirmed this, but I can't recall for sure now.)

I'd really be interested to see exactly what's inside that box.

The Easel and 259 wavefolder circuits are based on adding the results  
of a set of deadband circuits made by "voltage starving" op amps (I  
haven't seen this anywhere else). All the 100 series schematics I've  
seen use discrete transistors, so it would be interesting to see what  
he did.

- Aaron

P.S. I also got to meet up with Charles Cohen (he even let me play  
with his Music Easel, and he let me commit blasphemy on his 200 system  
by letting me try to set up a Moog-style four-pole-with-feedback  
patch) and Dan Snazelle from this list. Dan and I had a fantastic  
lengthy chat over all things SDIY over coffee in Greenwich Village.

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