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Roto effect

Started by phatt, August 17, 2012, 10:08:06 AM

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Thought it time I posted something for folks to tinker with. This one has been sitting on my breadboard since last year.
I'm calling it the LessLee ,,cause it weighs a lot less than a real one.

I doubt it will come across as good as the real thing but it seems to do the trick.
Now just a matter of producing a board but other things taking up time.

I intend to use an old volume pedal for speed control (VR1) so if I layout my board small enough I might get the whole thing into the volume pedal housing.

The main part is the XR2206 chip which is likely capable of many options and many ideas where tried and although some produced interesting results I only needed the basic subtle rotation effect.
At slower speeds this certainly produces a very rich spacial effect different from straight chorus or phasers I've heard.

At high speed some glitching may bleed through depending how well you set it up. I made better progress by uping R4 and keeping R6 and R8 smaller.

You can of course insert other phase circuits in place of U4 and U5 but this seems to be doing a fine job and chaining more phase stages does not seem to improve the sonic result if anything they sound wonky at high speed.
I'm running this from 18VDC plugpak and testing showed it did not run well below 12VDC.

Now I just have to find time to build the darn thing. :(
Have fun with it,,Phil.

J M Fahey

Wow !!!  :o
That's a WILD application of XR2206 !!!  :duh  :loco
Congratulations  :dbtu: :dbtu:
Post some MP3


Yep I figured a sound clip might be in order so this might give some idea of the effect. ;)

Guitar> Lesslee> PhAbbZone preamp> The old faithful SS Laney Amp> DI out> Laptop.
Only edit was normalization, Then Convert to low quality MP3.
Being a DI recording it may sound a touch bright through small speakers so take that into account.

I have already been using a bod-gee maze of wires on a temporary board at our local muso club for quite some time and it really does add some magic.
I've found that with depth dialed back you can leave it on for just a touch of spacial depth to a lot of songs.

The trick of was found by accident,, long story but the XR chip does Tremolo (Volume modulation) in a different manner (which is beyond me to explain) then by simply passing that output through a phase circuit produces a sort of pitch shifted output not unlike a Leslie cabinet.

Having heard Real Leslie's on many occasions the spin effect is a reasonable approximation of same, well that is to my ears at least.
I have heard the H&K Rotasphere on Utube and it sounds pretty good but likely far more complex to build than this one.
For those in the land down under, (Australia) the XR2206 chip is in the Jaycar Cat (about $15)
opps forgot , first is Tremolo then Dry only, followed by Vibrato

J M Fahey

Congratulations !!!
:dbtu: :dbtu: :dbtu:


Nice one, Phil. Now I just might have a use for the old Cry Baby shell I've had hanging around. That seems to be the easiest way to make it ramp up and down. Paralleling the output into LP and HP filters into stereo outs might even be a way to bring it even closer. Hmmm... gotta think on that one. Good job.


Glad to hear positive comments :)

Just a couple of details that will interest anyone wanting to build this.
Different values for C6 and C7 effect the spin depth.
The large values shown on the drawing are what you hear on the clip.
These increase the effect but may sound less realistic to some ears.

I've found smaller Values may produce a more natural Leslie result.
Off course you can try anything for more extreme results and see how it sounds. :tu:

At the Mo I've opted for both C6, C7 at 22nF.

Re the pedal and speed thing;
Anyone clever enough to make the pedal Ramp up over time??
Might be interesting as the 3 meg pot in my pedal does require a steady foot to get a natural speed ramping effect.

There is a mechanical leverage issue in the pedal which by design is not exactly linear in action.
Add too that the pot is a rare 1/4 turn gizmo and is likely some funny log curve as well but it's all I had big enough and fitted into the old FV50 pedal.
I think I've just got used to using it now so I'll leave it until the pot wears out.

Oh A Flashing Led might be a nice touch but I wish to keep it fairly simple as I already have enough knobs to play with. lol.


Hummm... I've had a lot of ponders about a s.s. Leslie over the years, mainly around a four-phase oscillator controlling some amplitude and phase modulators in quadrature to get a rising pitch as the amplitude goes up (horn swinging towards) and falling pitch as the amplitude goes down (horn swinging away) and naturally gave some thought to inertia with speed change, and based on the original Leslie idea of just two speeds, so...

Applied to your circuit; how about using a FET as the Speed resistance, slug the gate with a suitable cap, and use a footswitch to select between a Fast setting pot and a Slow setting pot?  A LDR and LED might also be worth considering.
If you say theory and practice don't agree you haven't applied enough theory.


Hi Roly,
          I did ponder many ideas but was not brave enough to try the ramping so thanks for the tip. :tu:

Short story, I tried a few ideas today with a fet and cap but rather than a dedicated 2 speed switch I figured it would ramp the pedal stroke anyway.

