Octavio and Octave up Theory

[markphaser]

Octave circuit theory:
A Octave pedal has a phase splitter stage to produce two identical but in phase opposition signals.The phase splitter has one input and two outputs the two outputs are inverted with respect to each other. That is as one increases in a positive direction the other increases in a negative direction.The special stage which does the full wave recification (each octave up pedals does there rectification different) that takes the lower half of the wave and flips it up over the middle in the same period of time the new waveform has two peaks and two valleys or two times the frequency.

Octave pedal goals are:

1.) Preamp stage
2.) Phase splitter stage
3.) rectification stage
4.) transformer (maybe) this is used to phase split and then rectify
5.) preamp stage output

Here is a list of octave up pedal schematics::

http://www.geocities.com/j4_student/rogermayeroctavia.gif
http://www.geocities.com/CollegePark/Library/1355/octavedoubling.gif
http://www.geocities.com/j4_student/tychobrahe.gif
http://www.geocities.com/j4_student/tonemachine.gif
http://www.generalguitargadgets.com/diagrams/scrambler_sc.gif
http://www.generalguitargadgets.com/diagrams/gringer_sc.gif
http://www.generalguitargadgets.com/diagrams/ftmsc.gif
http://www.fortunecity.com/tinpan/humperdinck/223/octave.gif
http://www.geofex.com/FX_images/blender.gif
http://www.diystompboxes.com/pedals/ousb.gif
http://www.geofex.com/Article_Folders/Screamer%20Octave/tsoctave.htm

I'll try to step through each one talking about the rectification stages to understand it more

[markphaser]

The Tychobrahe Octave is a 3 transistor stage with a coupling transformer. The frist and second stages are a tone eq stage the third is a driver stage. The coupling transformer takes the AC waveform and splits it into 2 signals flipped 180 degrees which is phase splitting. The diodes then fullwave rectifys both signals into DC waveforms so the negative half of a AC cycle is flipped over so you have 2 positive peaks and no negative half of a cycles now. Since we have only positive cycles and no negative cycle well we do but the phase splitter and diodes flipped it up so the frequency doubled two times in the same time period from the original thats how we get a octave up.

Octave up Time period- is twice the time period(frequency) of the original time period

[markphaser]

Foxx Tone machine:

Foxx Tone machine uses germanium diodes which add different harmonics than the silicon diodes.
The second transitor is the phase splitter. The caps before the diodes give a frequency range to add more harmonics in that spectum.The octave switch is a half or full wave recification mode selector.

Scrambler:

Q2 transistor has a diode from emitter to base that splits off to the rectification stage, the collector of Q2 goes to the recification stage also. The recification stage has the diodes this does a special recification with the order of the diodes which converts the frequency up.

Green Ringer:

Q2 transitor is a phase splitter stage which has .047uf caps then to the diodes which rectify the signal from AC to DC twice the frequency period of the orignal AC period/frequency. Q3 is a summing transistor which takes the 2 rectified DC signals and turns it back to AC signal for the output.

Roger Mayer Octavia:

transistor(3) is the phase splitter which has caps before the diodes, the caps before the diodes give
a frequency range for the diodes to rectify and distort at a frequency to give harmonics.
The main difference between the old jimi hendrix prototype octavio is that it was 18 volts NOT 9 volts so you have different voltage drops, more headroom, more current, the tone and frequencys change because of more voltage and current the operations of the circuit gives different results from the transitors and components giving different harmonics and overtones.


I tried my best to explain these circuits maybe some real cats can explain these better than me

[johngreene]

Actually if you want to talk 'theory' of octave pedals....

What they are all doing is a emulation of a multiplication of an ac signal with itself. A 4-quadrant multiplier (which were hard to come by back 'in the day', cheaply anyway) would take a time-varying input signal and multiply it by itself. Multiply something by itself (squaring) and the result is always positive (negative times negative is positive). So, the negative half of the input becomes positve. You can emulate this by simply full-wave rectifying, if the signal is 2-dimentional. So, you have a large variety of circuits that try to simply give the same result of a multiplication. Once you go beyond a binary phase multiplication, this is no longer so easily emulated.

--john

[Eb7+9]

What they are all doing is a emulation of a multiplication of an ac signal with itself.

depends if you accept |x| to be a close approximation to x^2 ...

~jc

[Paul Perry (Frostwave)]

depends if you accept |x| to be a close approximation to x^2 ...

True enough jc...... and who is to say which sounds best?
Hell, think I'm gonna have to rig up a couple of my AD633 ring modulators to give x^3....

[markphaser]

Two octave pedals in series goes up a octave more

[MartyMart]

Two octave pedals in series goes up a octave more

Yes, but they start to sound "shitty" when you do that !!

MM.

[johngreene]

Two octave pedals in series goes up a octave more

Actually that would be 2 octaves more.  2 * 2 = 4 not 3



--john

[Paul Perry (Frostwave)]

I can get x^3 from two of my AD633 ring modulator pedals, because there is a plug at the back for external carrier input. So, on the first Blue Ringer, I run the X to the audio input and to the external carrier, whihc gives me x^2.
Then, I run the output to the external carrier input of the second Ringer, and the original audio (via a splitter adaptor) to the audio input of the second Ringer.
Huzza! we now have x^3.....if we want it. And, using the wet/dry blend of the 2nd Ringer, you can mix up any blend of X^2 and x^3 (Should I have put a phase reversal switch in there? Maybe! but where?? )

[johngreene]

But wouldn't that be X3 instead of X^3? You get X^2 because you are multiplying the signal by itself. When you multiply this product by the orignal singal you get 3X and 1X for 'sidebands'. Not the cube.

