Phase 90 LFO potentiometer value

[ElectricDruid]

Yeah, I've been caught out once trying to solder a circuit that was powered up. Like you, it frazzled some stuff. I never quite understood why, but it seems like the end of a soldering iron has a voltage potential, and if that disagrees with whatever you touch it onto, you can get into serious trouble. Since then, I've been more careful to make sure things are turned off. I suppose I figured "what the hell, it's only nine volts! How wrong can it go?!". "Quite Rong" is the answer to that question...

T.

[Myampgoesto12]

I fried a 386 IC doing that as well. Safer to just shut them down hah.

Anyone ever experiment with the different feedback paths on a P90? Just got my depth control added and I'm wondering if there's a good reason not to add the FB switch (1p6t). I'm totally digging this thing as is with no feedback in the phase section, is why I ask.

I think the less pronounced tone aids the effect when placed after my overdrives. Before OD it seems to act a little more like a auto-tone switch sort of thing. I've had a similar experience with flangers before dirt. Just a less expressive sound for me when placed early in the chain.

[pinkjimiphoton]

i tend to like phasers without a lot of feedback too, but i love a phaser before dirt. totally different animal, more like an animated wah wah to my ears.

[Myampgoesto12]

i tend to like phasers without a lot of feedback too, but i love a phaser before dirt. totally different animal, more like an animated wah wah to my ears.

^^ that's what I was hoping for, but I bet those results depend entirely on each individuals' rig. I use an overdrive pedal stacked with a distortion pedal for my main dirt tone, they aren't set to ignorantly high gain but the extra sustain is lovely hah. So that may be why I don't dig the phase before them.

For my rig, that extra whoosh that some folks don't dig about placing it after dirt adds a bunch of depth that isn't present when placed before. And the depth control really can dial that back. Though the tone is still quite different than when placed before.

Btw the depth control mod I added isn't in the schem I posted. I used a mod found on this site -now I can't find it to link it- but I replaced R17(1M) on that schem with a 500k linear pot as a variable resistor, with a 470k AND a 33k resistor in series with the pot, wired as 470k->500kpot->33k, if it matters.. The mod I found here didn't have a 33k in it, but I wanted to be able to dial it to ≈ stock so I added it. It really does work great. The minimum setting is just a pinch to little depth, and the adjustment is smooth. I just can't wait to emplament the manual control!!

[pinkjimiphoton]

the frequency thats being swept really matters before distortion. i stack up a lot of dirt, too.

if ya like phasers, try rick holts causality. wicked easy, and sounds bloody fantastic. tickling dirt with a phaser
was suggested to me by mark hammer, and man, he nailed it. that said, to me, seems to sound best in the bass frequencies before dirt.. instead of getting swooshy wooshie, it just kinda... seems like its breathing. really trippy

[Myampgoesto12]

 I'll eventually get around to other units, this one was sort of an investment hah so it'll have to do for a while. I'm not gigging right now so its tuff to throw a lot into buying/building these things. I absolutely love it though.

I beleive I'll leave this thing with no feedback for now, if not for the reasons above alone, because I'm not experiencing any NASTY clipping from it and its not a crazy mod to add the 1p6t(off positions on eachside of the rotation.) It'd just need to be made cleanly.

It does have a little bite when I really smack the strings, but my style of playing calls for that.

[Myampgoesto12]

 Upon further playing, I've found the stock .01 cap in the LFO to work sufficiently with the limited range of the hot potz. Faster extreme at toe down position. Not not quite the speed as a stock unit I'm sure, but its faster than my left hand vibrato hah. I think this raised the rate of the heel down position as well, but barely. Still a usable range imo. The taper of the pot is beneficial I think, but I have not measured the resistance though out its range, playing it by ear.

So per-pot value:
-Higher cap value = slower rate
-Lower cap value = faster rate (I don't think it should be lower than .01, just a gut feeling hah.)

I have the switch that will be used for the manual control mounted, but not wired up yet. Getting there! When I get the hooked up and workable I'll be back!

[Myampgoesto12]

Ok, I'm going to stick my neck out for a bit of educated guesswork. No promises of total accuracy!

I would guess without having tried it that if you take the pot out a of the typical Schmitt trigger LFO (something like this one below) that the integrator triangle output will finish up at one of its two extremes, and probably more extreme than it manages when it's running as a triangle - basically it becomes a comparator with one input tied to ground and the other input open. We can assume that open input won't be perfectly at ground, so it'll fly off to one rail or the other.
That's my best guess, anyway.



You might get "a phase shift" without the pot (since the output is still at *some* voltage level, but you won't get a *moving* phase shift, so it won't be much you can hear.

Jimi, the Univibe LFO is a completely different beast. It's a phase-shift oscillator based on transistors, rather than a Schmitt trigger/integrator oscillator. I don't know a lot about it, and I'm afraid I have no idea how you managed to set the thing on fire. Are you sure you didn't squirt lighter fluid on it?

T.

