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

[deathfaces]

A guy on another forum asked about adding extra swept stages. "Causality 6", unverified.

Sexy just got sexier!

[frequencycentral]

......or there's always the option of sandwiching this in between the two swept stages of Causality 4

[sundgist]

A guy on another forum asked about adding extra swept stages. "Causality 6", unverified.

Now I'm really looking forward to getting this built.
I reckon I can get extra stages added on a seperate board with just a trace cut and some wiring to my vero.
Cut trace at i11 and insert the extra stages between the 13700's two opamps, then just supply the new board with 9V, Vref, GND and Depth from a1.

Switch to select no. of stages might be on the cards...!

I'll draw this up and post once i build what i've got so far.

"I'm gonna need a bigger box"

[frequencycentral]

Important Update:

I've been experimenting to get a wider LFO sweep. I played around with the LFO on the breadboard and found that if I replace R5 with a 47k resistor (was previously 220K) I get a broader LFO sweep, which is very pleasing.

For anyone who has already built this and wants to apply the 'wider LFO sweep mod' without removing R5 from the board, just parallel it with a 68k resistor, which will give you 51k.

The mod also has the effect of slowing down the LFO, so the fastest speed is slower, but so is the slowest speed.

It also has the effect of making the LFO sweep slightly asymetrical. Subbing a 68K for R5 gives a deeper sweep ,though not as deep as a 47K, but the symetry is better. If you want to do this without removing R5, parallel it with a 100K.

[Ripthorn]

I think I would just stick a little switch in there to choose between the two.  Now I'm just waiting for you to do this with submini tubes...

[jkokura]

So where do you find the IC's? I just checked at Small Bear's site, but couldn't find the LM13700 or the TL084. Perhaps Mouser or such, but I'm trying to find them and since I've only ordered from Smallbear and PPP I'm not sure how to track those parts done.

jacob

[Ripthorn]

Mouser or Digikey should carry those.  The LM13700 is (if I remember right) a dual or quad OTA and the TL084 is a type of quad opamp.  They are just not your typical TL072 or similar that Small Bear carries.

[Lurco]

13600/-700 are dual: http://www.smallbearelec.com/Detail.bok?no=224  http://www.smallbearelec.com/Detail.bok?no=789

[mafew129]

I just built the C4 on vero. When the pedal is turned on i am getting a significant drop in volume. Also the regen knob does not seem to work at all. Has anyone built this on vero and got it to work? I know its not verified.

[frequencycentral]

I just built the C4 on vero. When the pedal is turned on i am getting a significant drop in volume. Also the regen knob does not seem to work at all. Has anyone built this on vero and got it to work? I know its not verified.

I haven't fully checked that stripboard layout - I actually avoid stripboard like the plague and have a real problem 'reading' stripboard layouts. But:

- The 6k8 resistor between r13 and s13 should be 68k, that will explain the volume drop.

- On reflection, the regen pot should probably be a lower value than 47k, probably 10k or 22k would do. Try maxing it out - it should start to howl, if it doesn't there must be some other issue either with your build or with that layout. The 10k resistor between n2 and n4 stops the device from self oscillating, you could try a lower value there, but I found that even dropping it to 8k2 caused self oscillation with the regan pot maxed.

Did you use LM13700 and TL084 as specified? A guy over at FSB tried various different (LM324, TL072 and LM13600) IC's and had some issues, but found it worked fine with the specified IC's.

Finally, re the value of R5 on the PCB layout (that's the 220k on the stripboard layout between v12 and x12). I ended up adding a switch to my build to toggle between 220k and 100k.

Rick

[sundgist]

I just built the C4 on vero. When the pedal is turned on i am getting a significant drop in volume. Also the regen knob does not seem to work at all. Has anyone built this on vero and got it to work? I know its not verified.

- The 6k8 resistor between r13 and s13 should be 68k, that will explain the volume drop.

Cheers for pointing that one out. Not sure how I misread that. Have updated the layout (refresh browser).
Am getting some time in building it at the moment.

[sundgist]

Kinda just got stuck into this and found it hard to stop.
I can now verify the vero layout as working. 

No changes other than correcting the 6k8 resistor to 68k.

