CA Phase Shift

[Anonymous]

Starting to build the "Phase Shifter" featured in "Craig Anderton's Electronic Projects for Musicians".

It has 4-stages (op-amp/opto-isolator stages).

Was wondering how many more stages could be added?

Thanks,

J.D.

[The Tone God]

As many stages as you like, you have the space for, and your power supply can handle.

Andrew

[Jason M.]

J.D.,

You can add as many as you like.
I added two additional phase stages and it sounds pretty good.

How many phase stages are you planning to add?

At some point, the LFO will run out of current to drive all of those optos, so you may need to buffer the LFO output. You can probably get away with a total of 8 stages with no additional current drive.

Two 9V batteries won't last long with that many stages. My 6-stage shifter eats up around +/- 15 to 20 mA. That's a total of 40 mA! So plan on building a power supply.

When you add stages, make sure to move the resonance control to the last phase stage. (details are in the archives)

This is jumping ahead, but one thing you may consider building is Craig Anderton's Retro Stereo. The phase shifter sounds amazing in stereo!

Good luck!
J.

[Mark Hammer]

Jason's comments are bang on.  There ARE limits to how many LEDs the LFO can drive at once (one of the reasons why some optical phase shifters use those two-LDRs-off-one-LED units).  Certainly adding more will increase both current consumption AND the need for more current drive.

Also the Retro-stereo (or some equivalent method) of producing two different phase-shift sounds is pretty cool.  If I recall correctly, one of the CA phase-shifter designs (from the book not the GP article) has an add/subtract switch option already.  Several things to remember about the add-subtract method: a) running both in stereo can cancel the notches acoustically (add a peak and anotch and you get nothing), b) there are level differences produced by adding peaks as opposed to carving notches, c) feedback sounds great with one and appalling with the other.

I have a DOD FX20 phase shifter.  It is LM13600-based, similar to the Small Stone and Ross units, but has 6 stages and "stereo" outs (one for add, one for subtract).  Experiments with that one confirms all the assertions made above.

[LP Hovercraft]

They sure don't design them that versatile anymore.  I built one modded for 8 with a 4/6/8 switch.  6 stages has this killer deep whoosh but  8 stages sounded a lot like the Boss PS-2 (which I dont like).  If you want to mod on extra stages, keep in mind that the envelope controlled ps option was made for four stages and did not work at all to drive 8 LEDs on my bench.
Ultimately, I decided that the four stager with envelope control was the bees knees because one can squeeze a lot of groovy vintage sounds out of it.  I love the way it sounds with fuzz!  It is quite nice in a "univibe" range as well.  Good luck and tell us how it goes!

[Anonymous]

Thanks to everyone that responded to my post.

Gave me alot to think about - and some things to watch out for.

Decided to stick with 4-stages just as the original schematic calls for, since I'm going to be driving it with the Envelope Follower (proj. #25).

Just ordered the parts for a 12-stage phase shifter (schematic shows 8-stages) using Vactec Vactrol 5C4/2 (dual-element Opto-Isolators). Is voltage controlled with a buffer before Vactrol LED's. Also has a built in LFO (can choose between internal LFO & external voltage control).

Will post on progress of these to projects.

[Mark Hammer]

Note that they don't all have to be SWEPT phase shift stages.  The MXR Phase 100 has 4 fixed and 6 swept stages.  At the end, its really all about cumulative phase shift  What the swept stages contribute is added to what the fixed stages are already providing.  Very very cheap simple way to increase effect intensity.  Doesn't require matching of anything.  No distortion either.  As close as it gets to "something for nothing".

[Vsat]

Think I'm going to keep quiet about this one...
Mike  

[puretube]

TZP?

[Vsat]

TFSP!