MXR Phase 90 R22 mod...help

[fenderislife]

Hi guys, i'm from italy.i've read lots of times posts from this forum and this is my first post. Excuse me for my english.
I've just bought a used Phase 90 (55 euro). I opened it, and i discovered that a guy who owned it before the one who sold it to me changed the transistors: now it has 4x N5952: 3 of them look the same, the fourth (Q5) has the letters printed on it in another character. Does anyone know what transistors did it pretend to mount originally since i read that these ones are the one who work fine (on tonepad'sproject at least). I also read that these transistors need to be "matched" to work fine. How can i verify it?
Another question: he also changed the value to R22. Now it mounts a 2.2M resistor. I'd like to know how these mods affec the sound since i haven't found them on the net. I also noticed that my phase 90 doesn't have the usual "boss-like" DC-jack, and it has an inverse polaity (+ in the center).
Can you guys help me in identifiyng these mods?
Thanx in advance
Andrea 

[fenderislife]

...nobody? please....   

[Mark Hammer]

The N5952 are the "correct" transistors for this.  When they are matched, they are matched for electronic properties.  So, it is possible they are all perfectly matched but the 4th one was from a different batch.  If they are NOT matched, this will show up as a weakening of the effect at either the top end of the sweep or the bottom end.  The "matching" is just to make sure all 4 stages sweep together at the same time.  If one or more stages "give up" too early while the others are still going then the effect gets weaker.

I do not know which "R22" you are referring to.  Which schematic are you using?

Having the "+" contact on the outside, instead of the inside, is important when the plug is supposed to switch the battery off.  Unless this is a very unusual jack, it is possible the plug is wired wrong.  The adapter may work, but the plug might not be disconnecting the battery when the plug is inserted.  I think we would need to see what kind of jack it is to understand.

[fenderislife]

Hi Mark - thanx for answering.
Since i don't know how to post images here, you can see these:

http://aronnelson.com/gallery/albums/Schematics-etc/MXR_Phase_90.gif
The first image represents the schematic of my stompbox. Here it's indicated a value of 2M1 for R22, similar to my 2M2, but the original has 3M3; i'm pretty sure; you can look at this too, though it's indicated as the script version (no R28 here):  http://aronnelson.com/gallery/albums/Schematics-etc/MXR_Phase_90_Script.gif

http://aronnelson.com/gallery/albums/Schematics-etc/MXR_Phase_90_board.sized.gif
The second image looks identic to my stompbox's inside, except for this: the resistors on mine are colourated in gray, not in blue (the changed one is blue) and C8 is not elecrtolytic (all stock).

As you can see, R22 in origin was 3M3, on my pedal it has been changed to 2M2. How can this affect the sound?
For what regards the transistors there's no weakening when the pot is "all up" or "all down" so i think everything works fine. The guy who sold me the pedal said the changes were made to have a "script" phase 90. As far as i know, the "script mod" asks for changing R28 and some capacitors, but not R22. I'm just wondering why did he change the transistors too, if the stock values are the same. What do you think about it?
About the DC plug: i guess it's stock. I'm writing you what Dunlop wrote on a sticker placed under the stompbox: "NOTICE: This unit is shipped without a battery. Remove the bottom cover to install a 9-volt alkaline battery. If an AC adapter is used the adapter jack requires a 3.5 mm positive tip. 9VDC AC regulated adapters with greater than 20 ma current will work. Plug polarity: -_____(o____+  DC in 9 volts. To meet original specifications use only Dunlop replacement part #ECB 02-Regulated".

THANX to everyone who will help   

[fenderislife]

any other help??? please!