Saw (was: square) wave FUZZ box ?

[Paul Perry (Frostwave)]

Given a genuine square wave (not easy, if you are starting from a guitar) it should be simple to make a saw, just by turning on an integrator when the square wave goes positive, and discharging it quickly & starting over on the next positive edge.

If you discharge it when the square goes negative then you don't end up with a saw tooth - you get tooth, space, tooth, space etc.  You need two integrators - one of which is switched from an inversion of the square so you get space, tooth, space etc - along the lines of what I did above, then both sides get 'zipped' together with a mixer. 

Some confusion here, I didn't mean to integrate the square wave. I just meant to start a ramp, on each uptick of the square wave. And yes, in practice the square wave will be raggy, with awful consequences.

[gez]

guys you scare me

Is it because we're bearing our (saw) teeth?! 

[gez]

Some confusion here, I didn't mean to integrate the square wave. I just meant to start a ramp, on each uptick of the square wave.

Don't worry Paul, no confusion, I understood you.  The circuit I posted does exactly what you say (input signal controls switches which allow passive integrators to charge and discharge)

[H S]

Didn't realize you were already there, Gez!

This is starting to sound like something you could do with a "Crash Sync."  Like, if you make a low frequency saw and sync it to restart at every uptick of a guitar input.

I think you can get something in the neighborhood of a saw with an E-H µsynth.  A saw has every overtone in the harmonic series, falling off in amplitude as 1/n.  A square is the same, except that it only has the odd harmonics.  The "octave up" slider on the µsynth should fill in some of the even harmonics, so combining the "square" and "octave up" sliders should get something saw-like.

(Cool--I just went to look at mine, and I had left it set: sub-octave 0, guitar 0, octave up 5, square 3.)

[GFR]

This page's about Roland's GR300:

http://www.joness.com/gr300/patent.htm

Basically they do like Paul Perry suggested: get a square wave (a good one, since they use a hex pickup, adaptive low pass filtering, zero crossing, etc.) and use the up edge of the square wave to reset a ramp generator. The amplitude will be of course bigger for lower notes (since you have a hex pickup it doesn't need to cover the full guitar range but it's still ~ two octaves) so they add a diode clipper, and the final wave is a saw with a frequency dependant degree of clipping. Add envelope control and a four pole VCF and call it a synth, like Tim said

[GFR]

BTW, puretube, for your collection:  Patent Number: 4,357,852

[gez]

The amplitude problem RG mentioned was got round by using passive integrators.  With lower frequencies the waveform gets compressed due to the longer time constants. 

I had a feeling I'd typed up something wrongly.  That should have read "gets compressed due to the 'short' time constants of the integrators".  In other words, at the highest frequencies the caps ramp up close to full voltage within half a cycle, meaning at lower frequencies the waveform ends up getting compressed/distorted.  Sorry about the confusion (if there was any)...perhaps I've made it worse?

[A.S.P.]

add...and call it a synth, like Tim said

no problem - has been done before - but this thread was asking about Fuzz Boxes...

[GFR]

OK. Inspired by Joe's Shocktave:

• It's not a linear ramp, it's an exponential ramp.


• The amplitude is roughly the same for the entire frequency range.


• Invert the polarities for rising or falling ramps.


• There's a DC level (proportional to the frequency).


• Untested.

Thanks to ImageShack for Free Image Hosting

[markphaser]

Where is the schematic for a Korg PME Wave shaper i can't find it?

What other wave shaper guitar pedal is there?

What is wave folding?

[TELEFUNKON]

these are nice:

Bloe-Joe-7

Bloe-Joe-6

[gez]

From the waveforms, I'd say that no comparator based squaring was done, just heavy clipping then shaping.  Even if that's not the case, that's something I'm going to have to try as it's probably a lot more musical than the comparator circuits (no splutter).

Thanks for the link Mr Funk, interesting experiments! 

[Sir H C]

If you did slew rate limiting you could approximate a sawtooth.

[puretube]

This TUBE-SAW would rather be in a/the "Tubes as Diodes" - thread, but...

[Processaurus]

Those waves resemble Roland's early GR300, a sawtooth with the top chopped off.

Their 80's analog solution to changing guitar to sawtooth:
http://www.joness.com/gr300/patent.htm