Ross Phaser extra stages questions

Started by britt-stinker, October 19, 2005, 05:11:47 AM

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britt-stinker

Hey I'm thinking of building the ross phasor from tonepad with some extra stages. i'm thinking 12 stages so that would be to extra boards right? Isn't it a four stage phaser?
But how would I go about making them switchable?
Should I go with a rotary switch? If yes what kind of rotary? a 1P12T? How should it be wired?

Thanks

Mark Hammer

The switch needed depends on how you want to tap.  Since it takes 2 stages to produce a notch, the logical approach is to tap in a manner that adds notches.  That could be after 2, 4, 6, 8, 10, or 12 stages.  Quite frankly, the difference will be negligible between some of these.  In general, when one sees tap-able phasers, the taps are taken from major transition points.  So, 4 vs 8, 8 vs 12 stages.  This would imply a 3-position switch.

The routing/wiring consists of lifting the end of the 27k mixing resistor that goes to pin 9 of the 2nd LM13600 in the original schematic.  That free end now goes to the switch, which selects that same pin 9 from any of the three "clusters" of stages.  That's all you have to do to get 4, 8, or 12 stages.  Note that the path between the phase-shift stages is NOT interrupted.  They remain connected.  The switch simply "listens in" on what is happening at each of those points.

Of course the problem/choice that remains is what to do about the feedback/regen.  You can leave it where it is (tapping the regen from the last stage), or you can have it tap other points.  For the moment, I'd say leave it where it is, since the 12th stage is a valid point for acquiring the regen signal, and feeding it back to the 2nd phase shift stage will work for all tap settings.

britt-stinker

First of all, just make it clear. I wan't it to be able to switch from 4,8 or 12 stages.
I didn't really understand if I should use a rotary or somekind of toggle. As far as I know you can't get a toggle that can switch more than two ways(except for middle off). Hmm.... Now I'm wondering could a toggle switch be used? Where off is 4 stages and the two on's switches between 8 or 12 stages?

On the new scematic/layout over at tonepad is it ic 2 you mean? The one down in the left corner?

Thanks for all your help, you are really helpfull

Mark Hammer

I wish it were possible to easily do such things with toggles, because it would make it possible to install circuits like that in small boxes with less effort. 

I think there IS a way but it means obtaining a less commonly found (and more expensive) type of toggle.  This would be a 3-position DPDT toggle with the following properties.  Let's start off by calling one set of contacts 1, 2, and 4, where 2 is the middle/common, and the other set 4, 5, and 6, where 4 is the middle/common.  Flicked to one side, the 1>2 contact is made.  Flicked to the other side, the 5>6 contact is made.  Set to the middle, both the 2>3 and 4>5 contacts are made.

IF you were able to find one of these, you could connect the free end (labelled point D on the recent Tonepad Ropez layout) of the 27k resistor that feeds the phase-shifted signal to the mixer/output stage to the two center contacts/lugs (2 and 5).  Then, contact 1 goes to the 4-stage tap, contact 4 (or 3) goes to the 8-stage tap, and contact 6 goes to the 12 stage tap.  Actually, the wiring is easy, the FINDING of the switch hard...but not impossible.