MXR Phase 90 LFO ?

[Pablo1234]

I Just bought a phase 90 new. The lfo sweep seams odd it ramps up then down then their is this small up down and up again. is this normal for this peddle?

[Earthscum]

Look on the inside, there should be a trimmer to adjust that. It is labeled as the "bias" in the Phase 90 schematics.
I have a KMD Phaser that I can get to do a beautiful double-lope with by adjusting the trimmer. One way will make the second lope bigger, and the other will get you into the single sweep range. From the sounds of it, you shouldn't need to turn one way or the other by very much to get that sweet spot.

[Pablo1234]

Ahh thanks that worked perfectly.

[charmonder]

neat i never new this, what is happening technically?

[Earthscum]

I think when the signal sweeps high enough it starts to flip over the action of the JFets, basically the signal starts to invert once it goes above or below a certain point. In mine, the signal inverts because the transistor base gets pulled high enough that the unbuffered LFO signal starts to bleed through the base and raise the Collector output (in a gist). Mine is a slight bit different, but they both essentially work the same way. Mine feeds current to a pin on an OTA, while the Phase 90 changes a bank of JFets' apparent resistances.

[Pablo1234]

I loved my small stone, but this phase 90 is sooo much quieter, I think I'm gonna add a pot to R28 to drag down the resonance though. I like some resonance but not a lot, Anyone know what a good resistance would be? I'm thinking adding a 100K pot in series with the 22K resistor would be more than enough to sound more like the script or Eddie Van Halen with some control.

[Fender3D]

...I'm thinking adding a 100K pot in series with the 22K resistor would be more than enough to sound more like the script or Eddie Van Halen with some control.

Sadly not... At least in my clones
Any feedback resistor will provide a resonance, you'll notice it when you finally pull off the damn resistor... (its name IS NOT R28) 

[Pablo1234]

In my block phase 90 it is R28, I lifted it earlier today and it dropped the resonance, I also added a switch and a trim pot in the batery area at 250K, when its maxed its 272K ohms and just a slight resonance but your are right if you want no resonance you would have to lift it or use a 1Meg pot or bigger. I like the lifted and I also like it with around 150 ohms resistance its not as resonant but still adds some sparkle to the swirl.

[Fender3D]

In my block phase 90 it is R28....

In your P90 has someone wrote R28 anywhere?
Or you're parroting "R28" 'cause you've read it elsewhere?

[Pablo1234]

And what makes you think its not called R28? What makes you think I am parroting what I may have seen on the internet?

[Earthscum]

in Pablo's defense:

http://www.erikhansen.net/mxrphase90mods.php
"Some time around when the EVH Phase 90 was brought to market, the orange reissue block Phase 90′s (with the exception of the Script logo models) began being built using SMT components. This makes modifications a little tricky. From what I have seen, the component numbers are not the same as earlier conventional component models. This means that R28 on a SMT board is not the same R28 on a non-SMT board. That being said, these mods apply only to the non-SMT component models. At some point, the block Phase 90′s started being built again with through-hole components so be sure to check yours before performing any mods."


And, from the same link (This may be why he's thinking you're 'parroting')

"The first, and most common mod, is to remove the feedback resistor, R28 (24K). This will make it sound somewhat like the classic script version and pretty much eliminate the distorted mid-boost. If this is not enough, then remove C11 and C12, this mod will remove the pre and de-emphasis (noise filtering)."

Also, as you can see HERE, R28 is not a feedback resistor in a 92 version, so yeah... what was that all about? Pablo, probably just easier to call it a "resonance feedback resistor"...

[Pablo1234]

 

[charmonder]

There are so many versions, there's even a line of classic mxr (dynacomp phase 90 , DIST + etc) made by Dunlop that doesn't have pcb mounted parts. http://www.phpbbserver.com/phpbb/viewtopic.php?t=185&mforum=stompboxalchemy

[DavenPaget]

There are so many versions, there's even a line of classic mxr (dynacomp phase 90 , DIST + etc) made by Dunlop that doesn't have pcb mounted parts. http://www._________.com/phpbb/viewtopic.php?t=185&mforum=stompboxalchemy

http://tinyurl.com/7s2cgk7