# diode octave



## keeperofthegood (Apr 30, 2008)

Hey oh

Has anyone got a sound clip example of before and after of diode doubling? I just tried it and it sounds rather bad, have to really drive the guitar to get anything out of the amp etc. so wondering if anyone has a demo on this so I can 'hear' what it should sound like?

I tried 1N4148 fast recovery silicon switching diodes in a full wave bridge direct from the pickup to the amp (no vol or tone in the guitar).


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## mhammer (Nov 30, 2007)

I think you'll need to further articulate what you mean. When you say "diode doubling" do you mean using a 2+2 diode complement for clipping, or do you mean use of diodes to produce octave doubling?


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## keeperofthegood (Apr 30, 2008)

http://falstad.com/circuit/#$+1+5.0...35+10.0+0.05+0+-1
o+12+64+0+35+5.0+0.05+1+-1



Using the diodes as a doubler like that, putting the guitar pickup in place of the 40hz source and amp in place of the load resistor.


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## mhammer (Nov 30, 2007)

Sorry. Not working for me. Can you post a screen dump of what you're talking about?


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## keeperofthegood (Apr 30, 2008)

Here we go (photobucket is a pita on the new compy at the moment) a google of it (more or less). Guitar as the AC in and the DC out is the doubled signal (flipping the negative half wave up essentially). Using http://en.wikipedia.org/wiki/1N4148 diodes in this.


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## Guest (Oct 24, 2011)

You're trying to rectify a guitar signal? That's not going to turn out well. 

FWIW I've never heard of this referred to as doubling before. This is rectification.

What are you hoping this circuit would do for your guitar signal?

You're creating a really inefficient signal for an amplifier to amplify. Because the signal changes instantaneously at the zero line you're causing the speaker to switch it's direction of travel instantaneously. That's going to be hard for it to do.


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## keeperofthegood (Apr 30, 2008)

LOL Ian, it is how I understand it to work. It is yes rectified but on the DC side unfiltered what you have is a doubled signal of the input. On power line voltages in 60HZ becomes 120HZ before it is filtered only in this case you don't filter it you use it as-is.

http://www.techlib.com/files/diodedbl.pdf

Fig 1 top one. The transformers are not necessary to the process, and this 'should' double the signal. I know there are a few means that people have used for using the 'diode doubler' concept (most recently discussed in the effects for vocals thread) but my google of that was a fail last night so since my experimental guitar is open I just went in with the four diodes as my starting point ... and found it didn't do what I had expected. So, hence the post asking what this is supposed to sound like.


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## mhammer (Nov 30, 2007)

keeperofthegood said:


> Here we go (photobucket is a pita on the new compy at the moment) a google of it (more or less). Guitar as the AC in and the DC out is the doubled signal (flipping the negative half wave up essentially). Using http://en.wikipedia.org/wiki/1N4148 diodes in this.


Okay, now I get it. You're referring to octave doubling via full-wave rectification. As the illustration shows, each half cycle of the signal is separated out, by means of the diode's properties, and then the complementary half cycles of each "version: of the wave are recombined such that, where there used to be one peak, there are now two.
The vast majority of analog octave fuzzes (Green Ringer, Fulltone Ultimate Octave, Superfuzz, Fender Blender, Foxx Tone Machine/Dano French Toast, Octavia, etc.) use a variant of this approach, some in more obvious ways than others. What you will note is that when the composite signal shown as "5" is formed, while there may be two peaks instead of one, the resulting waveform (take out the hatching) is in no way symmetrical. The bottom half doesn't look _anything_ like the top.

So It produces something which provides something that sounds like an octave up, it is NOT the same as a true pitch shifter doubling everything that comes in. It's not the same in a few ways. First, the harmonic content in the negative-going half cycle is different than the harmonic content in the positive peaks. Obviously guitar signals are quite complex, but even if you fed the circuit a pure sine wave, you'd have no harmonics on those round peaks, and lots of harmonics in the triangular-looking dips.

The other difference is that the positive-going peaks have no real ceiling on them, while the negative-going peaks are more or less "clamped" at a fixed voltage. So the dynamics on the waveform have gone from symmetrical (same for peaks and troughs) to asymmetrical.

In general, such "doubling" depends very much on the matching of levels between the two halves of the signal to achieve audible doubling/octaves. If the "folded over" portion is a higher amplitude or lesser amplitude than the other half cycle, then you get a taller-lower-taller-lower peak, which is not going to be heard as twice the frequency.


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## keeperofthegood (Apr 30, 2008)

Thank you Mark  so expect it to sound more nasty than not. I see most are using phase splitters for the source and mixing the signal back with diodes, the octavia doing the full wave rectification at the end. So, I am going to figure what I have will work but I am losing on that 0.7 volt diode loss. Will try this with a pre-amp and see how it goes. I really should get a few of the 42's http://ca.mouser.com/Passive-Components/Transformers-Audio-Signal/_/N-5gbg?Keyword=42 they seem to pop up a fair bit in small projects like these.


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## mhammer (Nov 30, 2007)

The 18 and the 22 seem to be used frequently.


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