Phase 90 "vibrato" switch

[thermionix]

Ah man...

"Script" Phase 90 clone is in the works, parts are on the way.  Been planning on doing the "vibrato" switch, the simple one that cuts the dry signal before the base the output transistor.  But I'm starting to think it might sound better with a little dry left in, based on demos I've heard on Youtube.  Yes I have thought about a mix control, I know how to implement it, but I'd rather keep this a one-knobber, with maybe a small toggle on either side of the big knob.  Also I probably wouldn't have much interest in the "dryer than stock" mix settings if I had a mix pot.

So I'm thinking now to toggle the value of the "dry" mixing resistor between stock value 150k and maybe 560k or 680k, change the mix ratio instead of cutting the dry signal completely.  Seems this should work, but maybe it would be better to lower the value of the "wet" 150k mixer instead of raising the dry one.  Thoughts?  I get that it's a voltage divider and ratio sets the mix, but maybe it gets too loud if the resistance gets lowered overall.  Don't know if that makes sense.

The other toggle I'm planning on will be a 90/45 switch, or 4 stage/2 stage.  Seems like it would be worth doing, it's just a switch and a couple pieces of wire, but I haven't ever tried it.  I'd be interested in input if you have any thoughts on that too.  This is going into a 1590B with the GGG board, so I won't have much extra room, but I think two little toggles should fit.  My main goal is a straight script 90 clone, but why not add a couple more sonic options, you know, basically free and hopefully useful.

Thanks.

For reference:

[Mark Hammer]

If you make the dry mixing resistor 680k, that will push the dry signal well into the background, relative to the wet signal, yet still allow some dry to be mixed in.  If a toggle is used to strap 200k in parallel with the 680k, you end up with 154k, which is well within the 5% tolerance one would normally get using the stock 150k value.

This would be my own preference, in contrast to using any sort of mixing pot, where the ideal balance might be hard to replicate with any consistency.  On my own builds I just cut the dry feed entirely.

What you will find for vibrato is that the audibility of pitch wobble depends very much on speed, particularly since it is a fairly modest pitch wobble, in comparison to a flanger or chorus.  One of the implications is that vibrato "wants" a smaller/lower pot value for the speed pot, in order to facilitate dialing in usable speeds.  In service of that, consider using a DPDT toggle switch to go between vibrato and phasing, and simultaneously add in a resistor in parallel with the Speed pot to drop its effective resistance.  I'd suggest using 82k-100k.  You'll find that the last 50k of the pot are where the usable vibrato speeds are located.

[thermionix]

Thanks for the input!  I had been looking at RG's Phase 180 where he used a 200k mix pot with a 47k fixed resistor at either end, so in either extreme it's basically a 5:1 mix ratio, which led me very roughly to 680k:150k.  Then season to taste I suppose, because I have no experience messing with this mix.  In online demos I watched, it just seemed a little more musical, maybe more Univibe-ish, with a little dry left in the mix.  But maybe 100% wet would suit me better once I hear it in person, I don't know.

I probably shouldn't admit it, but I'm really hoping to avoid breadboarding this before building.  Just looks like a pain in the ass, but I may reconsider.  I think my JFETs are good to go.  I got 50 2N5485s last week, and measured them via the "quick and dirty" Geofex method (NOT trying to fire up that debate!).  I got five quads with <1% extreme spread, and a sixth with <2%.  Seven nice pairs in addition, not bad for 50 JFETs I think.  My quads all sit in the -1.5 to -1.8v range, so I've got it in my mind that I should be able to use any of them with the stock 5.1v zener.  But I will have other zeners on hand if needed.

I get what you are saying about the speed pot value as it relates to vibrato, but I will probably keep my switching simple because this will all be pretty cramped in a 1590B with the GGG PCB.  I might even skip switches altogether, just gotta see the fit of everything once the rest of the parts get here.

