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Re: MXR phase 45

6/8/1998 9:15 AM
Re: MXR phase 45
Yes, I think a lot of people would be interested in a Phase 90, least I would be interested ;-)  
6/8/1998 3:47 PM
R.G. Phaser boards
I'll try to get the P90 and maybe the SS worked up.
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6/9/1998 8:19 AM
Len's Homepage has a .PDF file describing a phase shifter that is "very" similar to the MXR Phase 90. His page is at:  
The .PDF file is located in "the old, classis SPICE Circuit Attic", which you can get to through the PSPICE Circuit Attic.
6/9/1998 4:07 PM
I'll do a compare on it.
6/9/1998 4:09 PM
Mark Hammer
Your mission, Mr. Keen, should you decide to accept it, is to work up a PC-board that will accommodate up to 8 stages of phase-shift (that should be 3 quad op-amps by my count), and a jumper arrangement that will permit the builder to install less than that if they desire. I see no reason why it wouldn't fit in a 1590BB.  
While you're at it, please identify the components whose values determine regeneration/resonance, shift/straight blend, and sweep width, for those among us who cannot do so spontaneously.
6/9/1998 5:36 PM
... so is this computer going to self destruct?...  
You're right, three quads for an 8-stage. The problem is that the space inside a BB is limited to about 2" by 3" in my favorite arrangement of the box, maybe a bit more like 1.5" by 4" in the alternate arrangement. It's tight to get three quads in that small a space with standard pin-in-hole (you didn't want surface mount, did you 8-) ?). It might be doable by standing the resistors on end. Putting the pots on the board is a possiblity, but the mechanical constraints are still hairy.  
What phasing elements did you want with that?  
(a)LDR's and LED's (mechanically difficult, also need eight LDR's at $1.60 each)  
(b)LED/LDR opto like the VT54C2? (need four at  
$5 each)  
(c)JFETs (have to be hand matched for Vth, so you have to buy a bunch to get a matched set)  
(d)LED/JFET opto like the H11F3 (Need 8 at  
$1.80 each)  
(e)Mosfets (eight at $1.50 each, probably hand matched, so expensive again)  
(f)CMOS chip MOSFETS (limited signal handling range, but otherwise cheap and easy, but hard to wire because they're all in one chip, not  
spreadable to wherever they're needed)  
(d)other? (I'm out of ideas)  
I'll see if the queue has room for more board layouts. If it won't fit in a 1590BB, would you trade off number of stages for keeping it in the 1590BB, or would you opt to put it in the 1590C size, which would allow for even more (!) stages?
6/10/1998 6:21 AM

Some Boss phasers had 12 stages :)  
I have some "alternative" phaser designs you may find interesting.  
1) From an Elektor magazine 16 stage phaser.  
In a standard 1st order all-pass filter, use a CMOS switch instead of a FET or LDR. Drive the switch with a variable duty cycle oscillator. Its effective "resistance" is proportional to the duty cycle. Pulse width must sweep. The PWM oscillator is not as complicated as one would first think. Advantages: no need to match components, no expensive or hard to find components. It would be easier to fit in a rack, however.  
2) Elektor magazine Bi-Phaser  
Two slightly different 4 stage phasers driven by independent oscillators and then mixed together. Uses FETs.  
3) Switched-Capacitor phaser  
Uses a SC chip that has two state variable filters. You wire both filters as notches, drive one with a switching frequency that is twice that of the other. Switching frequency must sweep. With just one chip and the oscillator you get a four stage phaser (two notches). The magazine where it was featured showed their prototype in a very small stomp box.  
4) All CMOS phaser  
From ETI. Everything from oscillator to amplification to variable resistance is done with CMOS inverters. I doubt it works.  
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