phaser stages daughterboard?

[pinkjimiphoton]

hey guys,
i seem to remember seeing an add on daughterboard for phasers to add more stages to them somewhere,
on vero, but i can't seem to find it anywhere.

anybody gotta link by chance? getting ready to build another phaser and was thinking it would be cool to add on a daughterboard for a few more stages.

thanks!

[paul.creedy]

https://www.diystompboxes.com/smfforum/index.php?topic=80111.20

http://tagboardeffects.blogspot.com/2014/06/mxr-phase-90-4-8-stage.html

any help?

[Kevin Mitchell]

Wouldn't we need to know what phaser you're asking about? 

-KM

[Mark Hammer]

Tonepad sells a daughterboard for an additional 4 stages of OTA-based phase shift.  I doubt that it would fit all that well with an existing FET-based phase shifter, though.

[pinkjimiphoton]

thanks guys,
yeah, basically i am getting ready to build another p45/98 <both, with a switch to go between them> on a guitarpcb.com dr phybes board.

i remember somewhere recently i saw a vero'd daughterboard with an additional couple stages, i can't seem to find it again, and google is beyond no help sometimes.

just thought it would be cool to build say, a phase 360 or something

[bluebunny]

Rick's Causality 4 phaser had options for a 2-stage daughterboard, IIRC.  I need to go rummage to find it...

[bluebunny]

Here's a couple of links from Rick's original thread.  First, the "latest" (2010!) layout:

https://www.diystompboxes.com/smfforum/index.php?topic=80456.msg736682#msg736682

And second, the daughter board:

https://www.diystompboxes.com/smfforum/index.php?topic=80456.msg734599#msg734599

[nickbungus]

Have you got the schematic of what you are trying to add stages to?

[Kevin Mitchell]

I recall seeing a schematic for a phase 90/180. Maybe that's what you are referring to?

Well I've found this. Could be what struck my memory;


Haven't seen a daughter board though. Could easily do one up in a matter of minutes.

-KM

[Kevin Mitchell]

Oh that reminds me! This morning I shipped out a Small Stone clone with 5 CA3094 chips. I love the hell out of that thing. I definitely prefer that over any MXR phaser. Shoot me a msg if you have any interest in those OTAs as I'll soon have a good stock of them.

I'm itching to lay out a 4-6-8 stage version of the beast.

-KM

[Mark Hammer]

The "secret" to the Small Stone is the shape of the sweep.  The "Color" switch changes three things simultaneously: the amount of feedback/resonance, the speed range, and the shape of the sweep.  In one position it bumps up the feedback, slows down the speed range, and changes the LFO shape to "hypertriangular" (sine at the bottom, triangle at the top).  In the other position, it reduces the feedback, speeds up the rate, and converts to triangular sweep.  If you have an early-issue unit, it also smoothes out the LFO as you turn the speed up past around 2-3hz.

Since Jimi is building a FET-based unit (MXR), the most straightforward way to add stages is to simply do what MXR themselves did in the Phase 100 (and Boss did in the PH-2 and RPH-10), and  make some fixed phase-shift stages.  No need to either buy or match JFETs.

Jimi, you like to experiment, so consider experimenting with adding fixed lead OR lag stages.  The more familiar phase-shift stage is the "lag" type, that produces more phase shift as audio frequency increases, maxing out at 90-degrees per stage.  The less familiar "lead" form swaps the resistor and cap positions, going to the non-inverting input.  This adds phase shift as audio frequency decreases.  You can calculate where you want the phase shift to start adding by simply treating C and R like any single-pole lowpass or highpass filter.

[pinkjimiphoton]

wow, guys, thanks so much.

i need to build another causality. i miss that thing. i gave the one i built to steve hunter <alice cooper, lou reed etc> for his birthday last year. i added an exp jack for an ev5 to it to control the speed. and i built it with all the baubles and beads, had i think 6 or 7 knobs on it.

this one is a guitarpcb board, they call it the dr. phibes
https://guitarpcb.com/wp-content/uploads/2018/06/BD_Dr-Phybes.pdf


its really just a p90 with a mod to split it to a p45. i was just thinking it would be cool to maybe add a couple stages more on a vero daughterboard, as i came across one surfing recently i can't seem to find again.

i really like the idea of adding the fixed stages to it. to me, that makes a lot of sense and should improve the phasing a bit too.

but i'm still searching. i have JC's phaser board here waiting for me to get to too, and i have jurgen haible's 20 stage phaser board here too awaiting the motivation to get to.

the p45/90 is just good for me cuz i can squish it onto my already way too stuffed pedalboard.

i will re-read this when i'm a little more awake.

