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

[Xide88]

Just built it and it doesn't working right  

1) It is phasing only at high values of speed. with almost all values of range and  all another at 0
2) other pots are working, but speed must be high for phasing, almost maximum
3) with all pots maximum or speed, width, shape at maximum  i can hear a thumping sound, i hear that LFO is working, but only at speed almost maximal,
but if i try i can hear that lfo is working even at minimum of speed, but it isn't phasing  

i check all voltages and they are almost similar to Rick voltages!

Where is the problem?

I use TL072 instead of NE5532, сan it be a problem?

[Xide88]

bump

[frequencycentral]

As the opamp is different that *may be* the issue. I never tried a TL072. Though I would imagine there shouldn't be too much difference. I don't have a Causality here at the moment, so I can't try a TL072. But it's of course possible there could be an error in your build?

[Xide88]

I will try make it again and try to find NE5532 

[Xide88]

Rick, any news about Causality 6 or it's PCB is verified? 

[frequencycentral]

I'm in the middle of a big build at the moment, as well as some client builds, as soon as I'm done with them I'll be verifying C6 with all the features mentioned in this post. So about a month.

[Xide88]

Thanks a lot, Rick! 

[kristopher612]

Hey there.  i just finished up a build of this circuit with the 2 stage daughterboard and phasefilter mod.  This is a beautiful sounding phaser, and i just wanted to say thanks for it.  oh, i also used a modified version of the small clone LFO.  i saw earlier in the thread that there were issues with the added stages, but it worked fine for me.  could it be maybe the current draw of the ICs being used?  i used UA741s for the audio op amps and a LF358 for the LFO and didn't have any issues, so i thought i may may throw that out there for anyone who might care. 

[frequencycentral]

Kris, that's great! Tell me about the filter mod - how did that work out? What cap values did you uses? Did you implement any type of switch hitter or inverter for lowpass/highpass. Would also be nice to see a schematic of the LFO you used. And generally a lot more info (and PHOTOS) of your build. Congrats an well done!

[kristopher612]

the filter mod worked out really well.  just as Mr. Hammer has said numerous times it's somewhere between filter phase ands tremolo especially with the dry signal cut.  i didn't think to look at seeing if switching between HP andLP was even an option.  i will need to rehouse it at somepoint so maybe then.  the box is pretty simple really since i knew there would need to be a rehousing in the future.

here's the LFO. the mods basically made it a littler bit faster on the fastest end and the depth takes it from barely a warble to full on phasey goodness.  i may have the pot lugs for the depth control backwards in the schematic, it's just set up as a variable resistor that goes to 0 ohms for max depth. 
http://dl.dropbox.com/u/23916647/small%20clone%20lfo.png

[kristopher612]

i forgot to answer this.  i used the .033 caps called for in the schematic.  when i rehouse i will probably add the range control for even more versatility.  as it is now in phase mode i get a really nice wowwowwow thing going on, similar to a roland jet phaser.  haven't tried it with any dirt yet, but hopefully i will get to soon.

[frequencycentral]

Ok, I'm just putting together the lastest iteration of Causality on a C6 PCB. I'm using this build as a test bed for a few things, based on this schematic:

http://www.diystompboxes.com/smfforum/index.php?topic=80456.msg740457#msg740457

What I've done so far:

• Replaced the vref voltage divider with a 78L05 - it was bothering me that the vref fluctuated with the LFO - now it's rock solid.
• Implemented the 4/6 stage switch - really nice variations available here.
• Implemented the regen pot as a mix between odd and even stages of regen, null in the middle, odd one side, even the other side - works really well and again some nice variations are available.
• Implemented the phaser/filter switch - not really happy with this yet. I'm gonna try drastically reducing the filter stage cap values, as most OTA filters I'm aware of have their filter caps in the pF range - Oberheim SEM is 300pF, Korg MS20 is 1nF, Oscar is 1nF, Wasp is 1000pF.......

EDIT: I just realised, having scanned a few VCF schematics, that the filter mod should send the cap to vref, not ground........

What I haven't done yet is work out how I'm gonna do the HP/LP thing. My gut tells me a switch hitter circuit will work here, as it's all about phase cancellation. I sure hope I can get it working how I want, as the HP/LP is already etched onto the enclosure....

