PWM phaser in the works

[armdnrdy]

Welcome back Nelson!
Now get to work! 

[Mark Hammer]

Nice ideas Mark!

Why are there two 100nf caps I the feedback loop?  Isn't one sufficient?

Yes, I've actually been alittle confused about the purpose of the second cap myself. I took the feedback (more or less) out of another phaser that had two caps like that.
But as you say, one should be sufficient so I will remove the second one.

2) If you've going to use 3 chips, may as well make the third chip a quad, rather than dual, op-amp.  I know the 4066 only has 4 switches on it, but you can use the additional pair of op-amps for two fixed stages, as Rick Holt did for the Causality phaser.

I was going to make the third chip a quad anyway, but for other (less interesting) uses - one to buffer Vref (seem to reduce most of the LFO ticking bleeding into the signal)
and maybe that last op amp to buffer or beef up the LFO. Seems like it could be a good idea? But for the studio version I'll go all out and definitly add a couple of more passive stages aswell.
3. Great idea! I'll play around with a second LFO.
Thanks for the suggestions! 

The op-amp/JFET Ross Phaser uses an interesting approach wherein the feedback signal from the 4th stage passes through a fixed 5th stage back to stage 1 (instead of stage 2).  Essentially, it mimics the feedback path of a 6-stager, without having to resort to 6 stages.

[~arph]

Why not go all the way and add another quad and another 4066 and go eight stages. 

[Freppo]

It's a sign, I must start building stompboxes again.
Good luck with the phaser.

Thanks Nelson! Didn't expect you to visit the thread.
Yes, why not start building again?  It's a sign, for sure.

The op-amp/JFET Ross Phaser uses an interesting approach wherein the feedback signal from the 4th stage passes through a fixed 5th stage back to stage 1 (instead of stage 2).  Essentially, it mimics the feedback path of a 6-stager, without having to resort to 6 stages.

Yes, that a very cool trick and something I maybe wanted to add (as I wrote in my inital post).
Now I had one 1/4 of a quad opamp left, so it was perfect for that application.

Why not go all the way and add another quad and another 4066 and go eight stages. 

Yes, actually why not.  But I want to try to keep it a stompbox-friendly size for now.
Maybe in the rack-mounted "studio version"

[Mark Hammer]

The op-amp/JFET Ross Phaser uses an interesting approach wherein the feedback signal from the 4th stage passes through a fixed 5th stage back to stage 1 (instead of stage 2).  Essentially, it mimics the feedback path of a 6-stager, without having to resort to 6 stages.

Yes, that a very cool trick and something I maybe wanted to add (as I wrote in my inital post).
Now I had one 1/4 of a quad opamp left, so it was perfect for that application.

  Too distracted by the schematic to pay attention to the content of the post! 

[Freppo]

This is my progress and I dare say that it's just about finished.  
Maybe just a couple of tweaks here and there, but overall i'm very satisfied with the results.

I added a switchable second LFO that can make a odd wave-shape modulation together with first LFO.
And I added a switch to change the sweep (and tone of the phasing) though another inverter.


Full size: http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/parasit-phaser_final.pdf

Demo-video coming soonish, maybe sometime next week.
Now I have to study for a important test..  

/ Freppo

[Freppo]

The op-amp/JFET Ross Phaser uses an interesting approach wherein the feedback signal from the 4th stage passes through a fixed 5th stage back to stage 1 (instead of stage 2).  Essentially, it mimics the feedback path of a 6-stager, without having to resort to 6 stages.

Yes, that a very cool trick and something I maybe wanted to add (as I wrote in my inital post).
Now I had one 1/4 of a quad opamp left, so it was perfect for that application.

  Too distracted by the schematic to pay attention to the content of the post! 

Np Mark. I may actually have read about the ross phaser feedback in one of your old posts.. 
Keep sharing the knowledge and inspiration!

[Mark Hammer]

Incidentally, the 4n7 cap in the feedback loop of the feedback stage is a great idea.  I've noticed that higher feedback settings can often be accompanied by more cumulative hiss.  Some phasers will attempt to address it by using a treble-limiting cap in the feedback loop of the final phase-shift stage.  In some respects, it tackles the same problem the same way.  On the other hand, if you aren't using much feedback/regeneration you still forfeit top end.  While inserting treble-cut in the feedback path itself allows for full-bandwidth phasing when little or no feedback is applied.

