Oberheim P-100 Phasor. Schematic?

[frequencycentral]

I suspect it's the same as the Maestro MPS-2 Mini-Phase:



...but I want to be sure!

[richon]

i smell another "phaser" in the oven???

[frequencycentral]

i smell another "phaser" in the oven???

Well, err, maybe! 

[Slade]

Okay, I'll try those 100k resistors!!!

[frequencycentral]

Okay, I'll try those 100k resistors!!!

Who you been talkin to? You should try 'infinite' resistance too.

[TELEFUNKON]

some pictures for tracing: http://www.j-guitar.com/sp/sea/data/1244/r/1367_4.jpg   http://www.loudmusicseattle.com/uploads/P-100_inside.JPG

[richon]

Okay, I'll try those 100k resistors!!!

Who you been talkin to? You should try 'infinite' resistance too.

NO RESISTOR TEST READY:

1.- almoust no phase, even not phase, only in a way a weird TREMOLO
2.-"pop" noise in a tremolo
3.-not musical tremolo/phase efect due to the UNIVIBE caps mod to the 4 stages
4.-I seems that infinite (or no resistor) paralelled to the JFET changes SO MUCH the resistance it just wont leave space for a good phase and only a tremolo kind of sound.

[Slade]

Okay, I'll try those 100k resistors!!!

Who you been talkin to? You should try 'infinite' resistance too.

^^^
With this guy.

[frequencycentral]

That's very interesting. But the Maestro MPS-2 is reported to be a good sounding phaser, so infinite resistance must be possible. Maybe it's in the nature of the FETs used, their vgs, or in the swing of the LFO. The MPS-2 LFO looks to me to have more swing than a P45 LFO, so maybe to use infinite resistance we have to use a different LFO too?

[StephenGiles]

Interesting, I think that the original EH Badstone used 2N4302 FETs, and that sounded great.

[frequencycentral]

It did indeed, with 120k resistors between D and S. If I'm reading data sheets correctly 2n4303 have higher vgs than we would usually choose for P90, P45 etc?

[richon]

my test were with 2N5458 (Vgs= 1,55V)

[frequencycentral]

I have some matched sets of 2n5485 with vgs of 2.5v, too high to work well in my P180 build - maybe they'll suit 'infinite resistance' better?

[frequencycentral]

More interesting info:

http://www.diystompboxes.com/smfforum/index.php?topic=81606.0



http://www.diystompboxes.com/smfforum/index.php?topic=60341.0

[frequencycentral]

First series of P90 didn´t have a 22k between S and D. The resistor ensures a definite phase angle even if the Fet´s should be fully off and improves the curve of the phase angle.

....so does anyone have a link to that version of the P90 schematic?