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typical phaser lfo waveforms?

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daverdave:
Hey all, I was just wondering what the typical lfo waveform was used in most phasers. Is it triangle or sine?
I've been looking at building one up from scratch, I was going to have an lfo which was switchable between square and triangle, or square and sine. I know that a few I've seen use a triangle, like craig andertons EPFM phaser and the vermona 16 stage rack phaser. I wanted to know what the more common phasers use, like mxr's and small stones, cheers.
Dave

frequencycentral:
MXR's are triangle. The Ross is hyper-triangle, maybe the Small Stone is too? ROG's new Tri-Vibe has a very interesting LFO which does sine, triangle and hyper-triangle.

daverdave:
ah cheers mate, never heard of hyper triangle though, what's that?

frequencycentral:
Ross LFO with graphs: http://userdisk.webry.biglobe.ne.jp/000/024/65/1/200510_img_4.gif

The ROG Tri-Vibe, with some very useful LFO information and graphs: http://runoffgroove.com/tri-vibe.html

Mark Hammer:
Both the Ross and the Small Stone use "hypertriangular" LFO waveforms for slow sweeps, and something different for faster sweeps.  The "Color" switch on the Small Stone simultaneously selects between two LFO waveforms/outputs and two resonance settings.  The Ross opts for one sweep setting, but offers variable Resonance.  Below is the schematic of the first issue SS, which has the identical LFO "engine" that the Ross does, only with CA3094 chips and a few component value differences.

Both the Small Stone and the Ross have a 270k/100k divider going between V+ and V- (ground), providing a reference/bias voltage to pin 3 (with a .05uf smoothing cap).  [Osamu's drawing shows pin 14, but the Tonepad drawing will show pin 3; same function, just the other side of the dual chip.]  The SS has 280k of series resistance (100k+180k) from pin 5 to V+, and the Ross has 270k from pin 1 of its chip.  When you flick the Color switch on the SS, 100k of the 280k series resistance gets bumped over so that it is now in series with the 270k from pin 3.  In other words, the 270k/100k divider feeding pin 3 is now 370k/100k, while the 280k resistance between pin 5 and V+ is now 180k.  This changes both the overall range of sweep speeds, as well as the shape of the waveform. 

I've installed the functional equivalent of what you see on the Small Stone into a Ross phaser, and it works fine.  In principle, one can play with both the 270k/100k bias voltage and the 270k resistance on pin 1 (Ross) independently, so as to alter the speed range and waveform independently.  I haven't done it yet, but look forward to doing so.  I recall seeing some experiments that Osamu did, varying the 270k and achieving waveforms that were different in their degree of hypertriangularity.

Generally speaking, hypertriangular waveforms are optimal for slower resonant sweeps of both phasers and flangers, triangular a bit better for medium speed, and sine-wave optimal for vibrato.  One of the reasons why the old Boss CE-1 Chorus ensemble is so cherished is because it changes between triangle wave for chorus and sine-wave for vibrato setting.


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