[Kipper4]

Putting this on my to do list thanks Freppo.
Good luck with the test.

[deadastronaut]

any phaser than removes the need for matching 4 fets is cool in my book...

nice work freppo..

look forward to the vid demo..

[bloxstompboxes]

Putting this on my to do list thanks Freppo.
Good luck with the test.

Same here!

[anotherjim]

So, if you were to use (cough!) a PIC, AVR or one of the smaller Arduino's, you would use a PWM port without a filter straight to the CMOS switch inputs (given any necessary voltage level shift)?
In Arduino, I think this just means cyclically changing the variable in an Analog Write command. Maybe an easy way to get into some coding again. Hmmmm....

[Freppo]

So, if you were to use (cough!) a PIC, AVR or one of the smaller Arduino's, you would use a PWM port without a filter straight to the CMOS switch inputs (given any necessary voltage level shift)?
In Arduino, I think this just means cyclically changing the variable in an Analog Write command. Maybe an easy way to get into some coding again. Hmmmm....

Yes! That would probably work just fine.

[~arph]

Yes, but make sure to set the pwm mode to fast, or you'll hear it. And I think you either power and switch the 4066 from the same 5v supply or use four bits to do the level shifting. As I am not sure if the 4066 supply must be higher than the signal level swing

[GodSaveMetal]

any phaser than removes the need for matching 4 fets is cool in my book...

nice work freppo..

look forward to the vid demo..

Me too!!! and looking for your PCB yeahhhhh!!!!!!!!!!!!!!!!!!

[Freppo]

A little update..

I've built it up on PCB today that I designed during the small hours.
(I should be stuying but I'll do that later  )

It works, but I have a clicking sound now that goes tick tack, tick tack.. 
At faster rates it sounds like a frantic clatter, like a some kind of monster bug running on concrete
I don't have this problem on the breadboard.

Does anyone have an idea what could be the cause or how to solve it?

Here is the PCB for reference. http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/parasitephaserpcb.pdf
I don't recommend anyone building it until this issue is solved. Demo video will have to wait aswell. Frustrating!

/ Freppo

[Kipper4]

What happens if you disconnect the lfo? No Ticking?

[anotherjim]

Oooh, nasty when that happens.

Your layout looks sensible - LFO's all in one corner and wiring to pots & switches close by. Have you boxed it?

Try feeding the 40106 +ve supply pin 16 via a resistor before the filter caps. Say 270ohm?
If the pots have metal bodies, try fitting a ground wire to them - those can radiate quite badly if not screened.
Twist the wires to the LFO controls. Screened wire on ALL audio.

Last Vibrato I made had horrible ticking before boxing it (but didn't on the proto board). The foot-switch body was picking up off the LFO speed & depth pots - then injecting via stray capacitance to the switch contacts and into the high impedance (1M) input! Was fine once boxed.

[Freppo]

What happens if you disconnect the lfo? No Ticking?

Yes

I think the problem is using a quad IC. It's the only difference from the breadboard.
Now the LFO buffer/gainstage shares the same chip as the input and output stage..
I will have to try and confirm this on the breadboard, and most likely change the PCB layout into dual opamps.

Or maybe I'll go back to my original idea to have a dual opamp LFO, insted of using the CD40106 for this.

/ Freppo

[Freppo]

Oooh, nasty when that happens.

Your layout looks sensible - LFO's all in one corner and wiring to pots & switches close by. Have you boxed it?

Try feeding the 40106 +ve supply pin 16 via a resistor before the filter caps. Say 270ohm?
If the pots have metal bodies, try fitting a ground wire to them - those can radiate quite badly if not screened.
Twist the wires to the LFO controls. Screened wire on ALL audio.

Last Vibrato I made had horrible ticking before boxing it (but didn't on the proto board). The foot-switch body was picking up off the LFO speed & depth pots - then injecting via stray capacitance to the switch contacts and into the high impedance (1M) input! Was fine once boxed.

Thanks, I'll try with a resistor from pin 16 of the CD40106 to V+.
I'm have hooked up the PCB to a breadboard using small trimmers for pots

I'll report back
cheers / Freppo