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Module #4 - Magnus Danielson sawtooth phase shifter
January 31st, 2011I keep postponing writing the build log of these modules, but here’s the 4th module in my rack, a Magnus Danielson design sawtooth phase shifter which is really an extension of the sawtooth octave doubler design on the same page. Magnus created these schematics 10 years ago to be as simple as possible, and this particular one contains an error which you should fix if you want to build this module. You’ll have to figure out for yourself, though…
I also broke out the internal comparator, which could be used to make a PWM easily.
As always, here’s a video of me playing around with the module, with an oscilloscope so you can see the waveform. Please turn on 720p for slightly better audio quality. (Should already be on by default in this embedded player.) There’s a bunch of annotations throughout the video explaining what I’m doing.
The next module I’m planning to build… Will probably be a cool one, so stay tuned.
January 11th, 2012 at 11:55 pm
Ah, so that’s how it eventually worked when built in reality… a “sawtooth plus PWM-pulsewave” instead of a sawtooth phase shifter?
January 12th, 2012 at 12:06 am
Yeah, that’s what the implementation of it ends up being. The sawtooth is a separate module (this is a modular synth mind you.) Having a sawtooth counteract the wave at certain places just happens to do what we want. But if you feed it a sine like I did at a later point in the video, it becomes very obvious that what you’re looking at is a PWM generator controlled by and added to the original signal.
May 18th, 2012 at 5:05 am
So… ok, I suck. Whats the error in the schematic? Please?
May 18th, 2012 at 6:45 am
Oh, I thought I had mentioned it somewhere. The + and - inputs are swapped on the first opamp.