[Mark Hammer]

Good.  One of the decisions to be made is where to insert the additional fixed stages.  There are a few choices to be made.  You could insert them on the output of IC2A.  This would provide a third notch, but keep the feedback limited to 3 stages, as per stock.  Alternatively, you could insert them between IC2D and 2A.  That has a pro and a con.  The pro is that the feedback now travels 5 stages, which can make it more intense.  The con is that the feedback now travels 5 stages, which can increase noise and runs a greater risk of oscillation.

The noise risk is cumulative across stages, but can be easily tames by sticking a cap in parallel with R15.  You can use anything from 2200pf to 1000pf.  Note that when noise is fed back, it gets worse; which is why rolling it off before it gets fed back is a good idea.

I find that, with >4 stages, the range of sweep starts to shift downward.  And since much of the guitar signal, as I like to put it, "lives in the basement", inserting a cap just before R16, can be used to roll off bass that risks honking, due to feedback.  With R16=33k, I'll suggest 15-18nf for that cap.

Speaking of the feedback cap, 33k is kind of high, compared to stock P90s.  You'll notice the difference, compared to no feedback (SW1 open), but you won't get the "big swirl" of a P90 unless you drop that resistance value a bit. If you do drop the R16 value a bit, make the suggested feedback cap a little bigger value, like 22nf.

The Phybes uses a 3M9 fixed resistor in the R23 position.  This was MXR's one-size-fits-all approach to sweep width, that would be reasonable for both fastest and slowest sweeps.  The circuit is capable of sweeping wider, if you reduce the value of R23 a bit.  Some issues had a value of 3M3 in that position, from what I understand.  This will give a wider sweep, more appropriate to slower, higher feedback, sweeps.  It's not a huge difference; maybe about 15-20% higher than where the stock sweep ends.

Finally, I find one of the most useful features is being able to adjust the range or "offset" of the sweep.  That is, where in the spectrum the notches and peaks are created.  To do that, replace R30 with a 510k fixed resistor, in series with a 470k/500k pot (variable resistor), so that you can adjust the current-limiting resistance between 510k and however close to 1M the pot brings you.  Set the pot to maximum resistance, and then adjust the trimmer for most gurgly sweep.    As you decrease the resistance, the sweep will move from the gurgly end to the thin and swirly end, with lots of useful stops along the way.  If you can't be bothered with another pot, just use the stock 1M resistor and a 3-way toggle to add in other parallel resistances for two more distinct ranges, or simply a plain vanilla SPST toggle for hi/lo ranges.

The P45 was intended to be a sort of ersatz Uni-vibe.  Placed ahead of an overdrive, you can get a sort of Trower-esque tone.  But I say "Let a VIbe be a vibe, and a phaser be a phaser."

[pinkjimiphoton]

holy cow, thanks mark, lotta really good info and suggestions.
right now i'd debugging YAFF... for some reason, whenever i do a pnp fuzzface it NEVER works out of the chute!!

i will re-read this when the sun goes down and i get outta my coffin. its tough to be a vampire in this day and age

i like the mod ideas a lot. i gotta print the build doc and this thread so i can integrate stuff fairly easily.

do you think if i add the fixed stages it will prevent doing the p90/45 switch trick? i'm fine with that, really if i need to forgo it.

i'm really doing this mainly cuz i'm too lazy to build another causality at this time. but man, thats my fav phaser of all.

i DID take your advice years ago, and have suggested it to many since... a phaser DOES sound better tickling a distortion than AFTER it. so much cooler and more "organic"...

