Phase90 w/Easyvibe caps....

[Bucksears]

In an effort to try and save a little board real estate, I'm thinking about moving to a smaller vibe pedal. I have an Easyvibe in a 1590BB right now, but it's a little large.
I have some Phase 90 PNP Blue layouts that I could build another one, but was wondering HOW CLOSE a Phase 90 with Easyvibe cap values might get to an actual Easyvibe?

I mean, I know it's not the same thing and they are two different circuits, but would an EV-capped Phase 90 be able to cop most of the sound?

Thanks,
Buck

[R.G.]

I have some Phase 90 PNP Blue layouts that I could build another one, but was wondering HOW CLOSE a Phase 90 with Easyvibe cap values might get to an actual Easyvibe?

I mean, I know it's not the same thing and they are two different circuits, but would an EV-capped Phase 90 be able to cop most of the sound?

Uh, sure. It's 73.6% close, as measured in seconds left to play, and the sound is 43% whiter. Oh, yeah. It has 15% fewer cavities.

Whose ears, whose guitar, whose amp?

The only good way to answer this is to try it. You'll get reports ranging from "Oh, dude, it cops it 100%!" to "Man, I wouldn't scrape the bottom of my shoes with that."

[Bucksears]

Sorry, guess I should have asked 'Has anyone tried this, and how did it turn out?'

[Mark Hammer]

1) The sweep of LDRs will be a little different than that of JFETs, so there may be some nuances different between the two that you find disappointing in the modded P90...or not.  Just keep in mind that the difference between a Uni-Vibe and phaser is not just the cap values.

2) The speeds which are of use in phasing are not all useful when it comes to vibing.  This would seem to be because there are no obvious notches in a vibe, but really more like broad dips.  Those dips are barely detectable at the slow speeds which, with some regeneration, are thoroughly capable of providing nice sweep in phasers with more defined notches.  This means that the range of resistances a stock P90 uses to determine speed are way in excess of what is useful for vibing.  So a 100k is probably more useful than the stock 500k, since the "usable speed" range will be spread over more degrees of rotation.

3) Regeneration plays NO role in vibing, which is why you'll never see a Feedback or Regen control on a vibe unit.  If anything, regeneration impairs sound quality.  So you'll need to eliminate any feedback path if you want to complete the adaptation.

Certainly, the cap-value changeover is the most invasive and noticeable change to be made, but do not expect that simply swapping cap values will yield delicious chewey Trower-tone.

[shadowmaster]

I did the vibe mod (switchable between stock and vibe cap values) on my Phase 90 clone.

The result was not totally pleasing at all.

[B Tremblay]

You can try a Tri-Vibe and build it in either a 1590A or 1590B, thanks to the layouts provided by this community:
http://www.diystompboxes.com/smfforum/index.php?topic=81099.msg686675#msg686675
http://www.diystompboxes.com/smfforum/index.php?topic=81099.msg724358#msg724358

[Mark Hammer]

I did the vibe mod (switchable between stock and vibe cap values) on my Phase 90 clone.

The result was not totally pleasing at all.

The stock P90 has some regeneration/feedback via a single fixed resistor - the "famous" R28.  You need to remove or disable that path for a phaser-to-vibe conversion to work satisfactorily.  Did you leave it in or take it out?

[shadowmaster]

I did the vibe mod (switchable between stock and vibe cap values) on my Phase 90 clone.

The result was not totally pleasing at all.

The stock P90 has some regeneration/feedback via a single fixed resistor - the "famous" R28.  You need to remove or disable that path for a phaser-to-vibe conversion to work satisfactorily.  Did you leave it in or take it out?

I put a fixed resistor in series with a potentiometer for the feedback.

[Mark Hammer]

There is your problem.  Feedback....ANY amount....destroys the vibe effect.  Lift one end of any component in the feedback path and see if that improves things.  Obviously, it won't do anything about the range where the sweep is located (use the bias trimpot for that), nor can it do anything about the shape of the sweep, but it should improve the sound noticeably.

[DougH]

When I built a phase 90 I had it on the breadboard for while. I tried the "vibe cap" thing and you can color me unimpressed. Did not sound like a "vibe", to me, at all...

IMO, if you want a vibe in a small package, get a Dano Cool Cat and call it a day.

YMMV.

[Mark Hammer]

Again, I cannot emphasize enough how much feedback/regeneration detracts from vibing.  I wonder how many other folks have done a cap change, with no other modification (including removal of feedback), and been unimpressed.

[DougH]

I left the feedback resistor off, Mark. That was the probably the first thing I did when I was tweaking the phase 90 circuit.

[Mark Hammer]

As I would have expected from you, Doug.   I'm not so sure that the many who frequent here, but who have less than your track record and experience building stuff, would know to do so.

Again, the "magic" of the Uni-Vibe is not just the cap spacing, but the sweep waveform and resultng character, and the frequency range within which the sweep occurs.

[DougH]

Again, the "magic" of the Uni-Vibe is not just the cap spacing, but the sweep waveform and resultng character, and the frequency range within which the sweep occurs.

Yes I would agree that there is more to it than just the cap tuning. But I have not analyzed it as thoroughly as you have.