CMOS Flange-chorus-fuzz. Would this work?

[Taylor]

While curled up with ye olde Art of Electronics, I came across a circuit snippet used to delay pulse signals. It's an inverter, followed by an RC lowpass filter, followed by another inverter. Since the RC slows down the rising and falling edges, the time at which the signal crosses zero is delayed. The second inverter's output is therefore a delayed version of the original square/pulse signal

I simulated it and it seems to work as intended, but it can only delay a signal up to 90 degrees. So I wondered if it would be possible to use this to make a fuzzy flanger/chorus.

Another inverter is set up as an oscillator, flashing an LED which is coupled to an LDR used as the resistance element. Changing the resistance changes the rise/fall time of the square wave, and therefore the delay amount. In this configuration the oscillator will be a square, so not a good flange/chorus LFO, but I just didn't want to complicate the schem with filtering. I'm guessing that if you turned the speed up too high the signal would stop crossing zero and you'd get no sound.

No feedback is shown in this picture, but presumably if the idea works that part would be easy to add to get flanging sounds. As shown it should be a fuzzy chorus.

Is this basic idea worth messing with? Any fatal flaws escaping me? Would it work?

[slacker]

It will work, you'll get some sort of animated waveform out of it.
When delayed signal and the "dry" signal are high the output will be high, when they're both low it will be low and when they're different the output will be half the supply. So you get a stepped waveform, the width of the various parts will vary with the input frequency and the changing resistance.
Definitely worth chucking on the breadboard I reckon.

[Taylor]

I'll play around with it tonight I think. I'm thinking that it's probably more analogous to a phaser than a flanger, actually, as the time delay is not constant, but based on frequency.

If I use an opamp for the oscillator I can get 3 "stages" out of a hex inverter chip. Or, I don't know, perhaps I don't need 2 inverters per "stage", I'll see if I can just use one per after the first one. Maybe I'll make a CMOS Vibe pedal! 

[Taylor]

I simulated a 5-stage version (6 inverters). In this case I mixed all of the stages' outputs together, not just the final output with the clean. Here are the waveforms:



The square wave is the input signal. The second image shows the output with all the stages having a medium shift amount (1k resistor with 10u cap). The third image is the most shift possible, I think (5k with 10u).

You can see that it actually produces more than one peak per input cycle - 3 ups-and-downs at the output for every up-and-down at the input, which generates some "frequency tripling". So I think this thing will sound like a bit crusher/pulse width modulator/octave/phase type thing.  

I shall breadboard it tonight. Decided to save the inverters for shifting and use an opamp oscillator. I think I might be able to do this in 2 chips - a hex inverter and either a dual or quad opamp.

[frequencycentral]

Subscibed! 

[earthtonesaudio]

Subscibed! 

+1    And I one-up your smiley as well: 

[glops]

I can't wait to hear of your results, as well.

[caress]

nice looking waves!  pretty similar to sample rate reduction

[culturejam]

Subscibed! 

+1    And I one-up your smiley as well: 

+2

And here's an augmented smiley. 

[frequencycentral]

Subscibed! 

+1    And I one-up your smiley as well: 

+2

And here's an augmented smiley. 

No pressure though Taylor.....

[Slade]

Subscibed! 

+1    And I one-up your smiley as well: 

+2

And here's an augmented smiley. 

No pressure though Taylor.....

Who says noT?

+3!

[snap]

Escobedo didn`t mix his: http://www.diystompboxes.com/smfforum/index.php?topic=79822.msg659205#msg659205

[frequencycentral]

Subscibed! 

+1    And I one-up your smiley as well: 

+2

And here's an augmented smiley. 

No pressure though Taylor.....

Who says noT?

+3!

Yeah, you're correct. C'mon Taylor - deliver the goods! We are waiting impatiently.

[Taylor]

Escobedo didn`t mix his: http://www.diystompboxes.com/smfforum/index.php?topic=79822.msg659205#msg659205

I don't think what I have here is just PWM, even without mixing the outputs. If I just take the last output and mix it with clean, I get something like a variable crossover distortion, not simply a variable duty cycle square.

I do want to caution everybody that this might not sound much like a phaser or chorus or flanger. I'm not sure if the modulation aspect will be interesting or not, but even if it isn't, just as a very simple bit crusher with bit inversion should be kind of neat.

[caspercody]

Would love to hear a sound clip, when you get it breadboarded.

[Mugshot]

subscribed!

[Taylor]

Welp, I breadboarded it, but no luck. I had no sound at the first inverter's output, so I'm guessing my one and only inverter chip is dead (I did scrounge it from the junk bin).

If anyone wants to mess around with the idea, here's a more complete schem:

http://www.aronnelson.com/gallery/main.php/v/Taylor/cmos+flange3.JPG.html?g2_imageViewsIndex=1

A buffer would of course be needed on the end.

Also, if anyone wants to play around with the simulation, here's a direct link to the whole thing, just paste this into your browser and it will open up the app:

http://tinyurl.com/26y6xnf

[Earthscum]

Was just looking at that full schem... on the first inverter, try using a 100k-1M feedback resistor and let it self-bias instead of biasing it. It'll be running at full tilt. Your inverter may be good, not sure. I kinda remember having issues trying to bias inverters, and found the self-biasing to be more reliable.

[Taylor]

Was just looking at that full schem... on the first inverter, try using a 100k-1M feedback resistor and let it self-bias instead of biasing it. It'll be running at full tilt. Your inverter may be good, not sure. I kinda remember having issues trying to bias inverters, and found the self-biasing to be more reliable.

Well, whaddaya know? That did the trick. Playing with it some more now. Definitely some interesting stuff inside this...

Edit: right now I've only had time to do a very simple hardware build of this. Only 2 stages, and only one of them being swept with a manual pot. Even with just that, I can confirm that there is something kind of phasey going on here. So that's pretty exciting to me.

So the next step will be to make a real build with an LFO and some optocouplers sweeping the stages. I actually roasted a couple of NSL-32s earlier tonight, so I'll have to think about it in more detail. I think I was using a single current limiting resistor for the 2 optos - guess that was dumb.

[frequencycentral]

Soundclips? (no pressure, anytime today will be fine. Before lunchtime. In the UK)