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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
CMOS phase shifting
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Taylor



Joined: Jul 13, 2006
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PostPosted: Sun Nov 14, 2010 6:47 pm    Post subject: CMOS phase shifting Reply with quote  Mark this post and the followings unread

I'm not a Lunetta guy, more of a stompbox user, but I "came up with" something kind of neat, which uses inverters to do phase shifting. Schematic is attached.

It's based on a logic building block from The Art of Electronics. An RC lowpass is used to delay the zero-crossing, and then this filtered signal goes to another inverter, and so on. Varying the resistance (here done by LED/LDR combo) changes the phase shift amount. The variable resistors too could be replaced with PWM'ed CMOS switches (4066) switching resistors above audio range.

I've breadboarded it and it does work. It's sounds like a phaser. Because I'm working with a guitar/bass signal, there's some extra wrapper circuitry for buffering, and an inverter used to square the signal, not necessary when you feed it a signal that's already square as in Lunettas. You could drop the first inverter for Lunetta use, meaning you can have a 5-stager with one inverter chip. Also in a Lunetta you already have an LFO so you can ignore the bit in the lower left corner.

Just thought this might be useful to somebody. More discussion is here.


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RF



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PostPosted: Sun Nov 14, 2010 8:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for sharing this Taylor - looks interesting...

bruce

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Draal



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PostPosted: Mon Nov 15, 2010 6:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks dude! Been looking for another phaser layout for my guitar so I'll definitely add your work to my To Do list Smile.
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Taylor



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PostPosted: Mon Nov 15, 2010 11:20 am    Post subject: Reply with quote  Mark this post and the followings unread

There are a couple of changes needed to build this from the schem:

-the values in the LFO (bottom left) make it an audio rate oscillator. You'll want to make the cap bigger and the 100k smaller.

-the first buffer is biased at 2.5v because the simulation software can only run the inverters at 5v. In a real build this point should be biased to half the supply voltage (4.5 in a 9v pedal).

You can play with a real-time simulation of this circuit here:

http://tinyurl.com/33dwhwh
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Taylor



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PostPosted: Mon Nov 15, 2010 11:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Taylor wrote:
There are a couple of changes needed to build this from the schem:

-the values in the LFO (bottom left) make it an audio rate oscillator. You'll want to make the cap bigger and the 100k smaller.

-the first buffer is biased at 2.5v because the simulation software can only run the inverters at 5v. In a real build this point should be biased to half the supply voltage (4.5 in a 9v pedal).

You can play with a real-time simulation of this circuit here:

http://tinyurl.com/33dwhwh


It's worth noting that if you play guitar into this, it will come out both fuzzy and phasey, because the inverters are used in digital mode (they square the signal up). I didn't mention this since Lunetta signals are usually squares to begin with, but I thought I should say something so you're not surprised if you build it.
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Draal



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PostPosted: Mon Nov 15, 2010 12:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the added tips. I'm a fuzz nut, (built a number of my faves and I know how key biasing is in those circuits Laughing ).

The added hair on this phaser should make things interesting. Tanx!

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loss1234



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PostPosted: Mon Nov 22, 2010 10:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

this looks cool

MAY I ASK..How did you make that CIRCUIT SIMULATOR?

thanks!

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Taylor



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PostPosted: Mon Nov 22, 2010 10:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Falstad.com
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Paradigm X



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PostPosted: Wed Feb 23, 2011 3:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Taylor

Firstly, thanks for posting this! I love phasers of all sorts so would love to build it.

But a couple of things;

THe link in your first post to further discussions is broken?

Secondly (im a bit of a noob so forgive any silly questions)

The green line after he first inverter is connected to nothing?
THe LFO Bottom left is used to set the rate correct? What size pot do you use?
My LDRs go up to 1Mohm - but surely the resistance depends on the brightness of the LEDs? Is there a way to compensate? Im thinking if i make a LDR/LED Combo, and vary the LED resistor, i can measure the LDRs resistance with a multimeter.
Can you explain a bit more about the cmos switching?

Sorry if this is all a bit ott. Ill try to breadboard a version up with the parts i have and see what happens.

Many thanks

BEn
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Taylor



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PostPosted: Wed Feb 23, 2011 3:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Ben. I guess DIYSB changed the link code or something, here's the original thread:

http://www.diystompboxes.com/smfforum/forums.html?topic=87949.0

The bit that appears unconnected is a switch. It's an SPDT switch; the unconnected part is the throw not currently connected.

The LFO doesn't set the rate, it creates the "swooshing" to begin with. A Phaser without an LFO doesn't swoosh around, it's like a static filter.

There's no CMOS switching in this circuit, really - the CMOS chip is used to do weird things to your audio signal.

I would be happy to answer more, but I would actually suggest you don't build this if you're a bit of a beginner. Some extra work needs to be done to get it working properly - it's not yet fleshed out enough to be "plug and play".

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Paradigm X



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PostPosted: Wed Feb 23, 2011 6:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi taylor

Many thanks for replying.

Of course, now youve said it its blatently obvious that thats the other side of the switch. Doh!

When i was referring to the cmos switching i meant the 4066 you referred to in your first post.

Out of itnerest, the sbdiy link still doesnt work.

But from what youre saying i should probaby wait.

Shame really, a fuzzy phase would sound awesome on 303 and i have all the bits lying around. I might spend an afternoon playing with them, you never know, might get something interesting.

many thanks

Ben
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Taylor



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PostPosted: Wed Feb 23, 2011 12:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't know why the link keeps not working. I'm posting it directly from a working page. But if you go to diystompboxes.com, click forum, then search, type in "cmos flange" it should be the top link, titled "CMOS Flange-chorus-fuzz. Would this work?"

Sorry, forgot about the 4066 switching. I was referring to the idea that you can use CMOS switches, switched by a PWM LFO at above-audio rate, to simulate varying resistors. See here for this concept. Again though, this would be somewhat advanced to implement so it wouldn't be easy, and you'd need to do some designing. You'd need a different LFO than the one in my schematic since it needs to be a PWM oscillator.

I do hope to revisit this idea when I get a chance. It's a cool idea and if I may be so immodest it's fairly original - quite unlike nearly all effect ideas since the 70s! If I do get it ironed out to be more buildable I will offer PCBs for it at my site. I have another circuit that's a pseudo-phaser, which should sound like a 12-stager but with only 6 stages to build. Titled "Bigger, crazier phaser with fewer parts". Again, I'd link it but for some reason the links won't work. But you should be able to plug that title into google and it'll be at the top.

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Paradigm X



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PostPosted: Wed Feb 23, 2011 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool man, thanks again.

Really weird about link, ive now signed up at SBDIY and can find it, exact same link and still doesnt work. Dont worry about it tho. (Im sure youre not Razz)

Cheers again for further info. Ill keep an eye on it.

I love all sorts of time based modulation so would be great. Ill check the other one two. Phase guru!

Cheers

Ben
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egasimus



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PostPosted: Thu Feb 24, 2011 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

The Phuzz Fase Laughing Must build, it sounds interesting Smile
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acidblue



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PostPosted: Thu Feb 24, 2011 12:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Forgive my ignorance but in the schematic are the chips an op-amp
and a 40106?
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