MXR Phase 90 Question

[Baktown]

Greetings everyone!

A friend of mine who's a professional musician asked me to build him an MXR Phase 90, but (and I paraphrase) "not the one that sucks out all the bottom end".  I've never even used a phaser, much less built one, so I need some opinions on which mod to use on the Phase 90. 

After reading some different posts, I've seen references made to the Script Logo mod.  I assume this is the original circuit?

Any suggestions or experiences anyone wants to share?

Thanks in advance.

Axl Bundy

[mac]

I'm soldering one right now. Kind of EVH version.
Look for Phase 90 at tonepad.com. You'll note a 22k resistor in red in the pdf file. Add a on/off switch and you'll be close to the EVH version I guess, off=script logo, on=block logo.

Look at this picts:
http://www.erikhansen.net/diy/p90script.jpg
http://www.erikhansen.net/diy/p90_79scriptblock.jpg

There are 12 10ks in the script version, 11 in the block version, 10 in the schem. One is in the LFO, replaced by the 4k7 in the schem, the other probably at the output as in the Ross Phaser, not sure.

mac

[Baktown]

Thanks for the info.

I'm still unsure which mod restores the bottom end tone?

Anyone know?

Thanks!

Axl

[mac]

There is a mod in new versions known as R28 mod, ie, removal of the R28 resistor. I guess this one goes one opamp before than in the tonepad schem. Not sure.
Just breadboard before building and listen to it with and without that resistor.

mac

[Mark Hammer]

"Not the one that sucks out the bottom end?"  Where the heck did that come from?

There are a few responses to this.  First, I have never heard comments here about the P90 sucking out bottom end.  It IS possible, I suppose, that a bit of low end disappears through the circuit in a way that may not show up in all rigs with all guitars, but given the amount of traffic that passes through here, multiplied by the number of years the forum has been active, you'd think that people would have mentioned it by now....and they haven't.  IF, and I repeat IF, there is any erosion of bottom end, then the simple solution is to up the value of any caps in the signal path so that whatever bass rolloff they impose in the course of blocking stray DC is shifted a little further downward.  So, increase the .01uf cap on the input and the .05uf cap on the output to .022 and .1uf respectively.  http://www.tonepad.com/getFile.asp?id=42

The second comment is that EVERY phaser sucks out the bottom end if it sweeps low enough. After all, it is intended to produce notches and a notch is a cut at a specific frequency.  So, perhaps all you really need to do is to adjust the bias of the FETs such that the phaser does not sweep down too low and cut his precious bass.

Having said all of that, my advice would be to build the Ross Phaser clone at Tonepad.  For many reasons.
a) The board will fit in a 1590B chassis (you may need to file the edges of it a bit, bt it will fit)
b) There is no matching or selection of FETs involved and you don't need to buy more LM13600 chips than you need, the way you have to buy extra 2N5952s to be able to identify a suitably-matched quartet for building the P90.
c) Though it has more parts, most are resistors, so It won't cost any more to build than a P90.
d) It has a proven track record and lends itself to a wide array of useful mods.
e) It sounds damn good.

[Baktown]

Mark,

Thanks for the info and guidance.

Rock on!

Axl

[Mark Hammer]

You're most welcome.  I'm just curious, though.  Exactly how many Buck Owens tunes have a phase shifter in them?

[Baktown]

I love it!  Someone recognizes Bakersfield as being Buck Town!

It was a sad day indeed when ole Buck passed on.  He's sorely missed by everyone around here.

Axl

[mac]

Maybe "sucks low end" is is not a good description. I read complaints about the reissue version having too much feedback (or recycle), that's why some remove the R28. I went to a music shop last week to hear a reissue and yes, it sounded quite different than the one in my breadboard without feedback. I prefer mine, more vintage.
Anyway I'll plan to put and on1/off/on2 switch to take variable feedback from the first and second stage, they sound quite different. Taking fb from the first stage sounds like the reissue.
As soon as I figure out how to put about 50 parts in a 10x5cm board I'll post picts and samples.

mac

[Baktown]

Very cool! 

BTW, the friend I'm building this for is in a UK based band called The Contrast, here's a link to their Myspace page:

http://www.myspace.com/thecontrasttheband


He plays a variety of Rickenbackers through a Vox AC30 which yields a really good retro sound.

Axl

[mac]

He plays a variety of Rickenbackers through a Vox AC30 which yields a really good retro sound.

Who needs more?

mac