I recently bought an MXR Phase 90 script logo from 1980 on Ebay...Sounds great...But there's a nasty distortion that I was not expected on this vintage stuff...Do I have to make the R28 mod as well?? Or is this another problem?
Thanks for your help!!!...

Hmmm, that's interesting. I've always thought that the R28 mod was only for the newer Dunlop RI but I could be wrong about that....

What kind of pickups are you using, are they very high output?

I was using single coils pick-up from my strat...So not a very high output...

The R28 mod is for new P90's to make them sound like the old ones.

It could be a bad connection causing the distortion. I would go over to: http://www.diystompboxes.com/forums/stompboxforum/
and post your question. There are a lot of smart guys over there that could help you out.