Univibing a six stage phaser ?

[tomtom]

I'm on building a "modulation box" with filter, tremolo and phaser on the same enclosure.
The phaser section is based on the Maestro Stage Phaser, a fav of mine, with a thick phase sound and a huge sweep...I love it.
It uses six phasing stages (five moveable 3094 OTA like the Small Stone and one fixed (??)).

For better flexibility, I was thinking about some tweaks... but the fixed stage seems strange to me. The best idea lies in a switching system between a six stage like the original and a four stages with univibe range caps. With this design, my Univibe alike phase section will have three moveable stages and on fixed.

Do you guy think it may work great ?

A four/six stages switch is another easier solution maybe useless ?

A six stage with univibe alike caps ?

A four/eight stages switch ?

A six/twelve stages switch ?

I'm lost...the original sounds really good and modding it to sound a bit like a Univibe would be a nice feature...

 Thanks for any help !!

 Tom

[Mark Hammer]

In theory, a 6-stage Univibe is possible.  There are a few things to consider, though.

1) Would a 6-stager *sound* like a Univibe or is that just too much phase shift?

2) The Univibe cap values distribute the phase shift fairly evenly across the spectrum.  No reason why that could not be done with 6 caps/stages, but it may mean recalculating the values and re-sequencing what goes where.  May be best to leave 'em where they are.

3) Switching 6 caps will be problematic if done by toggle switches carrying the signal.

Would the difference between 4 and 6 stages be audible?  Not likely, especially if as you point out, the Stage Phaser has one fixed stage.  On the other hand, since you're building rather than JUST modding, you can make all 6 stages variable.

You will note that the 274A Stage Phasor takes its regen signal ("balls") from the last stage and feeds it back to the splitter/mixer stage ahead of the phase-shift sections.  In this regard, the design does easily permit you to insert the regen signal at various entry points the way one can with FET or LDR-based op-amp blocks.

One mod that is loads of fun is the Phase-filter mod (which you can hear in action at Charlie "Moosapotamus" Barth's page).  In truth, I have only ever heard and seen it in action in a 4-stage context/design.  That is more because the chips it was initially implemented in were expensive and quads, and because the designs I tried it on (Ross, Small Stone) also had only 4 stages.  A 6-stage unit with Phasefilter capability has the option of converting 4 stages to lowpass with the remaining 2 used to produce a notch, or 2 poles of lowpass and 2 notches.  Both of these would sound interesting, with the first one producing a more robust modulated wah-wah.

[tomtom]

I took my time to answer,  I have to think about it.

I want to stay with a six stages for the phaser, so maybe I may build two phase shift section, one for the six stages and one for a pseudo four stages univibe.
I read a thread about univibing a Ross Phaser, where you explain a "Balls" like resonnance control is useless for a univibe type phase shift.
I wonder if it's fine if I use the stock fixed stage for the phaser and a modified one with the right cap and a trimpot for internal Balls control for the univibe?

I already have a filter (thanks Mark for your DOD 440 mods, i'm going to try them !) and a tremolo so maybe both vibrato and phase filter mods are less usefull in my case but I would be interested with the last one, could you explain me how to do it?

You spoke about two modes (4 stages lowpass, 2 stages notch and 2 poles of low pass and 2 notches), it will sound like a modulated band pass filter ? I mean I wonder if these modes may sound like the Dod like filter already inside the box.

Thanks