I have installed the 4pdt control switch finally, though it is not fully wired up yet. The treadle still only controls the rate right now. But when the switch is flipped to remove the pot and Zener Bias voltage from the gates, the circuit locks into whatever "position" the phase sweep is in at the time of the switch. Interesting find I feel.

This won't happen when I get the manual pots hooked up, but it is a means of obtaining a locked phase tone if one does not wish to install, or have 3 pots to create the manual control. A downside to it is you must wait for the sweep to reach whatever desired tone you want, and then flip the switch.

This effect could be done with only a 3pdt switch wired as "on-off" for the pot and Zener Bias Voltage.

[Myampgoesto12]

I've been doing some more digging on here and other general searching and have found that everyone is saying C7(15uf) determines rate, I misunderstood the post earlier about upping the cap value to match the new pot value. So I swapped the .01 cap instead of the 15uf cap. As I stated before I have put the stock .01 cap back in place.

Does increasing this (c8 .01) cap increase the range of the voltage swing? I'm finding that this pedals sweep feels a little tight now, like depth-wise, especially at the faster range.. If c8 does control the Vswing range of the LFO, that may explain this tightness to me, and possibly the perceived speed increase once I changed it back to stock.

Another reason that I ask is because I rebiased the trimpot and have found tones on both sides of the "sweet spot" of the trimmer that the LFO can't reach once the trimmer is set to its best tone.

If c8 can add depth when increased then I'll do that and lower c7 for a faster rate.

Any thoughts or answers?

Thanks everyone for dealing with this topic hah

[ElectricDruid]

Sorry, what schematic are you referring to now? C7/C8 doesn't mean much unless I'm looking at the same thing you are, and I got lost somewhere along the way.

T.

[Myampgoesto12]

My schem is posted earlier in this thread, but its the GGG schem that I added mods to. 

Sorry to make this confusing hah. As it sits now the circuit is stock except to the pot. That really doesn't matter since the series resistance it adds in the LFO only slows the rate down as more resistance is added anyway.

I'd like to know of a way to increase the depth BOTH above and below the current limmits of thw LFO since the control I added only cuts depth when adjusted.

I can hear while adjusting the bias trimpot that there is a range above and below the sweep of the LFO. But when the bias and set to the best performance of the LFO these two extremes aren't swept to. So I'd like to increase the sweep range of the LFO. If this type of LFO can't be increased it isn't the end of the world, just trying to dig around for info.

[ElectricDruid]

Ok, this one then?:

http://www.generalguitargadgets.com/pdf/ggg_p90_sc.pdf

Increasing the ratio of R5 to R4 will give you a wider LFO sweep. Make R4 less and R5 bigger for a wider sweep. It'll change the frequency range too (since it'll sweep further before flipping back the other way) but you already know how to tweak that with C7/R21.

Note that there's a "natural limit" to this when the op-amp starts to clip, which will be somewhat before you get to 0V and 9V trough and peak, depending on the op-amp type. I usually reckon on 2V to 7V, but in practice you can often do a bit better than that. You could stick a 470K pot instead of R4/R5 and see how far you can push it. Then pull the pot out (carefully!) and measure it.

HTH,
Tom

[Myampgoesto12]

Im sorry, i dont understand..

R4 and R5?  Those resistors are both 22k,  between the Sources and the Opamp +, parallel to the Drain and Opamp +, in the middle two phase stages, in the GGG schem. I know the phase shift occurs because of the resistance between S and D being shifted by alternating voltage at the gates.. So why those two specifically and not say R3+R6, or 3+4, etc...  Is it a phase thing, (go figure hah) between those two stages?

I don't mean to be difficult at all, I just want to understand, and perhaps this can help anyone else plunging this deep into these things.

I've been playing with pedal placement after adding the feedback resistor on a switch. I'm feeling better about the tone with it before my drives, but it still seems like a limited sweep.

Hooked up my manual control!! I have two 100k trimpots, as variable resistors, one on each end of the HotPot to dial down its range. Its a nifty thing, but the trimpots seem to not limit the HotPot range enough. Will have to try higher value trimpots at a later time. As it is, I can only dial in a toe down tone, the heel down is unaltered by adjustments, and is also beyond the transistors' range it seems. This (and also the taper) makes most of the swing happen in the upper half (from heel to toe) of the manual sweep.

The manual sweep feels smoother when the pedals placed after my ODs, but that's the wooshier tone, along with the volume swing to go with it hah.

Still more to do, as always.

Thanks again. Learning a lot here(and under the hood)

[ElectricDruid]

Sorry, my bad. Apologies, that's a silly mistake. I got the references mixed up with another schematic I was looking at.

On the schematic I posted, I meant R25/R23. Decrease R25 and increase R23.

These two resistors set the level at which the comparator op-amp IC6 switches state from positive to negative. If that happens sooner, C7 doesn't have so much time to charge up/discharge. If it happens later, it has more time, and you get a bigger swing either way.

[Myampgoesto12]

Ah ok! Things happen, no biggie. Its amazing that such a simple configuration of components(this LFO) has such control potential yet is hard to find info on. In really thank you for your help.

