Clean octave-down reccs please

[Al Heeley]

I've been asked to put together a pedal for a guitarist to give a clean octave down effect.
I've had a look at the ones in the GGG projects pages but they are all octave up + distortion type fx.
Can anyone reccomend a good, reasonably simple clean octave-down with pcb layout please?

[earthtonesaudio]

About the "cleanest" you'll find without going digital is the Boss OC-2, but it's not "clean" in the way that a POG or pitch shifter pedal would be.

[Al Heeley]

Aah, I'm guessing that may not be a readily-available layout in the public domain for DIY then?

[Mark Hammer]

There ARE none in the analog domain.  There are some which come closer, by virtue of filtering, but the basic constraint is that they all use a flip flop, whether CMOS or discrete, to provide a perfect divide-by-two function, and what gets generated out of that is always a square wave.  What gets done with the square wave often makes up for the apparent difference.

The Boss OC-2 and some others use the generated square wave to modulate the actual audio signal, which tends to sound cleaner.  Most others will use the generated square wave as actual audio signal.  The degree of raspiness that has will depend on any lowpass filtering applied to make it sound smoother.

[Scruffie]

What about the EHX Octave multiplexer, that might be doable http://topopiccione.atspace.com/PJ19EHOctaveMultiplexer.html
Not entirely clean but pretty good, probably the best you'd get.

[Mark Hammer]

This is one of the category that use a JFET (Q1 in this case) to essentially modulate the audio signal at the octave-down frequency.

[R.G.]

Craig Anderton's Roctave Divider, available through PAIA, is the best octave down I've heard.

But as Mark notes, it is divider based and not clean in the engineering sense. It just has good and adjustable filtering and careful design.

[Mark Hammer]

And there is actually no reason why the filtering could not be further improved upon from the basic design to make for a smoother octave sound..

[Al Heeley]

Thanks guys, I have an original copy of Anderton's famous book my parents found in a car boot sale a few years ago, not looked thru it in ages.
I'll look into building myself a roctave, though the guy interested in the pedal initially wanted an overdrive/boost/octave down all in one, seems crazy to have to clean up all that signal if he's going to overdrive it again. I need to get him to define the project requirements more closely first to see exactly how clean he wants it to go. May be a lot simpler going for one of the octave-fuzz type pedals though i think most of those are octave up?

[Mark Hammer]

The Rocktave does include a "fuzz" channel which can be blended in with clean and octave-down.  Nothing particularly special as distortions go, but it's in there.

A lot of folks don't understand octave units particularly well, overestimating what they can do.  In the case of your friend, he may wish to have the capacity to blend octave-down tone with fuzz for chords.  Silly boy.  octave-dividers don't DO chords.  They require one note at a time to work.  If your friend wants the sort of fuzz that lets him play chords, I offer the New jersey recommendation: fuggedaboudit.

In the case of octave-up, they work via a different set of principls, and while the results are not all that pretty, you CAN play a chord through them without confusing the circuitry (even though the result may confuse the listener).

Now, because of where it occurs in the circuit, and the general nature of the circuit, the fuzz sound actually CAN render chords in the Rocktave, but you have to completely shut off the output from the octave-division circuitry to do so.  You could conceivably build your friend a Rocktave with added footswitches to defeat the octave/suboctave sounds for the purpose of playing chords.