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

[tuckster]

keto: it looks good!

I'm going to solder the LEDs to the 3PDT because I always think the phaser is on just because of the aditional LEDs that are always on.

[Mark Hammer]

Up to my armpits in phasers, so I hadn't bothered to check in on this thread in a long time.  It was a lazy Saturday so I figured I'd etch me a couple of boards.  One of the spare pieces of copper board accommodated a pair of Causality4 MkII boards perfectly, so I figured what the heck, etch 'em.  Next obvious step was to check in here and see if there were any changes, samples, suggestions, mods.

Having listened to the samples submitted, and Keto's excellent video demo (cute graphics), this baby has moved way up the list.  The additional controls make this a really fun little toy. 

On top of a vibrato (dry-lift) switch, and wet level, one of the things I'm pondering is adding a little daughterboard with 2 extra fixed stages (one lag, and one lead), a unity-gain inverting stage, and mixer/output stage.  The intent is to provide a sum and difference output for stereo, but use the additional stages to stagger where the phase-shift maxima is/are so that the sum and difference outputs don't cancel out in air.  Normally, if you have matched sum and difference outputs, and feed them to separate amps, the effect effectively cancels out acoustically.  The intent here is to make it a more robust "stereo" by making the sum and difference a little more dissimilar.

I was pondering a phasefilter switch, but thought better of it when I realized that it required using up the two swept stages, leaving only two fixed stages.  I suppose if someone wanted to make a modulated lowpass filter, and skip the swept notch, it would be worth doing; particularly when one considers what the variable shape and range controls permit in the way of sonic options.  We`ll see.  I have some chassis with holes drilled in them already for other projects.  If a spare hole persuades me, I`ll do it.

For now, thanks to Rick for doing this, and thanks to the others for their ideas, and persuasive soundclips.

[keto]

I had asked elsewhere about how to add a wet mix knob, but not had a reply.  It's definitely still over my head.  It could stand to be a touch wetter for use with distortion.  The vid I did over emphasizes the phase sound, relative to what I hear in the room.  It's a while since I did that, but I think I was estimating around 60% wet as-is, and my desire to have the ability to take it as high as possible.

[frequencycentral]

I recently reduced the value of R7 to 1k in mine. Increasing the timing cap C4 to 47uF got me really slow speeds but at the expense of faster speeds, reducing R7 sorts this out nicely.

R13 and R14 mix the wet and dry signal, reducing R14 or increasing R13 should give a wetter mix.

Now Mr Hammer is onboard expect major revisions...................

[Mark Hammer]

As noted, the ratio of R13 and R14 sets the dry/wet balance.

Personally, I have never really found a use for mixes that were more wet than dry, so I tend to stick with a complete dry lift (via toggle), and variable wet mix, rather than a wet/dry balance pot.  YMMV.

That being said, the balance of wet and dry to achieve maximum cancellation is a function of the actual amplitudes of each at the mixing node, NOT the numbers on the schematic.  All these parts have tolerances, remember.  So, it pays to have the capacity to zero in on maximum cancellation by including a theoretical too-much-wet setting.

So, being able to adjust wet level for subtlety AND optimum cancellation, might incorporate replacing a 27k mixing resistor with a 22k resistor and 100k pot wired as variable resistor.  This will let you go from more wet than dry (which may well be flawless 50/50 mix in actuality, given tolerances), to around an 80/20 (dry/wet) mix for just a touch of animation in the background.  Worst case scenario is that with the wet dialed up full, putting it into vibrato mode (dry cancellation) results is a little bit of boost.

Finally, for the adventurous, there is always the option to use envelope control of speed.  Simplest thing is to use the output of the op-amp input buffer stage to feed something like a Dr Q/Quack rectifier, and use that to drive an optoisolator, with the LDR placed in parallel with the speed pot.  Play harder, or turn the envelope sensitivity up, and the speed increases as you dig in.  Naturally, with the LDR placed in parallel with the stock 470k speed control, turning the speed up manually would imply less impact of the LDR.

[Mark Hammer]

Okay!  Finally finished wiring and firing it up, and this is a neat little gadget.  I built mine with an LM324 and LM1458 for the quad and dual op-amps, simply because they were handy, and used a 50k Regen pot (instead of 10k) to be able to dial in more shimmery sounds.  Works just fine. 

Didn't fire up properly at first because I failed to pay proper attention to ALL the cues for chip orientation, and was misdirected by the U1 and U2 legend being the same orientation in the picture (and no notch indication!).  It may well have been brought to our attention in this thread, but at damn near 240 posts, I wasn't about to read them all, and simply worked from the drawings alone.  Measuring what I thought was V+, and I got readings below 1Vdc with a fresh battery, so I took a look at the datasheet for the 324 and realized I had installed the chip the wrong way around.  Desoldered and resoldered it back in properly, and it fired up right away.  Watch out for those square pads, kids!!