--john

[markphaser]

Thanks guys for the information

What is the theory behind a octave up circuit?

How is the rectification done in a octave up based on electronic theory?

[Pedal love]

Well I had thought that all of these harmonics 1,3,5,etc are part of the whole sine wave. You can find them in there, but the octave(double) is unidirectional and can't be cancelled. That would explain the phase splitters in these pedals, filtering out a lot of harmonics, by somewhat phase cancellation. Not sure of the rectifier's role however. Never thought it did much more than flip the sine wave. It may double the peaks on the positive side, but its over the same period of time in relationship to the sine wave of origin, I guess. I really am not understanding as I thought frequency doubling, had more to do with the width of the signal and not the number of half cycles, on the positive side of a sine wave.pl

[markphaser]

octave(double) is unidirectional and can't be cancelled

What u mean by unidirectional and can't be cancelled?

phase splitters in these pedals filtering out a lot of harmonics, by somewhat phase cancellation

Does the phase splitter filter out the harmonics? or phase cancel?

[GFR]

http://www.geocities.com/gfr.geo/octave.html

http://www.gfrhpg.hpg.ig.com.br/octaves2.html

Also look at Munky's site for the "Mutantes Octave Article".
http://www.diystompboxes.com/smfforum/index.php?topic=38265.0

[markphaser]

Thanks those are some nice graphs and oscilloscope pictures

what is the theory of the rectification stages?

Why did they use the phase spiltter stages?

[Mark Hammer]

Thanks those are some nice graphs and oscilloscope pictures

what is the theory of the rectification stages?

Why did they use the phase spiltter stages?

Phase splitters are the simplest easiest and cheapest way to get two opposite-phase versions of the same signal.  Stick a resistor between V+ and the collector which is equal to the resistor between ground and the emitter and you have a phase splitter, which gives a signal at the collector opposite in phase and equal in amplitude to the one at the emitter. 

Since they are opposite in phase, all the peaks occur in one where the troughs occur in the other.

Chop the bottom half of each waveform off with a diode, and combine them and all you have are the peaks, except there are twice as many.  If you mix those two outputs together in the appropriate balance, you will hear what sounds like an octave.  This is why JC Maillet placed a trimmer in one of the phase-splittter outputs in his modded Green Ringer, and is also why some versions of the Superfuzz have a balance trimmer at thepoint where the two opposite phase signals are combined.  The need to have balance also explains why some octave-up units have a stronger octave sound than others - the effect of component tolerances on balance.

Why does it not sound like a digital pitch shifter set to an octave up?  Because the new output signal is made up of the positive half cycle of one of the outputs from the phase splitter, and the other half is madeup of the negative half cycle "flipped over" to mimic a repeat of the positive half cycle.  If you look on a scope image of normal guitar signal, what you'll see is that the negative half cycle of your guitar signal is not the absolute mirror image of the positive half cycle.  Consequently, this new "doubled" signal essentially alternates waveforms between successive peaks.

Perhaps more importantly, the new synthesized negative half cycle is just that portion of the waveform around the crossover point.  It should, in theory, have a waveform that is more or less independent of what's going on at the peaks.  In other words, both the positive and negative half cycles of this new doubled signal look/sound nothing like the original.  In a pitch-shifter the negative and positive halfwaves are preserved, but time-compressed so that when played/shifted an octave up they take place in less time.

[markphaser]

Thanks alot Mark Hammer

Is the output DC or AC because the diodes flip the negative cycle the positive and negative waveforms look DC on the output on the osciiloscope?

So they change the AC input to DC, flip the negative cycle to DC and then change the positive cycle and negative cycle DC to AC for the output?

Every octave pedal has a different way of rectifying the AC waveform to DC why is that? what is different about all these octave rectifying stages?

[Mark Hammer]

No.  Everything remains AC.

It may be sitting on a DC offset, but if it goes up and down (i.e., more positive and less positive), it is still AC.  Even if it is sitting on top of DC, whatever capacitor is placed in series with it will remove that DC, leaving only AC.

It seems to me you are misunderstanding what goes on with rectification.  Yes, it is true that when an AC signal is "rectified", it is for the purposes of producing something LIKE DC.  But this is a bit like the flatness of the earth.  We USED to think the earth was flat, but then we learned it simply took great distances for the actual curve of the earth to become apparent.  Diode rectification, followed by a smoothing capacitor (especially a large one) reduces the ripple of the AC signal so that is behaves sort of like DC.  Like the earth with a very gentle curve, that "DC" is still really and truly AC of a sort - it just has so little ripple left in it that we are permitted to think of it and use it like DC.

The ripple produced by full-wave rectification is, in principle, less than the ripple produced by half-wave rectifictation. I say "in principle" because the ripple is not only a function of the type of rectification but of the lag or slew imposed on it by smoothing caps.  The same AC signal half-wave rectified with a 10,000 cap to ground would likely have much less riple than if it were FWR'd but had a .001uf cap to ground afterwards.  Think of this as being like the difference between how curved the earth seems when lying on the ground and looking forward vs standing on a mountain top and looking.

[markphaser]

Thanks Mark hammer

So the rectification stage with the diodes is not DC but AC? because on the oscilloscope it looks like DC because there is no negative cycles just positive

What kind of rectification stage are these in octave pedals since its not change AC to DC and back from DC to AC these seems like a different rectification process in octave pedals