[Mark Hammer]

The switch I suggested is no more complex than using a DPDT toggle instead of an SPST.  The only "complicated" part would be that the switch would be wired up to have "opposite" effects/outcomes.  So, pushed to position 1, it would place the extra resistor in parallel with the 680k to achieve "normal" phasing, at the same time as it lifts the resistor placed in parallel with the speed/rate pot to achieve the wider range of phaser speeds.  Flicked to position 2, it now lifts the  parallel resistor that converts phasing to vibrato, and simultaneously adds a resistor in parallel with the speed/rate pot to reduce the speed range from the extended range suitable for phasing to a medium-fast-to-fast range suitable for vibrato.  Note that this has no effect on the maximum speed, only on the minimum speed.  If your 1590B can accommodate an SPST for producing vibrato, it can accommodate a DPDT to produce speed-compensated vibrato.

[thermionix]

I understand but it's still more wires, another resistor, slightly bigger switch, but more than anything right now is that I ordered 2 SPDTs and don't have any DPDTs on hand.  I can always change the switch in the future if the speed knob issue bugs me enough I suppose.  And there's still a chance I won't include any mods.  The PCB is based on the original, barely fits into a 1590B, and covers over where the pot and any switches would go.  Mounting controls gets complicated and wires get long.  Jacks go under the board too, wired.  I'll figure all that 3D stuff out when the parts arrive though.

What about the 90/45 switch?  Do you think that's worth the trouble?

[Kipper4]

Probably not mate.
Once you have heard the 90 compared to the 45.

[thermionix]

I figured that might be the case, but I've never played a 45.  I've probably played a 90, honestly I don't remember, but that sound is so familiar.  I could switch in feedback instead, "block" mod.  Don't know if I'd use that.  Maybe with a bigger resistor.

[Mark Hammer]

The 45 and 90 are different in more ways than the use of 2 vs 4 stages.  The 45 includes a network around each FET to provide some immunity to distortion and also has no feedback path.  It also uses a lower speed-range cap value (10uf vs 15uf in the P90).  One might suggest it is optimized for faster speeds.  That's not wrong in any sense, but suggests that merely tapping the signal after 2 vs 4 stages does not accurately replicate the two pedals in all their functionality.

That said, tapping after 2 vs 4 stages can yield something musically useful, and that's the goal here, not merely replicating a circuit down to the last little detail.

The 4-stage version does yield a very nice vibrato.  On my own builds, I like to include an "offset" control in the bias path that can move the range of sweep upwards or downwards to yield very different feels, from gurgly to swirly.

[thermionix]

That said, tapping after 2 vs 4 stages can yield something musically useful, and that's the goal here,

Right.  I say "90/45" seems that's what most people call the mod, but 2 stage/4 stage is more accurate.  If it's not something I'd use, I'd rather not include it.  I'll experiment some before boxing up at least, before I drill any extra switch holes, if I don't just breadboard the whole circuit.

I can see a second build in the future, in a 1590BB with all the bells and whistles.  One simple yet cool idea I saw in a youtube demo was dual speed controls on a footswitch.  That will definitely be included if I do a BB build.

[pinkjimiphoton]

if going for more of a vibe, the 2/4 stage switching is actually kinda cool.
i think it does a better "vibe" at 2 stages. subtler.
the 4 stage is cool to be able to switch to (i used a stompswitch) and adds the possibility of feedback to the equation that you can't get with the 45.
i found (in part thanks to mark's advice before) that decreasing the wet side of the mixer and increasing the dry side definitely helped. i went to 100k on the wet side instead of the 150k specc'd and it seemed to "focus" the phase better... at least to my ear.

[thermionix]

Well this is built.  And it works!  After getting the rest of the parts in I found that the switches were a little tall for how I would mount them, so I went mod-free, just a straight script 90 clone, except with true bypass, LED, and DC jack.  I used all stock values, 3M9 and 5v1, etc.  First JFET quad I tried fired right up with a twist of the trimmer.  So another win for the Geofex matching scheme.

I'll try to get some pics, it looks cool, I did some...stuff...

[thermionix]

I let this cook overnight on a wall wart.  Mojo break-in and quality assurance, I suppose.  Spent some real playing time with it today, sounds wonderful.  Much more Leslie-like than I expected, musical and natural.  I haven't even touched the trimmer today, it must be at the sweet spot.

I found the combo from hell:  Guitar>script Dynacomp>script 90>blackface Fender w/ reverb.  It's the thickest clean tone ever.  It's what a JC-120 wishes it sounded like.


[pics in pic thread]