Simple square-saw shaper?

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Blackened Justice
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Simple square-saw shaper?

Post by Blackened Justice » Wed Mar 17, 2010 3:08 pm

Hey, I'm about to build a MFOS WSG, and already have a number of mods planned. Is there any simple square-saw waveshaper I could consider implementing?

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gde
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Post by gde » Wed Mar 17, 2010 8:01 pm

unfortunately... square waves dont include any timing information; they are either up or down. a 0-5 volt sawtooth is easy to derive other waveforms from. if the voltage is at 2 volts, it is 2/5ths of the way through one cycle...
so you cant exactly convert a square to a saw

but if you look here
http://www.cgs.synth.net/modules/cgs21_ ... sycho.html
youll see the oscillators are also based off a 40106
if you grab the voltage at the input of the CMOS inverters and buffer them then you have a triangle(ish) wave for the oscillator
LOL

Blackened Justice
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Post by Blackened Justice » Fri Mar 19, 2010 6:04 pm

Yeah, I know about that triangle-ish wave, I'll and put triangle/square selectors for all three oscillators. So is it easier to turn a triangle into a saw than a square into a saw? If so, then could you please direct me to a simple tri-saw shaper?

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A Dingleberry Monstrosity
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Post by A Dingleberry Monstrosity » Fri Mar 19, 2010 6:47 pm

square waves dont include any timing information? WHat does that mean? :despair:
Clocks are square waves, beyond that I have no idea what "timing information" you could get from a triangle or sawtooth wave.


run it through some kind of integrator, done. Only issue is being able to get it to work perfectly for a range of frequencies and reset to zero after a cycle.
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Post by frijitz » Fri Mar 19, 2010 7:13 pm

A Dingleberry Monstrosity wrote:square waves dont include any timing information? WHat does that mean? :despair:
Clocks are square waves, beyond that I have no idea what "timing information" you could get from a triangle or sawtooth wave.
Hmmm ... the meaning seems pretty clear, really. After the square wave (or pulse, for that matter) signal goes high, you have no knowledge of when it is going to go back to low, since it is constant as a function of time. A wave with a ramp or other continuous variation changes with time, so if you know the amplitude you know the time. For example, when a ramp wave is at half of its peak value, it is also half way along its period.

You can put a square wave through an integrator, sure, but its amplitude varies as 1/frequency. You could level this with an AGC circuit, but there would be a time lag -- at least as long as the full period. Another way of saying that you need timing information that the square wave doesn't have.

:grin:

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Post by A Dingleberry Monstrosity » Fri Mar 19, 2010 7:40 pm

oh!!! OK!

now Im on the trolley, thanks for explaining!
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Post by Blackened Justice » Sat Mar 20, 2010 5:48 pm

Thank you for the insight on why it would be quite difficult to implement ;)

Now, I have some other questions:
1) Why does the oscillator circuit use inverting Schmitt triggers instead of inverting comparators? Wouldn't the use of comparators make it much easier to implement PWM?

2) Would sync be possible if I do it like it's done in this circuit: http://www.electro-music.com/forum/topic-23878.html ?

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Post by Blackened Justice » Mon Mar 22, 2010 6:30 pm

Image
Couldn't I use this circuit? Is this how they did it in the vintage divide-down string-machines? My interest is not generating a clean saw, just getting some even harmonics in the machine ;)

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Re: Simple square-saw shaper?

Post by mager » Sun Aug 30, 2020 12:06 pm

Did anyone try this circuit?
I've put it into the simulator and it does not seem right (only at 600 Hz)

http://www.falstad.com/circuit/circuitj ... twDfb8PyAA

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htor
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Re: Simple square-saw shaper?

Post by htor » Tue Sep 01, 2020 1:58 am

have you tried generating a sawtooth directly with the 40106 and buffering that with an op amp? just put a diode in parallel with the feedback resistor (pointing to the cap) and you should get one.

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Re: Simple square-saw shaper?

Post by Rex Coil 7 » Tue Sep 01, 2020 2:58 am

htor wrote:
Tue Sep 01, 2020 1:58 am
have you tried generating a sawtooth directly with the 40106 and buffering that with an op amp? just put a diode in parallel with the feedback resistor (pointing to the cap) and you should get one.
So the half wave rectification of the square wave results in a sawtooth?

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htor
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Re: Simple square-saw shaper?

Post by htor » Tue Sep 01, 2020 3:58 am

Rex Coil 7 wrote:
Tue Sep 01, 2020 2:58 am
htor wrote:
Tue Sep 01, 2020 1:58 am
have you tried generating a sawtooth directly with the 40106 and buffering that with an op amp? just put a diode in parallel with the feedback resistor (pointing to the cap) and you should get one.
So the half wave rectification of the square wave results in a sawtooth?

<incomprehensible>
lol,

you take the voltage at the inverter input (normally a triangle), not the inverter output. i got the tip from this article, near the bottom:
https://hackaday.com/2015/03/09/logic-n ... waveforms/

Screen Shot 2020-09-01 at 10.58.04.png
it's not a perfect sawtooth, but something almost like it.
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Re:

Post by jorg » Tue Sep 01, 2020 10:46 am

Blackened Justice wrote:
Fri Mar 19, 2010 6:04 pm
Yeah, I know about that triangle-ish wave, I'll and put triangle/square selectors for all three oscillators. So is it easier to turn a triangle into a saw than a square into a saw? If so, then could you please direct me to a simple tri-saw shaper?
If you have both the square and the triangle (normally that's the case if you build any triangle-core VCO), it's simple to convert them to saw. Use the square to drive a switch that inverts the polarity of the triangle.

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Re:

Post by jorg » Tue Sep 01, 2020 10:49 am

A Dingleberry Monstrosity wrote:
Fri Mar 19, 2010 6:47 pm
square waves dont include any timing information? WHat does that mean? ...
run it through some kind of integrator, done. Only issue is being able to get it to work perfectly for a range of frequencies and reset to zero after a cycle.
They don't contain slope information. "Some kind of integrator" needs to know what slope to run at, which would imply knowledge of the CV.

However, analog VCOs almost always have a triangle or saw in the core, so the slope actually is available.

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Re:

Post by jorg » Tue Sep 01, 2020 10:52 am

Blackened Justice wrote:
Mon Mar 22, 2010 6:30 pm
Image
Couldn't I use this circuit? Is this how they did it in the vintage divide-down string-machines? My interest is not generating a clean saw, just getting some even harmonics in the machine ;)
This will only work accurately at one pitch; maybe crudely for an octave. The saw slope is fixed, meaning the amplitude will vary with frequency, and/or there will be gaps, resulting in a sharktooth waveform.

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Re: Re:

Post by jorg » Tue Sep 01, 2020 10:58 am

jorg wrote:
Tue Sep 01, 2020 10:46 am
Blackened Justice wrote:
Fri Mar 19, 2010 6:04 pm
Yeah, I know about that triangle-ish wave, I'll and put triangle/square selectors for all three oscillators. So is it easier to turn a triangle into a saw than a square into a saw? If so, then could you please direct me to a simple tri-saw shaper?
If you have both the square and the triangle (normally that's the case if you build any triangle-core VCO), it's simple to convert them to saw. Use the square to drive a switch that inverts the polarity of the triangle.
SawShaper.PNG
Square goes to the control input of the switch; triangle goes to the common terminal of the switch.
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