# NPD: Clean Octave Blend Clone



## NorlinNorm (Dec 31, 2016)

Just finished noodling with my newest Pedal acquisition "Clean Octave Blend" basically an Octave Up Fuzz.
Just love this pedal especially in the 12th fret & upper range of the fret board..if anyone is interested contact [email protected]


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## mhammer (Nov 30, 2007)

Is that the Prescription Electronics pedal?

I recently made myself yet another Foxx Tone Machine clone, and decided to change the type of diodes used to produce the octave. The FTM is my favorite octave-up unit, chiefly because of how robust the octave is. But where one would normally need to be well above the 7th fret to hear octaves, this thing can now produce them below the 5th fret. Impressed the heck out of me.

Of course, very few, if any, of the analog octave-up pedals produce a "clean" octave, since the method used to produce the doubled frequency itself produces at least a little crossover distortion. It's also the case that many use a pair of clipping diodes to produce a simple compression that creates the illusion of the octave lasting longer. That also tends to yield a dirtier output, although there are ways to reduce that aspect.

Note as well that ALL analog octave-up units will produce a quasi ring-modulator tone if you do double bends. That's why the Dan Armstrong "Green Ringer" - a barebones octave-up unit - was called the Green Ringer.


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## NorlinNorm (Dec 31, 2016)

mhammer said:


> Is that the Prescription Electronics pedal?
> 
> I recently made myself yet another Foxx Tone Machine clone, and decided to change the type of diodes used to produce the octave. The FTM is my favorite octave-up unit, chiefly because of how robust the octave is. But where one would normally need to be well above the 7th fret to hear octaves, this thing can now produce them below the 5th fret. Impressed the heck out of me.
> 
> ...


Hammer,
A fantastic summary, I will be picking your brain about pedal...haha
Definitely, have you down on the short list for future pedals!!!!


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## mhammer (Nov 30, 2007)

The clipping diodes I note, that can be found in the Foxx, the Univox Superfuzz, Honey Fuzz, Ace-Tone FM-2, and the Fender Blender, among many others, seem to be there to compensate for the dynamic aspects of the guitar signal, and only have incidental effects on the tone. I'll explain.

Keep in mind that plucked guitar strings have a strong initial peak, and then quickly decline, leaving mostly fundamental and lower-order harmonics as the string continues to vibrate. If one compresses the signal before the octave-unit, then the signal level is held pretty steady., but it still isn't optimal for the octave unit. That initial peak has tones of harmonic content, and when it all gets doubled, the octave gets lost amidst all that additional high-frequency stuff. It's really only after the initial transient peak that the string settles down, and the electronically-produced octave doubling becomes more obvious. Regular users of octave-up units will know that the most robust octaving is produced by using the neck pickup and turning the guitar tone way down. Why? because that reduces the extraneous harmonic content that obscures the octaving at the start of the note. Frankly, I'm surprised that more octave-up units don't include some sort of variable filtering to improve the quality of the octaving, so that a person could be playing clean and bright, step on a switch and have optimized octaving via a "prepared" signal feeding the octave.

So, the diode pair that_ looks_ like it is intended to produce fuzz (and does to a certain extent), seems to really be there to keep the level more or less "clamped". As the unprocessed string starts to die out, the octave becomes more audible, but the diode pair allows it to seem to "bloom". A buddy in St. Lazare has found that a small value resistor in series with those diodes can keep the constant-level effect of the diodes while reducing any undesired fuzzing effects. I've tried it out and he's right.


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## tonewoody (Mar 29, 2017)

Is this a Prescription Electronics COB (Clean Octave Blend) clone?

Somehow I imagined the PE COB to be an analog octave up (ie: clean-ish but not 'perfect-ish' (haha) like a POG.


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## NorlinNorm (Dec 31, 2016)

tonewoody said:


> Is this a Prescription Electronics COB (Clean Octave Blend) clone?
> 
> Somehow I imagined the PE COB to be an analog octave up (ie: clean-ish but not 'perfect-ish' (haha) like a POG.



Yes this COB Clone is a Prescription Electronics Trace!


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## mhammer (Nov 30, 2007)

The COB is an interesting circuit, albeit a bit of a misnomer. The octave itself is not "clean". However, the Blend control allows one to combine a clean signal with differing amounts of octave fuzz, where most other octave-up units confine one to either octave-doubling all the time, or octave/no-octave.

Here's a mod that might be worth exploring. The "clean" signal is full bandwidth, which means that it has all the harmonics of the original signal. The octave can be made to sound more obvious by filtering out the highs from the clean signal. So I will suggest the following:

1) in the "clean" path leading up to the clean side of the 250k Blend pot, insert a 10k and 4k7 fixed resistor in series, with the 4k7 tied to the clean side of the blend pot. This will reduce the maximum amplitude of the clean signal, but not so uo'd notice. After all, a 10% deviation from niminal value on the Blend pot is 25k, and what I'm proposing is only 14.7k.

2) Run a wire from the junction of the 10k and 4k7 resistors to the common of a SPDT on-off-on 3-position toggle switch.

3) To the ouside lugs of the toggle, connect a .01uf and .027uf cap, whose "free" leads are connected to ground. When the toggle is set to the middle position, the caps have no effect. When the toggle is set to the side positions, you'll have treble rolloffs on the clean signal alone, that begin around 1.6khz, and around 590hz, respectively, for the .01uf and .027uf caps. This will dull the clean signal so that the octave side will be contributing the harmonic content. This will not only allow the octave to be a little more obvious, but will also mean the Blend control can act a bit like a treble control. It also means you can introduce some clean bass into the octaved sound without having the treble content of the clean side obscure the octave-fuzz sound.

Because this is simply a 6db/oct filter, the treble rolloff will be gentle/modest, even though the corner frequencies seem low, and some clean treble will still come through, just not nearly as much. Raising the value of either cap will shift the rolloff point lower, and making the values smaller will move the rolloff point upwards. The nice thing is that the filter is easily defeated with the toggle.

One thing that is missing here is the diode clipping pair near the output found on a number of other much-liked octave units. As I noted in an earlier post, those diodes form a crude compression circuit that allows for the output signal level to be held fairly constant, such that the doubling of the fundamental seems to bloom as the note is held. Without that simple "clamping" of the output level, the octave may seem to fade out very soon after picking. Never having played with a COB or the COB circuit, I can't say if that would improve or degrade the normal sound of it.

FInally, consider swapping the silicon diodes in the circuit for Schottky type. BAT4x or 1N5817 should do just fine. That will make it easier to get octave doubling on lower frets, not just the stuff above the 7th.


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## Hear Ye Music (Dec 19, 2012)

I have a PE COB. Probably my favorite octavia-type pedal. I understand this circuit is different from an Octavia. The high octave sounds clean and prominent, and tracks very well. I prefer this over the fuzzy, spitty, and unpredictable Octavia sound.


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## mhammer (Nov 30, 2007)

The octave-generating part is almost a dead ringer for the octave-generating section in the Foxx Tone Machine, which also has a nice dependable and prominent octave. Prescription Electronics also made the Experience pedal, which was also derived from the Tone Machine.


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## fretzel (Aug 8, 2014)

I am sure you all know but rolling of your volume and using the neck pick up enhances the effect.


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