Phase90 Vibrato Switch- or Cheap & Easy Stereo Phasing

[DougH]

I've got the phase90 on the breadboard right now and have been playing around with it. If you disconnect the "dry mix" signal path it will produce the queasy pitch-shift "vibrato" sound similar to the "vibrato" switch on a uni/easyvibe. Using the Tonepad schematic as a reference, this means disconnecting pin 1 of IC1a from the 150k that feeds the base of the Q5 recovery stage.

I've never had much use for the "vibrato" sound, unless I wanted to use that seasick sound for comedic effect. (The mixture of this and the dry sound is what actually produces the "phase shift" sound.) However, it occurred to me at 2am this morning that this could be used as a simple way to implement a stereo phase shift sound as well. This should work if you already have a stereo buss in your pedal chain (IOW, another pedal like a delay for example, that breaks out your signal into stereo). What you do is stick the phaser on one side of the stereo buss, and put it in "vibrato" mode. With "dry" on one channel and "wet" on the other, the phase shift sound is produced acoustically and with some physical separation, should have some spatiality. Of course, this should work with any of the 'vibe derivatives as well. I'm going to try this tonight and I expect it should work. I would think most analog phasers could be modded to produce just the vibrato signal.

When contemplating phaser projects I've thought I'd really like to implement stereo, if possible. (And I realize there are other methods as well - each signal 180 deg out of phase, etc...). But signal routing and bypass can present some challenges I didn't really want to spend time on. So with so many inexpensive and readily available stereo pedals out there today, why not just let them take care of the routing issues. Then implementing a stereo phase sound becomes fairly simple.

My apologies if this has already been covered elsewhere. I searched and didn't see this mentioned in other phase90 threads.

[DougH]

Update- I tried it last night. While it does "stereo-fy" your sound and does a nice stereo chorus approximation, it doesn't quite get the cancellation to produce the notches to do the phase shift "swoosh". So while it sounds fine, my other stereo pedals (required for doing this) can already do this sort of sound. It was a fun experiment though.

In order to get good notches I think the dry/wet signals need to be mixed within the circuit. I'm thinking a better approach to stereo would be two phase shift lines driven by a quadrature LFO or something along those lines. Sorry if this is old hat to all you phase shift folks out there. This is the first time I've dabbled with this stuff.

[tcobretti]

I'm sorry it didn't work, I thought it was a very cool idea.

[DougH]

Well, it does work if you want a pseudo stereo chorus. But if you already have a stereo buss you probably already have that.

[jlullo]

I was planning on trying this out with my Phase 90 (the vibrato mod).  Using this diagram, the correct resistor to lift would be R8, right?
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/MXR_Phase_90_board.gif.html?g2_imageViewsIndex=1

[DougH]

I'm not familiar with that layout so I can't be of much help, sorry.

[jlullo]

it's ok doug, i'll play around!  thanks for the post though!

[DougH]

Best bet is to take the tonepad schematic I mentioned and use that as a reference for finding the connection to break on your pcb layout. I don't know if I would do this to a commercial pedal though. You will probably have to cut a pcb trace to disable the feedforward from the input to output stage that mixes the dry signal with the vibrato signal.

Edit: It may just be a matter of removing the 150k mix resistor from the feedforward network.

[SteveB]

I have gotten nice results using the vibrato side of the Neovibe in conjunction with a delay. It produces nice sounds whenever the modulation signals cross each other.

A while back I tried a similar thing as you did, running a stereo delay into 2 amps. One side of the delay went into the Neovibe & amp, while the other side went striaght to the other amp. The phasing did not move across the stereo spectrum, but the overall sound was nice & spacious when using different delay settings for each side.

[DougH]

Thanks for the comments. It did sound nice and spacey, and had a "vibey" quality to it, with just the "vibrato-ed" phase 90 on one side and the dry signal on the other. It just didn't have the swoosh, and it wasn't particularly easy to get balanced.

[roseblood11]

I built the Phase 90 using the layout from tonepad.com. I added the vibrato mod as suggested by Mark Hammer (in another thread): Lifted one side of the 150k resistor (just below IC1 of the tonepad layout), and added a spst switch there. Vibrato works fine, but the switch produces a loud popping sound. What could I do?

http://www.tonepad.com/getFileInfo.asp?id=42

[Mark Hammer]

I've done it with the stereo chorus on my little Fender SK30 amp.  It provides the same wet-to-one-channel-dry-to-the-other split that the old JC120 did, and has a stereo send/receive loop.  Plugging a a slow-ish phase-shift-only signal into either channel's loop gives some really nice spaciousness.  Pity those speakers are only 8" and the voice coils are maybe 10" apart.

I still think that someone out there needs to whip up a little daughter-board with 4 fixed phase-shift stages that people can plug in wherever they want.  Those stages could be lag or leading, or both. (i.e., cap can be to ground at the non-inverting input or between that pin and the previous stage, or one way for some stages and the other way for the remainder).  A bit of fixed or swept phase-shift can introduce some interesting things.

Here's an interesting music-course site for those interested in all things notch-related and or time/space-related:  http://www.music.mcgill.ca/~gary/307/index.html#Outline