MXR Phase 90 - wet/dry mix?

[ESPm2M]

I realized that I like the actual phasing of my Phase 90 but I absolutely hate how wet it is and it near drove me to sell it on a number of occasions.

I searched the forum but didn't really come across what I was looking for ...  I'm sure it is possible to mod a recent MXR Phase 90 with a wet/dry mix pot, but can someone suggest how this might best be achieved?

thanks

[Kleber AG]

If you had not did that yet, try removing R28 and you'll get a more pleasing phase, less wet, more subtle and less distortion. Probably not needing a wet/dry mix.

But if you want the wet/dry mix pot, check this:
http://www.geofex.com/FX_images/p180plus.gif
There you can see the 200K pot for the wet/dry. It's not easy to find a 200K pot so you can do that with a 100K pot and the outer resistors 100K each one instead of the two 47K ones.

But that will go from clean to max-phase at middle and at the other end a kinda vibrato.

Kleber AG

[vdm]

hi there,

If im not mistaken the mixing resistors on both the phase 90 from tonepad and geofex both have two 150k resistors mixing the signals.

im not sure but i would suspect decreasing those resistors lets more of that signal through.

as the total resistance is 300k, i would suggest using a 250k linear pot which may have just enough of a decrease in resistance that it won't go totally clean or totally phase signal, which is probably what you want anyway.

Personally i prefer a switch here to go from standard to 'vibrato' mode where the clean resistance is around 200-250k and the phased resistance is 0-50k. just tune it to ear.

good luck

trent

[ESPm2M]

thank you both.

Looks like I'm going to have some fun modding it over thanksgiving break!

[ESPm2M]

... is it possible to Univibe a Phase 90?

[Mark Hammer]

1) Possible to "Univibe" a P90?  Yes.  You can do this to essentially any 4-stage (and sometimes two-stage) phaser.  The cap values in the actual Univibe design are not "magical" in any sense, but they distribute the phase shift more evenly across the spectrum, and that's a big part of what delivers the characteristic sound.  Something close to the values you see in the Univibe should get you something close to that sound.  Many folks have swapped the cap values in Small Stones and Ross Phasers for the Univibe values and gotten excellent results.

2) "Drying out" a P90.  Two broad approaches to wet/dry mixing in modulation pedals.  One is to provide a means to vary both wet AND dry balance/level.  That is the method shown in the GIF linked to.  The other approach, which I personally tend to opt for, is to vary wet level only in continuous fashion, and use a switch to cut out dry on an all-or-none basis.  Why?  Lifting the dry signal entirely creates another kind of effect.  Having SOME dry signal dilutes that particular effect, and while it provides another musically-valid sound, most folks (myself included) don't find a lot of use for it on a day-to-day basis.  In contrast, most folks can find a reason to trim back the effect intensity by reducing the wet content.  Fortunately, that's a much easier task to accomplish.

Leave the 47k resistor coming from the output of the first op-amp in place as is.  Change the 47k resistor from the last phase shift stage to a 39k resistor, and wire up a 250k pot as a variable resistor between the free end of the new 39k resistor and the mixing point at the base of the transistor.  This new arrangement will let you go from just a little more wet than dry, through the perfect 50/50 balance to noticeably less wet than dry.  It won't achieve NO wet signal, but then that's what the bypass control is for isn't it?

Variations[/u]:  Where the cancellations happen most can be influenced by sticking a small-value cap between the output of the last phase shift stage and the 39k resistor.  Try a .01 to .033uf cap and see if it appeals to you.  
There may be insufficient space to install another pot and knob, in which case a 3-position SPDT toggle (centre off) can do the trick nicely  You can stick in a 270k fixed resistor in place of the suggested 39k and 250kpot and use the toggle to connect each of two parallel resistors.  With no parallel resistance, you have minimum depth.  With a 180k resistor in parallel, you have medium depth, and with a 56k resistor in parallel, you get max depth.  That may well be enough for your needs.  
If you want, you can stick in an SPST toggle (or if you have the room, stompswitch) to disable the dry signal by lifting one end of the 47k resistor.  That will score you vibrato.  If you need it, you can wire up a DPDT stompswitch or toggle such that when the vibrato function is engaged, an LED indicator comes on to indicate effect status.

[ESPm2M]

Mark that is some great info, thanks!  I will be modding the bejesus out of my Phase 90 this holiday season.  In another thread I asked about the sycronizing of an auto-panner and a univibe, can you suggest how I might physically do this with a P90 (I'm sure it would take a similar approach, I'm just unsure of the actual circuit)?

I will let you know how this all turns out. Eventually I will take pictures of it and all the other effects I have built since having started with all of this in July ...

[ESPm2M]

[edit - accidental double post]

[Mark Hammer]

Mark that is some great info, thanks!  I will be modding the bejesus out of my Phase 90 this holiday season.  In another thread I asked about the sycronizing of an auto-panner and a univibe, can you suggest how I might physically do this with a P90 (I'm sure it would take a similar approach, I'm just unsure of the actual circuit)?

I will let you know how this all turns out. Eventually I will take pictures of it and all the other effects I have built since having started with all of this in July ...

You're welcome.

Syncing an autopanner and Univibe may not be the wisest strategy.   Consider...

Autopanners tend to perceptually override everything else.  In other words, when it's louder on one side than the other, and which side is louder keeps changing, what you tend to hear most is the FACT that it's louder.  You can certainly tell there is another effect going on, but it recedes into the background, much like the less attractive high school friend that the supermodel brings to the party (I remember there was SOMEONE there, but...I don't think I could pick her out in a police lineup).  You can improve this by reducing the intensity of the panning (i.e., less channel to channel volume difference).

Syncing an effect sweep and autopan has the unfortunate effect of NEVER allowing a certain portion of the effect sweep to appear on the other channel.  So the sweep zone where the notches are lower down in the spectrum will always be on the right while higher-placed notches will always be on the left.  If you thought the perpetual up-and-down of a phaser was boring and limiting, try syncing volume and phasing.

In contrast asynchronous modulation of volume and phasing is far more interesting because it provides a more complex sweep and is less predictable.   If Univibe tone is what you like, it will also sound more "watery" than synced sweep.  Finally, though two separate LFOs might be a more complicated build and more costly, there is infinitely more room for experimentation and "happy accidents" with independently adjustable LFOs than with a single set of controls.

There is a thread regarding the old Ibanez Flying Pan here, somewhere around 2 months ago.  The FP is, like the P90 a standard 4-stage FET-based phaser.  The added feature is that the unit has autopanning, but has separate sweep speed for both phasing and autopanning.