Made a few subs as I had a few parts missing.
22uF used instead of 10uF for the two electros filtering V+ and Vref.
10k log used for Regen, gets quite resonant and peaky enough at max.
100k lin used for Depth with 100k resistor in parallel. Seems to taper nicely enough (before I put the resistor in, the LFO seemed stop LFO'ing from time to time when adjusting the depth?). I'm thinking of doing similar with the Speed pot, just to spread out the higher speeds a bit.
IC's used, lm13700, TL074, TL072
Plan on switching 220k R5 between two values.
I left a few extra rows on the bottom of my board, plus theres that empty space on the bottom left. Might just fit a Mill bypass in there.



Managed to have a short play with it with a clean guitar tone. I'm very pleased, having only ever used phasers on digital multieffects. This is quiet, clean sounding and usable. Will give it a good listen tomorrow with some dirt pedals when I can turn the volume up.

Next on the cards is an addon board with some extra switchable stages (will post layout here) and probably a few tweaks here and there as I get to know it a bit better.

Thanks for a really nice first analog phaser.

[svstee]

Kinda just got stuck into this and found it hard to stop.
I can now verify the vero layout as working. 

No changes other than correcting the 6k8 resistor to 68k.

Awesome! You just made my day. I can finally replace that crappy plastic cheapo phaser on my board! Thanks for the circuit Rick!

[svstee]

I just got a PCB I ordered from John Lyons before I saw the Vero and was wondering about the LED on the bottom right. Can I skip it and use a regular 3PDT bypass LED scheme? Board mounted LEDs always mess me up for some reason...

[frequencycentral]

I just got a PCB I ordered from John Lyons before I saw the Vero and was wondering about the LED on the bottom right. Can I skip it and use a regular 3PDT bypass LED scheme? Board mounted LEDs always mess me up for some reason...

You can skip it, but all it is is the LED's resistor mounted on the board conveniently close to ground, so ideal for regular 3pdt bypass schemes.

[svstee]

OK, I see it now. Thanks!

[svstee]

Built it and loved the way it sounded. My only complaint was that the Depth pot was working backwards, so I switched lugs 1 and 3. Fixed it and everything worked great for about 5 minutes, but then it started to produce this nasty, harsh, gated clipping whenever I played hard. Still sounds nice when I play with a real light touch, but crappy when I really lay into it. Happens regardless of there the pots are. Only changes are that I made r5 switchable between 47k and 220k, and I used the "Wet" switch.

Anyone else have this problem? Did I mess something up when I switched the Depth lugs around? They were where the layout said they should be when the pot worked backward (more depth when pot was turned left, CCW).

Thanks!

[sundgist]

Hadn't played with the wet only switch until now. Noticed I had put it in the wrong place and was removing the wet part of the sound rather than the dry.
I have corrected the layout (now v1.3 refresh browser) but if you have already built it using v1.2 here is v1.2a showing the corrections.



My apologies.

P.s. or maybe leave it as is if Dry Only is your thing.

[frequencycentral]

Built it and loved the way it sounded. My only complaint was that the Depth pot was working backwards, so I switched lugs 1 and 3. Fixed it and everything worked great for about 5 minutes, but then it started to produce this nasty, harsh, gated clipping whenever I played hard. Still sounds nice when I play with a real light touch, but crappy when I really lay into it. Happens regardless of there the pots are. Only changes are that I made r5 switchable between 47k and 220k, and I used the "Wet" switch.

Anyone else have this problem? Did I mess something up when I switched the Depth lugs around? They were where the layout said they should be when the pot worked backward (more depth when pot was turned left, CCW).

Thanks!

Are you sure you have the depth pot wiring correct? Is R8 definately 47k? Is R9 definately 4k7? You can try removing R8 altogether, I found that too low a value for R8 caused the issue you have, but removing it and just varying the resistance between the LFO and the Iabc inputs of the OTA sounds almost as good. Too low a value for R9 can cause permanent damage to the Iabc inputs of the OTA.

[svstee]

I just checked, and I can confirm R8 and R9 are the correct values.

I found that too low a value for R8 caused the issue you have, but removing it and just varying the resistance between the LFO and the Iabc inputs of the OTA sounds almost as good.

This goes over my head a bit, sorry. Where exactly are you talking about varying the resistance? How would I do that, add another pot? What would happen if I just pulled R8?

Thanks for all the help!