Fun fact, the manual control has a bit of a laggy climb in the sweep when going from heel to toe positions. Maybe this is because the HotPot swings too far on either side of the effective gate voltages. Must still tinker.

Fwiw the best sounding point on the bias trimmer is quite far along its rotation, around -but not quite- 3 o'clock.

I may need to apply swittched parallel resistance across the HotPot after all to help limit its sweep in manual mode.perhaps two 47ks one across pins 1+2 and another across 2+3, but first I'm going to try larger trimmers.

[Myampgoesto12]

Dredging up this old topic, sorry. I've just added a couple of things to this phaser.

Asentioned in my post about the tremolo I've gotten the 470k pot for this, added a switch activated trimmer  in the feedback loop, and gutted the manual control ( the 470k made this useless) and used the switch to turn the dry signal on and off for the vibe mod. This combined with the "depth" pot is pretty cool, a little bouncy or sea sickish, but cool.

Ive found through some digging that this depth control ( 470k and a 33k in series with a 500k pot replacing the 1m resistor from Vbias) is more like a fine tune for the bias. That's to this forum and some time that is. But it does indeed make the vibe more usable, less OYOYOYOYOY sounding

[Myampgoesto12]

Sorry to bring this topic back up, but I have another question that searching here or anywhere hasn't specifically answered.

I did some video searching on the phase 90 to compare mines sound to the real thing.

I have moved the phaser in front of my distortion pedal, but it seems i can't dial my phase 90 in to sound like a stock block logo, before or after or without the distortion pedal, I kinda like it, but I'd also like to have the faster rate not sound boingy when playing chords. I don't have a way or recording right now, or a way to test my transistors...yet. When not playing and just letting the 60hz hum buzz I can hear the sweep going through quite a range.

So I ask what type of side effects can come of poorly matched transistors? It is deffinately phasing, but it seems to sound a little more virbrato-y to my ears dialing back my 1m from the trimmer sort of dums it down but it also makes the phaser sound weak. Could this just be interaction with my dirt pedal?

Chain is
-EC1000 w/ Duncan custom bridge pu, phatcat neck pu
-TBP crybaby
-Phaser
- MXR Distortion 3 nodded for more bass and treble then MXR 10 band- both in a TBP loop
-chorus not always on
-delay not always on
-Outlaw boost

Thanks for the help. Like I said this phaser is nifty, but its definitly different than the real deal.

All suggestions welcome!

[Myampgoesto12]

Finally got around to adding an external pot to a just the 470k resistor to set the sweep depth(LFO voltage swing range?)! Its pretty cool. I used a 250k linear pot as a variable resistor with a series 220k resistor.

This does slow the rate down because the LFO has a longer swing, but I'm working on a couple of ways to compensate.

At the max setting (not resistance) I absolutely love the sweep at the slow end. I can tell it will get super wobbly if/when I manage to get the fastest rate back up to where it is at the stock swing setting.

So to avoid the super warble, I'm thinking of wither trying the whole physically mounting another pot sharing the pinion gear with the rate pot, or perhaps another rack an pinion all together at a different spot in the pedal. I'll also need a new bracket for the new pot. All this in an effort to change the rate and the swing simultaneously.

May need to make the hole bigger to accommodate the new pot, but I'm still looking for a pot to used before going that far.

Edit: could use another 470k with parallel resistance to bring it to the right value. The taper may not matter since its the two ends of the treadle movement I'm most worried about

[Myampgoesto12]

I just found out while dong this latest mod that my rate pot wasnt turning all the way at the toe down posistion. Made that adjustment and it more or less made up for the difference in rate. And it's a pot so I still have that crazy speed available by returning that to stock resistance.

I just decided to see if I could get the faster rate back up to see if I liked the intensity that that rate, works for me so I'm digging it.

I also added a switch to swap the first two phase stage caps with the common "univibe" mod. Just went for the first two because they were the only caps I had laying around. May do the other two with another switch later. I totally love it. Subtle difference but it puts this thing really close to what I want!

[Myampgoesto12]

Since this thread was resurrected

https://www.diystompboxes.com/smfforum/index.php?topic=111336.0

I'd like to mention that after reading Mark Hammers post about the 3m9 resistor being the sweep limiter, that in my kit this resistor is the only one that isn't 1%. This and the fact that the caps in the phase stage are .047 could be what made my unit sound a little weaker than an actual block logo model.

After some short depate I've decided to stick with this suggestion

I meant R25/R23. Decrease R25 and increase R23.

These two resistors set the level at which the comparator op-amp IC6 switches state from positive to negative. If that happens sooner, C7 doesn't have so much time to charge up/discharge. If it happens later, it has more time, and you get a bigger swing either way.

Because it does limit the faster rate, this makes a more usable range in this wah enclosure. It does make a "choose between wide range and slower rate, or narrower range with crazy fast rate" choice, but it is a pot I added so there's a smooth way to choose, hah.

Just wanted to throw it out there for anyone else looking for answers like this