vintage block logo mxr phase 90 distortion

[czech-one-2]

hi, i'm new here so this is my first post. i have a 81 mxr phase 90 [last vintage block logo] that distorts. so i removed r28,c11/c12-much better. still not clean enough for me and i have to back off the trimmer to lessen the distortion. any idea what else can be done to clean this phaser up? i'm open to suggestions
thanks for your time!      bk

[czech-one-2]

 anybody?  would socketing/changing the 3 tlo62cp ic's with more high fi ic's such as burr brown opa264ap or lm833 be helpful? change the ceramic caps to metal film? any suggestions would be awesome.

[czech-one-2]

also, how do i insert my board pics from floppy disc?  :-(

[Mark Hammer]

I would not describe them as "notorious", but TL062s are known to make a tradeoff between noise and current consumption.  If the chip is not in the signal path, or if there are other means of controlling hiss, AND you need to keep current drain low, then the TL062 is a fine choice.  If you have all the current you need, but hiss is a matter of concern, then the TL072 is a better choice, as is an LM833.

The FETs are somewhat prone to distortion.  Certainly not the weakest link, but if pushed hard enough...   One possible solution is simply to either keep the input signal level modest, or to attenuate at the input, and compensate with a bit of boost at the output.

And welcome!   Is this microphone on?  Czech....czech....czech.

[czech-one-2]

hi,thanks for the reply! [i was wondering if my question was so inane that i was being shunned by the techy types]
ok, its not hissy or noisey,so all is good there. it just distorts [breaks up a bit] and i play clean 80% of the time. i have a 2 stage dod 201 which is nice but i like the more pronounced 4 stage phase 90. i'm using very low output single coils [5.7k] and the phase 90 is first in line as the breakup gets increasingly more noticable behind any buffered pedals. im not real deep into reading schematics and ohms law so i was hoping to find someone who has experienced this with a phase 90 and has a remedy in addition to the r28/c11/c12 mod.
i've heard that mxr intentionally added some grit to achieve eddies sound without a distortion pedal.is that true?
i know most folks would say just buy a different phaser,but im almost happy with this one. i'll buy a dod 490 or 401 if anybody has one for sale but i'd really like to tweak this one. in your above response you mentioned fet's. do they wear out like ceramic caps and become noisy with age? should i replace them one at a time or is that a waste of time? i'd at least like to be taking an educated guess,not just swapping components. by the way this pedal is not collectable,it was painted by a hippy on a bad acid trip which my laquer thinner took care of nicely but he also scratched of the p in phase-haze 90?
any help would be awesome folks!

[czech-one-2]

ok,i made a discovery! i tried a 9 volt battery instead of the 1/8'' mini plug from my dc brick. NO DISTORTION!
so i believe i have narrowed it down considerabley.
my dc brick is putting out 8.8v while the battery is 9.6 volts. any idea why the battery tames the break up? whats going on here?

[petemoore]

  It could be a headroom issue.
  Perhaps the bias on the Jfets is a ratio thing associated with voltage supply.