Here's a couple of work-in-progress shots.......

[Mark Hammer]

While it is certainly easiest to implement a phase-filter mod using the existing caps, by simply "flipping" one end of each cap to either ground (for lowpass) or the input (for allpass), you may not necessarily like where the lowpass range is set to.

In such instances, it may be preferred to have two caps with one end connected to pins 5/7 or 10/12, and connect the one value when using that stage as an allpass section, and the other when using it as a lowpass section.

Again, that isn't a necessary addition, just a means to nudge the lowpass frequency range over to where you might feel you prefer it.

Of course, for those who like to have too many switches, there is also the option of being able to select different caps for the lowpass range.

[frequencycentral]

Yes Mark, I think I'll go with the switched caps idea you mentioned. I've run out of playtime today so I'll get onto that tomorrow.

Incidentally, do check out some vintage synth OTA filters - the filter cap always goes to ground - but of course synths use bipolar supplies, so it needs to be vref in pedals. Mine's working much better now I've used vref.

The other unexpected feature I just found is a wide range of new sounds are available in phaser/filter mode because of the way I've got the regen hooked up - still getting my head around what's actually happening, but I like it. Of course, I can also switch out the phase stages and just use the filter stages more variation. Nice to have options........

[Mark Hammer]

Hadn't checked in on this thread in a while.  Nice evolution of the circuit.  That's a clever trick you have with the regeneration being variable from inverting to noninverting.

I see you have the dry mix set to 50/50 when the dry mix pot is at max.  Consider lowering the value of the dry-mix mixing resistor to 22k or even 18k, as a means to make the dry sound dominant (when you want) to render the phasing effect subtler.  You still get the option to turn the dry level down to produce vibrato effects, but you now have the option for subtler effects when all you want is a little shimmer.

P.S.: Doesn't the absence of any cap in the regen path cause problems?

[merlinb]

I see you have the dry mix set to 50/50 when the dry mix pot is at max.  Consider lowering the value of the dry-mix mixing resistor to 22k or even 18k, as a means to make the dry sound dominant (when you want) to render the phasing effect subtler.  You still get the option to turn the dry level down to produce vibrato effects, but you now have the option for subtler effects when all you want is a little shimmer.

Better yet, sling the mix pot between the output of input buffer and the output of the last filter stage and you can blend between 100% dry to 100% vibrato, with any blend of phasing in between!

[Mark Hammer]

Do keep in mind that the output stage is an inverting op-amp.  So, reciprocal adjustments to the input resistor for the wet or dry side also have implications for the gain of that stage.

Consider, with input resistances of 27k and a feedback resistance of 15k, the stage provides some attenuation.  If the input resistance for either side dips below 15k, then the stage starts to add gain.  And once you have gain implications, then you need to add an output volume pot to achieve the desired effect/bypass balance.  That's the primary reason I suggested what I did; it just ends up getting you 90% of what you want but with much less nuisance than trying to get 100%.

[merlinb]

Do keep in mind that the output stage is an inverting op-amp. 

Are we looking at the same schem? I see a non-inverting output stage: http://www.diystompboxes.com/smfforum/index.php?topic=80456.msg740457#msg740457

[Mark Hammer]

Bah!  You ARE correct.  I was looking at the Ross Phaser, not the Causality output stage.   

Carry on!

[frequencycentral]

The phaser filter experiments continue. Even with very small filter cap values (1n), I'm still finding that the filter is doing it's thing way below where the phaser wants to play. So I've referenced the filter OTA's (stages 3 and 4) Iabc inputs to ground with a 10k resistor (to raise it's initial frequency) and referenced the phaser OTA's (stages 1 and 2) Iabc inputs to +ve with a 4k7 resistor(to lower it's initial frequency). Now it's just a matter of selecting the correct phaser cap values. As I've fkd about with stages 3 and 4 initial frequency I now have to raise the phaser caps values to get good phasing. Likewise, stages 1 and 2 having a lower initial frequency now need their cap values lowered. I've just installed sockets for the caps, so tomorrow I'll have myself a little cap frenzy. All this before I even think about highpass/lowpass.....