2 stage Ross/Ropez Phaser?

[bluesdevil]

I know the thing to usually do is add more stages to the Ropez build, but has anyone tried bypassing the first two stages for a 2 stage phaser ala MXR Phase 45?

[Mark Hammer]

I tried bypassing it just to see what two stages of vibrato would sound like, compared to 4, but that's about it.

[bluesdevil]

Thanks for sharing all your experience with this phaser, Mark! I can't believe it's taken me this long to finally build it up..... have done multiple Bad Stones, Phase 45's and a Phase 90, but not this one.
I'll give it a shot and report back if the 2 stages sounds good.
For my Ross/Ropez build I plan on using a 3pdt toggle to activate the "Filter mod" and vibrato at the same time and a separate toggle to switch between 2 and 4 stages. Also may put in a volume control.
I'll have to experiment with filter mod caps, since I read in a previous post that smaller values may sound better.
      Upward and onward!

[candidate]

I do not experience a perceived volume loss in the Ropez.  The small stone on the other hand...

[bluesdevil]

Yeah, I ended up needing a boost in volume so switched out the 15k gain loop resistor for a 33k which gave quite a bit more volume. I wanted some control over it so I tried the 100k pot + inline 47k resistor in place of the 150k output to ground resistor, but doesn't work. Maybe I misunderstood what I've read previously about the volume pot mod? I wired it as a variable resistor, should it be wired as a regular voltage divider output control?
     Also I didn't car for the vibrato in this thing and actually just did the filter mod on a switch with .0022uf caps with no vibrato..... lighter sounding  alternative to stock. Used a 3pdt toggle to switch the last 2 stage caps from stock .0033uf to .0022uf and none at all.
  Didn't bother with bypassing first 2 stages, 'cause knocking out stage 3 and 4 caps gave me the sound that was close enough.

[bluesdevil]

Okay, I went ahead rigged up the volume control as a regular output divider with the 47k in series with lug 1 going to ground.... that works.
Nice phaser, especially if you muck about with the caps in the last 2 stages. Gonna box it up now!!

[Mark Hammer]

I borrowed the circuit changes from the 1st issue Small Stone that uses a pair of OTAs for the modulation (as does the Ross, albeit with a 13600 rather than a pair of 3094s), and implemented them on a 4-stage Ross/Ropez last week.

Here is the circuit in question:


The Ross has a 270k/100k voltage divider feeding pin 3 on the 13600, just like the 270k/100k divider feeding pin 3 on the 3094 (pin numbering is mere coincidence), and a 270k resistor between pin 1 and V+.  The Small Stone had a similar resistance serving the same function, with 180k+100k going from pin 5 to V+.  The SS "Color" switch would do four things at once, modify the amount of feedback/resonance, change the sweep width, change the range of speeds, and change the LFO waveform.  VERY clever.  As you are well aware, one generally reduces sweep width as sweep rate is increased.  For this circuit, as well, a "hypertriangular" LFO sweep works well for very slow speeds, but sounds jerky for faster sweeps.  So, since the switch bops between a faster and slower range, it also compensates for optimal sweep width and sweep waveform, suitable for the rate.

The three  changes were accomplished by half the DPDT switch (i.e., a SPDT) with one small deft move: change the point where those resistors connect to V+ from the junction of the 180k and 100k resistors, to the junction of that same 100k resistor and 270k.

So far, so good.  On mine, I found that I could push the sweep width a little farther than stock by reducing the 10k current-limiting resistor coming from the LFO down to 9k1.  Do so, and you'll find a sweep that goes noticeably higher up.  Personally, I find it reminiscent of the phaser sweep in the old ELO tune "Strange Magic".  While fine for very slow sweeps, especially using a hypertriangular waveform, it sucks for bubbly sweeps.  

So here is what I did.  I replaced the stock 10k (modded 9k1) current-limiting resistor with a 12k unit.  I used a DPDT toggle to go between "wide" and "narrow" sweeps (and slower/faster ranges).  One set of contacts accomplished the V+ move outlined above, and the other set switched a 39k resistor in parallel with the 12k for slow/wide mode.  I fished around in the parts bin for resistors that were just a little lower than their stated range, so that paralleling them gave me just the teensiest bit under 9k1.

The slower range now sweeps much higher AND lower than the faster range.  Flick the toggle from wide to narrow and you can get a gorgeous bubbly fake Leslie sound that has just the right amount of sweep.  Adding a 47uf cap to ground, like the 50uf unit shown in the old SS drawing, also helps to optimize the sweep for faster modulation, while leaving slower sweeps unaltered.

Now, how all of this sounds for a 2-stager is something I leave up to you, but it will improve the usability of any 4 stage unit.

[bluesdevil]

Thanks for the info on your sweep mod switch...... I'm very tempted to crack mine open and experiment with this. That might really put the cherry on top for me.
Very nice, easy to build phaser indeed!!