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Re: MXR phase 45

6/9/1998 1:48 AM
Preben Hansen
Re: MXR phase 45
I think YES.  
You can add extra stages. That's how the P90 is made. The OB-1 PHASOR has 6 equal stages. Try to build the OB-1, and make some experiments with number of stages, and where to connect the feedback/regeneration pot.  
Ithink you could find "your tone".  
6/9/1998 6:26 AM
Yes, but...  
A bit part of the value of the small-box MXR effects is the small package. It's a tight box, and getting more stuff into it and making it reliable is hard *mechanically* not electrically. IMHO, adding stages to the 45 is almost as difficult as remaking an entire 90 board.  
There is one electrical difficulty as well. The 45 and the 90 both use a matched set of JFETs as the phase elements, two in the 45 and four in the 90. One of the hardest things to do is get matched sets of JFETs. They have to be matched for channel resistance as well as threshold voltage; this is one reason I haven't put together a 90-clone package already; it's hard to describe how to do the matching procedure, and you have to buy many JFETs to have a good probability of getting a matched set.  
There are a couple of phasers, the EH Bad Stone and the Ampeg Phazzer, that use the monolithic (and presumably matched by default) N-channel FETS in a CMOS chip for the phase elements. You get six possible FETS in the common 4049 and/or 4069 packages that are used in the EH and Ampeg respectively, so they are both six-stage.
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6/12/1998 2:47 AM
Preben Hansen
Some questions:  
How is the number of stages defined i a phaser?  
If it is true, that MXR45 is a 2-stage phaser, it has 2 FET's for varying the phase, THEN the Bad Stone MUST be a 5- stage phasor.  
The schem. for the Bad Stone that I know of, is hand drawn by N.P. and has page number 63.  
The chip with the letter E must be the 4049. All the inputs,(3-5-7-9-11-14) are tied together,and connected to Vdd(1).  
These again is tied to pin 13 and 16, why??  
13 and 16 are not connected !  
Is there a clearer schem for the BS? Some values are hard to read.  
Is there a schem for the Ampeg Phazzer? I would like to see that.  
Regards Preben
6/13/1998 11:52 AM
>How is the number of stages defined i a >phaser?  
My personal definition is that one stage is one amplifying stage with the associated RC and variable R that makes the shift.  
>If it is true that MXR45 is a 2-stage >phaser, it has 2 FET's for varying the  
Yes, this is true, by my personal definition anyway.  
>THEN the Bad Stone MUST be a 5- stage >phasor.  
I think it's six.  
>The schem. for the Bad Stone that I know of, >is hand drawn by N.P. and has  
>page number 63.  
>The chip with the letter E must be the 4049. >All the inputs,(3-5-7-9-11-14)  
>are tied together,and connected to Vdd(1).  
>These again is tied to pin 13 and 16, why??  
The 4049 is being used as six Nchannel MOSfets by tying all the Pchannel devices to ground, using the outputs as the variable resistance ports, and the ground terminal as the common source connection. The inputs are all tied together to drive the gates with the LFO signal to vary the channel resistance of the N channel fets from the output (drains) to the nominal ground pin (all of the source of the N channel devices).  
>Is there a clearer schem for the BS? Some >values are hard to read.  
Mine's very hard to read as well.  
>Is there a schem for the Ampeg Phazzer? I >would like to see that.  
Me too.
6/15/1998 12:34 AM
Preben Hansen
Hi R.G.  
About definitions of stages in a Phasor.  
I agree wit your definition!  
But I still think the Bad Stone is a 5-stage phasor. "Fet No6, pin 14 and 15, are not connected to the RC gain stage, it looks like it is a part of the LFO.  
About pin 13 and 16 of the 4049. In the Philips data sheet they are n.c. !!  
Does other brands of 4049 use these pins ?  
If so, do you know for what ?  
Regards Preben
6/15/1998 12:37 AM
Preben Hansen
Oh--- i forgot one thing.  
Do you know what types the op-amps are:  
A1-A2, B1-B2, C1-C2, D1-D2  
Regards Preben
6/14/1998 9:36 PM
Jack Orman

I have a fairly good copy of that schematic but unfortunately it is on blue paper and doesn't scan very well. If you will let me know which components you have questions about, I'll see if I can tell you what they are. Also, I have one of the original units and I can always trace the board if a component is in question.  
regards, Jack
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