New Phaser Design - “Causality 4” – Built with you in mind!

[frequencycentral]

The go-to phaser builds for DIY’ers are:

Phase 45 – Intermediate build. 2 stages. FET matching required. No regen. Very subtle.
Phase 90 – Advanced build. 4 stages. FET matching required.
Ross Ropez – Advanced build. 4 stages. OTA design.
Small Stone – Advanced build. 4 stages. OTA design.

The design concept for “Causality 4” was to achieve a musically useful intermediate build 4 stage phaser with regen, using easily available parts, and requiring no matching of components. It has two swept stages using a dual OTA, and two fixed stages using opamps. The LFO utilises a dual opamp and is based on the MXR phasers, much simpler than the LFOs in either the Small Stone or Ross Ropez. The fixed stages came from an idea suggested by Mark Hammer in this thread: http://www.diystompboxes.com/smfforum/index.php?topic=80111.0 Having four stages, even if two are fixed, allows for the addition of regen, which for me is a phaser essential. The Regen control goes from zero to just short of self oscillation - some great sounds available here. The Depth control is particularly interesting and useful, specifying where in the spectrum the phasing occurs.

Your critiques are welcome!

Soundclips, perf and PCB layouts to follow - it's on the breadboard ATM, I want to build it first.

[guitarman89]

great work! I wish you will post sample soon! It's so interesting to me, I love phaser...

[Stompin Tom]

Looking pretty cool. I'm keeping my eye on this thread...

[daverdave]

Looks really good mate, I was looking at Mark's post the other day, fixed stages sounds very interesting. I'll be very interested to hear some sound samples.

[jacobyjd]

Excellent. Thanks for putting the time into this, Rick. I think I just found my phaser.

[sean k]

Even before the first post I got it down and then this morning started designing up a PCB, my favourite part and it's really quite an elegant set of traces. With the opamps hanging off each end of the OTA it makes sense to have the quad opamp below the Ota and amps A and D as those on either end. It gets rather confusing for the VR feeds but a little complication always makes the PCB design process interesting. Thanks for the challenge Rick 

[StephenGiles]

Looks interesting, can you please explain how the output mixer/amp is configured - gain etc?

[Thomeeque]

 Those 33nF capacitors attached directly between two outputs look bit weird to me

 Output buffer mixing 3.5*dry - 2.5*wet as well (there is maybe "typo", is not? That 47k resistor connected this way makes no sense there imo)

 But you say it works, so..

 Please give us samples asap Thanks, T.

[frequencycentral]

Even before the first post I got it down and then this morning started designing up a PCB, my favourite part and it's really quite an elegant set of traces. With the opamps hanging off each end of the OTA it makes sense to have the quad opamp below the Ota and amps A and D as those on either end. It gets rather confusing for the VR feeds but a little complication always makes the PCB design process interesting. Thanks for the challenge Rick 

I'm starting to think that using two duals instead of the quad will make for a neater, more compact layout.

Looks interesting, can you please explain how the output mixer/amp is configured - gain etc?

Output buffer mixing 3.5*dry - 2.5*wet as well (there is maybe "typo", is not? That 47k resistor connected this way makes no sense there imo)

I screwed up on the schematic drawing the output stage,  I've re-uploaded it now, refresh your browser to see the revision. Does that look better? I originally tried to output/mixing stage of the Ross, but I was getting slightly less than unity, so I reconfigured it to what it is now, which gives unity at the output. Sorry for the error guys,   

Those 33nF capacitors attached directly between two outputs look bit weird to me

This design takes a little from the Ross, a little from the Phase 90, and a little from me.  The two OTA stages are identical to those in the Ross though: http://www.tonepad.com/getFile.asp?id=99

I've also added a 10K resistor between lug 1 of the Depth pot and ground, as I found weird things were happening with the pot fully grounded. It doesn't do much to limit the range, but sorts out the issue.

[Thomeeque]

Those 33nF capacitors attached directly between two outputs look bit weird to me

This design takes a little from the Ross, a little from the Phase 90, and a little from me.  The two OTA stages are identical to those in the Ross though: http://www.tonepad.com/getFile.asp?id=99

 Oh, I see!

[frequencycentral]

Oh, I see!

Don't be bashful! And thanks to you and Stephen for alerting me to the error in my drawing of the output stage.

[StephenGiles]

Ah, that makes more sense now, many thanks. For a fatter sound, perhaps a second phasing network in parallel with the first but using different capacitors.

[Thomeeque]

Oh, I see!

Don't be bashful! And thanks to you and Stephen for alerting me to the error in my drawing of the output stage.

 To be honest, I've made one error in that second statement either - dry signal ratio would be different (I've forgot to calculate-in influence of that 47k resistor)

 T.

[frequencycentral]

....................and sorry Scruffie I won't be doing a vero layout! 

[culturejam]

Ah yes, you finished your sooner than me. And it probably sounds better. 

Backgound:
http://circuitworkshop.com/forum/index.php?topic=174.0

My dual OTAs are in and I'll start working on OTA version over the long holiday weekend.

[frequencycentral]

Ah yes, you finished your sooner than me. And it probably sounds better.  

Ah yes CJ, but if you hadn't asked this question around the same time as Mark Hammer posted this thread I never would have done this design. So props to you both.  

[Scruffie]

....................and sorry Scruffie I won't be doing a vero layout! 

I actually thought about asking... but I thought seeing as how much you love it you'd be doing it anyway.

[Ben N]

Looks great, Rick. I can barely find the time to build a booster, I don't know how you manage to be so productive.

[frequencycentral]

Looks great, Rick. I can barely find the time to build a booster, I don't know how you manage to be so productive.

Well, y'know, at the expense of everything else, life, work, relationships, family...............

Anyway, here's a soundclip for ya: http://dl.dropbox.com/u/967492/Causality%204%20Phaser.mp3

Signal Path:

My below average guitar fumblings  >>>  Squier Tele Custom (bridge humbucker)  >>>  Big Muff Violet Rams Head (clone)  >>>  Causality 4 (on the breadboard)  >>>  Harley Benton GA5 (VJ clone)  >>>  Shure SM58  >>>  Wavelab.

No other processing. A montage of different settings, a bit of extreme knob twiddling going on too.

[frequencycentral]

.....and here's a clean clip: http://dl.dropbox.com/u/967492/Causality%20Clean.mp3

Signal Path:

My below average guitar fumblings  >>>  Squier Tele Custom (bridge humbucker)  >>>  Magnus Modulus (a bit of chorus and delay)  >>>  Causality 4 (on the breadboard)  >>>  Harley Benton GA5 (VJ clone)  >>>  Shure SM58  >>>  Wavelab.