The Range control is almost worth putting in a foot-pedal.  I find that setting the speed and Shape just right, one can play with the Range pot and get quasi S&H filter sounds.  I look forward to dickering with the allpass/lowpass thing and seeing if that provides a more pronounced S&H sound.  The first one, though, will remain plain vanilla, with the exception of an always-direct out jack and a switch for selecting pure wet, a 66/33 mix of dry/wet, and a 50/50 mix for the main output jack.  That'll let me run it in "stereo", without having to implement any fancy sort of bypass switching.  With the 2nd jack always clean, bypass only has to be implemented for the effect output.  The next build after that will have some other frills, like an additional 2 stages, sum/difference, and envelope control of the speed.

The usability of the Shape control is partly a function of the Range and Width controls.  That is, extreme Shape settings (ramp or sawtooth) tend to produce undesirable thumps when the Range is set too low and the Width is too strong.

At max Regen, I'm getting oscillation, so I think I'll either a) put a 470R resistor in series with the pot, b) replace the 10k fixed resistor with an 11k, or c) measure the existing resistor and see if I can find one that is at the higher end of the 5% tolerance.  One of those oughta work.

Again, many thanks to Mr. Central for this.  Now that I managed to score a pair of 4526 chips to complete my E&MM Harmony Generator, I'm looking forward to some interesting sounds this autumn.

[Mark Hammer]

We have a government-wide United Way charity drive every autumn, and in past I've contributed pedals to a silent auction to raise money.  A chorus pedal last year raised $100.  I think this year's will be the Causality IV.

[frequencycentral]

That's great Mark. So can we look forward to some Hammer mods? 

[tubelectron]

Hi frequencycentral,

I'm thrilling waiting for mine. I'll post pics and and comments (if you don't).

A+!

[pantufla]

Here's the artwork for the 5 knob MkII PCB, it includes pads for the addition of an extra stages daughter board - more on this some other time! The 3 knob MkI version can also be built using this layout.

how big is this Board?

[Mark Hammer]

It fits nicely into a 125-C type box.  Maybe someone else can chime in about 1590B style.

[Labaris]

Each "step" (the minimum distance between two terminals) should be about 1/10 inch (2,54mm).
So you can count them and do the math to see how big is the board

[frequencycentral]

Another C4 MkII. I built this one for tubelectron. It features a new layout with a few value tweaks and provision for a trimmer to set the output level, PCB from guitarpcb.com and waxing/waning LEDs situated in the hull of NCC-1701.

[Steve Mavronis]

Cool how you have the LED's arranged as portholes of the Enterprise-A, etc.  

[Govmnt_Lacky]

Some defined values for the pots would be nice. Speed, Shape, Range, Width, and Regeneration.

Look killer. Might be my next endeavor. Thanks again Rick. 

[tubelectron]

Hi Rick,

Now I am in my garden waiting for your UFO's Causality 4 MkII phaser arrival... By night, of course... I won't be mistaken, I think...

A question : there is no battery clip installed inside = it would draw too much current from a 9VDC batt ?

A+!

[frequencycentral]

Ok cool! So Mark Hammer has implemented extra stages to his Causality:  http://www.diystompboxes.com/smfforum/index.php?topic=87166.msg733708#msg733708

Once again, I find myself without a Causality, having sold my MkII, and built another MkII for Bruno. So it'll soon be time for me to build another for myself. Several possibilities present themselves with my next build (I might as well try something different!):

• Extra stages, ie a second LM13700 implemented as Mark did his.
• A seperate Range pot for the extra stages - two sets of notches, one 'bright', the other 'dark'. Or.....
• Extra (modulated) stages with a seperate Range pot using the 'wet only' pads as send and return, or in parallel with the existing modulated stages. The intention being to achieve parallel phasing with two sets of notches, one 'bright', the other 'dark'.
• Some additional (switched) fixed stages using the 'wet only' pads as send and return. The fixed stages having four different cap values. The intention being an attempt at through-zero-phasing by delaying the dry signal with respect to the wet (modulated) signal.

All highly speculative I know, but I'm gonna try it all. The more I think on it, the less likely it is that I'll build a stock PCB and try some mods. I'll breadboard the whole thing again and try everything, probabaly do a new layout incorporating whatever works well. Any other ideas I should try? This may be a couple of months away......

[Morocotopo]

Rick, I´ve been following this thread, will build one eventually.
Regarding new features, I always thought that the usual triangle / whatever wave for modulating was quite boring, so, why not make a more interesting LFO? Sequenced a la seek wah, two parallell LFO´s, another LFO modulating the main LFO, envelope controlled LFO speed or depth, etc etc... just my personal ideas.

Great work!

[tubelectron]

Rick, I´ve been following this thread, will build one eventually.
Regarding new features, I always thought that the usual triangle / whatever wave for modulating was quite boring, so, why not make a more interesting LFO? Sequenced a la seek wah, two parallell LFO´s, another LFO modulating the main LFO, envelope controlled LFO speed or depth, etc etc... just my personal ideas.

Great work!

Hi Morocotopo,

Your idea is good - I have tried one which is probably similar in the sounding result : 2 phasers paralleled with different rates. I discovered that it was the way was obtained the miraculous viola/violin tones on my old Crumar Multiman I , and certainly on Elkas too.

A+!

[frequencycentral]