MXR Phase 90 reissue problem

[the_necropolitan]

Hey all,
I'm new to this board, relatively new to the modding pedals thing...So I bought an MXR Phase 90. I did a couple mods to it. I swapped out a resistor (I think it was R15...it's under the pot) to 470 ohms for a faster speed. I then did the R28 removal mod, but instead of removing C11 for the other half of the "script" mod, I replaced it with a 0.033uF metal film cap for more highs. Lastly, I swapped out the stock LED for an ultraviolet LED.

The pedal works...however, it is humming pretty bad when it's switched on, and the hum continues while I play and is as loud as the effect itself it seems. When I stop playing, the hum continues to ebb in and out at the speed of the phase. In addition, this thing entirely lost its low end and is very distorted sounding. Does anyone have any idea why this thing might be sounding so bad? My only two thoughts are that replacing C11 instead of just removing it might be simply amplifying the background noise of the pedal...or, it could be possible that the ultraviolet LED could be introducing a lot of noise into the circuit.

Thoughts? Help!

[Mark Hammer]

1) Welcome.  Congrats on the first post.

2) I think you did the right thing by starting with a mod rather than a full build. 

3) Safe to assume this is a pedal with through-hole, rather than surface mount, parts?

4) Are you certain that the parts you thought you were replacing were actually the parts you changed?  I.E., were you able to confirm that the indicated components truly conform to the schematic you were using as a reference?

[zombiwoof]

There's actually more that you can do for a more accurate Script mod.  Here's a link to the instructions that are in the Gallery here:

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/MXR_Phase_90_to_Script.gif.html?g2_imageViewsIndex=1

I did everything listed under "Script Mod", I didn't do the optional mods, and it came out well (except I'm having a problem with ticking that I've got to fix, that I think is not related to the mod itself).

So just removing R28 will get you close, but these other steps will make it even better.

Al

[Joe Hart]

instead of removing C11 for the other half of the "script" mod, I replaced it with a 0.033uF metal film cap for more highs.

Welcome to DIYstompboxes.com!

Anyway, I'm not totally familiar with the circuit (I own one and did some mods, but don't know every aspect of it!), but you do realize that you replaced a .00068uF cap with a .033uF one? That's not double or triple the value, it's almost 50 times the original value. I know in many circuits increasing a value by 50 times changes everything. Maybe try a .0047uF cap and see what happens? Hope this helps!
-Joe Hart