like the diff between some good peyote buttons and some blotter acid. that may not mean much to some folks, to some others, it will make a lot of sense.

imagine drinking and comparing "real water" to "artificial" water.

errrr...

think sweet, natural delicious well or spring water compared to new york city tapwater. that should get it across.

hopefully later i can get started. thanks again brother mark, and marc, and everybody else

[Mark Hammer]

Note that a real P45 has an additional network around the JFETs that make it more immune to distortion at higher input levels.  It also lacks any feedback, because it only has two stages, and sending feedback from the output of stage 2 to the input of stage 2 doesn't really do much.  So if you DO attempt the 4-into-2-stage mod, remember to cancel/lift the feedback path.

On the other hand, one does have to wonder what running 6 stages (4 swept and 2 fixed), with feedback from stage 6 to stage 2, and tapping the phase-shift/wet path at stage 2, would sound like.

[RickL]

I did a 4 stage/2 stage mod on the Joyo phaser I just bought (pretty much a phase 90 copy) and can hear the difference between two stages and four stages without the feedback, but not with it. Note that the feedback still goes from the output of stage 4 to the input of stage 2 even though the output of stage 2 is what is mixed with the dry signal to get the phase sound. I kind of expected 2 and 4 stages to sound different, even with the feedback from stage 4. I bet you could see the difference on a scope, but I can't hear it.

[Mark Hammer]

Thanks for that, Rick.  Good to know.

[pinkjimiphoton]

Note that a real P45 has an additional network around the JFETs that make it more immune to distortion at higher input levels.  It also lacks any feedback, because it only has two stages, and sending feedback from the output of stage 2 to the input of stage 2 doesn't really do much.  So if you DO attempt the 4-into-2-stage mod, remember to cancel/lift the feedback path.

thinking maybe a second footswitch? i could use a 3pdt and switch the stages in and out with 2/3rds of it and use the remaining 1/3rd to cancel the feedback at the same time easy enough for even ME to figure out. i seem to remember it popping a little last time. no biggie tho. i like multiple footswitches. i can put the feedback on a toggle on or off and use the footswitch to kill it in p45 mode.
makes it more idiot proof, which with me is a good thing. [/quote]

On the other hand, one does have to wonder what running 6 stages (4 swept and 2 fixed), with feedback from stage 6 to stage 2, and tapping the phase-shift/wet path at stage 2, would sound like.

you have a sickly wonderful mind, sir mark. i like the idea a ridiculous amount, but i don't know if i have enough of the proper jfets to pull it off. i bought a literally perfectly matched quad from barry <actually, i think he may have thrown them in gratis, he's like that> and have 5457's and j112's <errr... j113? not in front of me, so i forget lol> but i think the vgs is just too high to be any good for a phaser. i probably just called it the wrong thing... the cutoff voltage. seems like the ones i have wanna see about 3 volts or so, the quad i have is about a volt and a half if memory serves.

so couple questions...

if i can find some close matches with the jfets i have, does it matter if the fets are different as long as the voltages are the same? like, say i could find something i have here that reads about the same, and can find say 2 or 4 of them, could i use them in conjunction with the matched set i have already?

like... to an electron a resistor is a resistor pretty much... i can't see jfets being the same, i generally avoid anything to do with them if at all possible

also, does it matter if i used a dual oa with the quad for the stationary phase shift stages? trying to see if i can make it work with this board and work up a daughterboard and mod for it. doesn't seem like it would be too stiff to do on a tiny piece of vero or perf.

where would be the best place to add the stationary stages? before the "active" phaser, or after it? perhaps one stage before, one stage after? does it need to have a symetrical number of stages to maintain proper phase coherence from input to output of the audio signal itself?

too many questions, sorry...

i dunno if its even worth messing with for this build, may be better to do on the old pos bb.

thanks for dealing with my madness
ya'll rock

[Mark Hammer]

You realize that FETs are not required for the fixed stages, right?  Or have I misunderstood you?

[pinkjimiphoton]

i didn't realize that until i looked at the thread again

but still... before? after? does it matter?

remember here, i'm a moron

reminds me of a tagline is used to use

if electricity comes from electrons, does morality come from .....?