Octavio and Octave up Theory

[johngreene]

DC does not mean 'positive'. It means zero frequency. It can be either positive or negative. If you did a FFT (which would show the individual component frequencies of a composite waveform) on the signal you see on the oscilloscope you would find components at harmonics of (and including) the fundamental plus a large component at 0 hertz.

Full-wave rectification is possible by inverting the sign of the negative half of the cycle creating a sort of copy of the the positive half. Now you have 2 of something where you previously only had one. Thus the 'octave'. You need an inverted form of the input signal in order to achieve this which is why the phase splitter is needed.

The 'theory' behind rectification is that by the use of diodes, all current flows in one direction. From this you can average (filter) to get rid of the component frequencies and leave (mostly) DC. Diodes make this possible because they only allow current to flow in one direction. Kind of a 'one-way valve'.

--john

[markphaser]

thanks for the theory information

The Full-wave rectification stage is different in every octave pedal why is that?

Why does the designer have a special full wave rectification stage? does it change the frequency or pitch?

[johngreene]

thanks for the theory information

The Full-wave rectification stage is different in every octave pedal why is that?

Why doesn't every guitarist play through the same pedals? Why do people drive different kinds of cars? Why doesn't everyone eat hamburgers for lunch? Personal choice. I'm sure every designer thought they could do it better than anyone before them.

Why does the designer have a special full wave rectification stage? does it change the frequency or pitch?

It's an octave circuit, it generates twice the frequency of the input signal. If it changed the pitch or frequency, it wouldn't be an octave pedal.

--john

[markphaser]

Thanks

it generates twice the frequency of the input signal

Yes but the rectification stage each octave pedal does it different what are some ways of generating twice the frequency of the input signal ? from looking at the rectification stages of each octave pedal how are they different

[markphaser]

The rectification stage converts AC to DC but how does it change AC to DC and keep the frequency because DC doesn't have frequency?

[johngreene]

That question makes absolutely no sense.

[markphaser]

Does DC have frequency?

Because in a Octave pedal the rectifier stage they use diodes to change AC to DC?

But how do they get to double the frequency using DC because DC doesn't have frequency?

[gez]

Does DC have frequency?

Because in a Octave pedal the rectifier stage they use diodes to change AC to DC?

But how do they get to double the frequency using DC because DC doesn't have frequency?

Technically a full wave rectified AC signal is DC, only it's pulsating DC (which is why it's audible - it has frequency).  For it to be truly AC a change of direction is needed.  For our purposes though it's easier to think of it as an AC signal.

Mark, you obviously have a burning desire to fully understand the nuts and bolts of how circuits work (a good thing!).  For a really good intro into how AC works an excellent book on the subject is 'Basic AC Circuits' by John Clayton Rawlins (Newnes Publishing).  Expensive but it should make things a lot clearer.

[markphaser]

a full wave rectified AC signal is DC, only it's pulsating DC (which is why it's audible - it has frequency).  For it to be truly AC a change of direction is needed

The rectified stage changes AC signal into DC(frequency) pulsating waveform

Every octave pedal has a different rectified stage from change AC to DC frequency. It seem the DC frequency is set at a different frequency? thats why every octave pedal have a different rectified DC frequency?

[gez]

The rectified stage changes AC signal into DC(frequency) pulsating waveform

For our purposes though it's easier to think of it as an AC signal.

Every octave pedal has a different rectified stage from change AC to DC frequency. It seem the DC frequency is set at a different frequency? thats why every octave pedal have a different rectified DC frequency?

Read through the whole of this.  About half way through things should be a little clearer:

http://www.geofex.com/effxfaq/distn101.htm

[petemoore]

  Does DC have *frequency
  If it's switched on and off, or the polarity is changed...at a *frequency

[petemoore]

  I've matched values of some of the parts that contribute/detract from the symmetry of the signal in octaves, around where the wave gets folded.
  And...wondered if more pronounced Octave could better be found with the ability to 'tune' the symmetry...by varying 'something' on one 'side' to match the other, so that [maybe] more octave would become present...changeing the amount of preboost or wave squaring to get the 'neatest folded wave' possible.
   I'm still 'out' as far as how important the matching or tuning of an octave 'is', but Comparing clones from same Tycho schematic Green Ringer schematic [2 of same, each], they sound different.

[gez]

  Does DC have *frequency
  If it's switched on and off, or the polarity is changed...at a *frequency

If the polarity is changed at some point then it becomes AC.

A half wave rectifier working on a sine wave simulates the on/off switching you mooted.  It's still a pulsating DC voltage and will be audible (if the pulses are in the audio frequency band) just as ripple on a DC voltage is audible.

[markphaser]

So a octave pedal is just a higher ripple frequency? or a different ripple frequency? its the same as what ripple is? because the diodes in a power supply change AC to DC ripple just like a octave pedal so a octave pedal has a ripple frequency?

the matching or tuning of an octave?

How would i match the octave? how is matching the octave down?

Tuning of an octave? how is this done?

[gez]

So a octave pedal is just a higher ripple frequency? or a different ripple frequency? its the same as what ripple is?

In most of the circuits we build an AC voltage is coupled through to an amp that is DC biased and it 'rides' on the back of this DC voltage.  A cap at the output blocks the DC again and only AC is allowed to pass.  I gave the ripple analogy to answer Pete's question, I was trying to explain that DC voltage needn't be a fixed thing - it can have many forms...well, not that many.  As far as octave circuits go, do yourself a favour and just think of the signal as AC.

I don't understand your other questions.  If you really want to understand theory/circuit analysis better you have to do some reading.  Asking questions here will only get you so far.  The bottom line is you need to have a basic understanding in order to interpret a lot of the advice that is being given and the only way to do that is through study.

This stuff takes time and effort.  Do yourself a favour and use the search function to look for 'books'.  Make a note of some and get stuck in, until you've got a better foundation there's not much point asking the questions you're asking.

I'm sure there are some who'll disagree, or who are willing to answer your questions ad infinitum, but that's the way I see things...

[markphaser]

Thanks

How can the signal be AC if its been Full wave rectified?
because it has DC offset? but still the output is going to block the DC

[markphaser]

how does the rectifying stage in a octave changes the AC frequency?

On the oscilloscope it looks like Ripple DC but have a higher frequency
so how is it still AC if it looks like ripple DC?

Most octave pedals rectifying stage double or twice the frequency at the same
time period is there a way to change the overtones/harmonics in a octave pedal?

[markphaser]

The rectifier section rectifys AC signal and it looks like DC but its actually AC signal still because its has frequency

This is the "Heart" of the octave pedal each octave pedal puts the diodes in different places to rectify the guitar signal.

The rectify section takes the audio signal and produces a "octave up" . Every octave pedal does this "octave up" rectified section different what are some ways of doing this?

What this is doing is AC recification which means its taking a AC signal converting it to a high frequency AC signal way different then a power supply recification is doing

Octave pedals have "phase inverter" to split the signal then rectify's the upper and lower part of the waveform

I'm trying to make a "octave doubler" instead of of a octave up how do i do this?

How do i change the octave up? like change the Q point, the Resonance frequency,

HOw do i change the rectification of the octave up? so its not so quacky like a Fixed wah notched out sound?