Not sure if I'm doing it right but it is definitely *Ramping Down* quite well but Not as good at speed up.

After immediate full off pedal from full speed it takes a good 3 seconds or more to slow down but the other way is not as fluid.
but that is likely how a real motor would work anyway so as I'm yet to design the board and decide on a box I'm open to ideas.

It certainly makes the oddball pot in the pedal a lot easier to control.
Not sure if I'm doing this right but seems to work? (See drawing)

You can just hang a 10uF cap from pin 7 and leave the speed pot as is but Ramp up seems to suffer.
Seems to work better with FET in place, Only using Gate and source terminals. I've used a 2sk246 and an MPF102,, both the same result. I'll fiddle more tomorrow.
Thanks for the input :tu:


Constant current source and sinks.  ???  Take the pot position as a "DC" control level, demand into an op-amp, feedback from the (shunt) cap voltage, output controls up and down current source/sinks (which can be set independent of each other) with a deadband or reduced sensitivity (bit like introducing some controllable backlash - sounds like a 555!).
If you say theory and practice don't agree you haven't applied enough theory.


The XR2206 chip makes a good oscillator/function generator. Too bad the market didn't respond as it's no longer in manufacture :(

Seeing this design has convinced me to stock up,
Thanks so much.


Jameco still list both the chip $6.49 and a kit $27.95.  Mouser are quoting an astonishing $117ea on a stock of 2.

Given that this chip has been around almost as long as the 555, perhaps more than 30 years by my memory, and it is overwhelmingly represented if you Google "function generator", I don't think Exar have anything to complain about with market acceptance.
If you say theory and practice don't agree you haven't applied enough theory.


Well I finally realised my ramp idea using a fet was way off.
Anyway the good news is the Cap trick hung off the top of the pot does the Job.
Somewhere around 10uF seems to do the job
Hey and only one extra part,, ohh yeh I like that. :)

I was going to wedge the whole thing into the old volume pedal housing,,,till it dawned on me that there is no room for a stomp switch. I completely missed the bleeding obvious flaw in my master plan. :loco
So it looks like I'm going to go for a separate box and plug the pedal via a short lead.
Oh well :( down to the shed to find some sheet metal.

As to the availability of the XR2206, I got the impression there are plenty still around.

I think what might make this circuit appealing is it has no leds and LDR stuff to have to muck about with and hence would not be that hard for the beginner.

I recently had the chance to compare this unit to the rotary effect on my mates ME50 unit,, We both agreed the ME 50 sounded like a toy.
And having heard a few Utube clips of other circuits claiming a rotary effect I'm fairly confident this will be worth building.


Well I did actually find time to build this one in between a whole lot of other boring domestic stuff.

What drove me most was I blew up the temperory circuit which was thrown together in a mad hurry many months back and of course It had no protection diode for the DC input.

And like a complete idiot I plugged another power supply in which was reverse wired and by now you already know that fizzing caps and smoke came next.

So while madly diving for the off switch my brain was reciting a hundred times,,
why didn't you at least put a diode on the DC input you idiot. :duh

I think the Gods where trying to tell me something and where at least kind enough
to leave my XR2206 chip intact and working. phew

Some small mods to original; One being a bleed resistor across the Trem/Vibe switch as it was a bit glichy when switching and a 10uf cap across the speed control to give a ramping effect.
Also C6 C7 are 22nF and added a switched 330nF to alter the angle while in Vibe mode.
Having now used it for a while, Frankly I don't think it's worth the fuss.

I decided to affix the pedal beside the control unit so it's all in one box.
The only real drama was a dud cap which drove me on a wild goose chase far a couple of days but a good rest and a day away from it all helped.
I then picked the issue within a few minutes.  8)

The output of u2 (which should be at bias level) was latching to the full 18Volt rail because C1 was dud so no signal could get past u1 and u2 but the rest of the circuit passed signal.

The added bit is just a 9volt regulator which drives an auxiliary DC socket to power other pedals which require lower voltage. one less plug pak is always a nice idea.

Should be obvious that you don't need to use a pedal so a speed pot will be needed if you don't wish to use a pedal.

I'm Very happy with the end result.
Adding a couple of pics of the finished unit.


BTW, while scrummaging through my 2011 Jaycar catalogue I noticed that they still list the XR2206 under "computer and misc".
If you say theory and practice don't agree you haven't applied enough theory.


Still seems to be a lot of them on the bay, got 102 hits on the search running from about $2.50 to $20 each. A lot of them seem to be coming from China, so someone is still making them. Or at least branding them as such.