# Alex's Octave-Up Rabbit Hole



## finebyfine (Dec 15, 2021)

*ex post facto introduction:*​Analog octave up is easily my favorite effect. Throw a good fuzz on top or in it and you have the basis for my favorite guitar sounds. I love how it works with doom metal (eg, the EQD Life Pedal using a Green Ringer, the Boss Super Fuzz being used all over the place in the genre, etc), psych rock (Octavia, etc) and anything in between and all over. I love the textures they make with chords, and love how they make single notes shine. 

In this thread I've documented some of the digging I've done into analog octave up and related circuits & topographies for frequency doubling and squaring.  Other than this intro, no other posts have been edited that much after the fact. 


Can’t find too much from googling but has anyone seen an op-amp precision full wave rectifier used in any octave circuits?

I was digging into phase inversion correction and got introduced to the concept.  am gonna be breadboarding a few when I have some free time. Hard to beat an octave fuzz in my opinion and I don’t recall seeing it done this way in a circuit I’ve looked into.

Overview:  https://circuitdigest.com/electroni...wave-precision-rectifier-circuit-using-op-amp


TDPRI thread with examples: https://www.tdpri.com/threads/the-groble-green-ringer-octave-blend.326950/#post-4169518

Circuit from above that author recommends with a buffer and low pass filter, with variable R3 allowing for a similar effect as the green ringer nuller mod


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## finebyfine (Jun 14, 2022)

I wanted to document some research I've done on this topic and also ask for some guidance.

The late Time Escobedo had several op-amp rectification based octave up effects in his Folk Urban circuit collection.

His Rambler (and Marginally Better Rambler) are fuzz heavy octave fuzzes, and the Octup Blender is the closest to a textbook op-amp rectifier as far as I can tell.





When I breadboarded it, it's octave effect was less dependent on typical octave up playing conditions (neck pickup, playing above 12th fret, tone knob all the way down) than others, including Anderton's Green Ringer (EQD Tentacle, PedalPCB Squidward) which is the gold standard in my opinion.

My main question about the Octup Blender is about the voltage divider Vr: this is done so that the input signal is not clipped to ground like it would be in a single supply op amp, right? If this is true would there be any benefit to using a voltage inverter to create a larger supply rail difference instead of a divider? I've breadboarded _other _op-amp rectifier circuits using this method but couldn't tell much of a difference in effect.


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## benny_profane (Jun 14, 2022)

I'm a little confused by your question. Using Vc/2 as the signal reference is SOP for single supply op-amps. If you were to use a single supply op-amp (V+ = 9V, V- = GND) and your signal was referenced to ground, you'd only have a positive swing. You could use a dual supply for the op-amps and eliminate the voltage divider and reference the signal to GND if you wanted, but I'm not sure if you'd need the added headroom/the design warrants that. I don't believe the signal is approaching the rails here.


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## finebyfine (Jun 14, 2022)

benny_profane said:


> I'm a little confused by your question. Using Vc/2 as the signal reference is SOP for single supply op-amps. If you were to use a single supply op-amp (V+ = 9V, V- = GND) and your signal was referenced to ground, you'd only have a positive swing. You could use a dual supply for the op-amps and eliminate the voltage divider and reference the signal to GND if you wanted, but I'm not sure if you'd need the added headroom/the design warrants that. I don't believe the signal is approaching the rails here.



Yep headroom is exactly what I meant and the phrasing that was on the tip of my tongue. Thanks!


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## benny_profane (Jun 14, 2022)

With a circuit this small, I'd set up an A/B test on the breadboard and switch between the two power options. I doubt that you'd hear a difference.


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## finebyfine (Jul 26, 2022)

A few updates for this thread:

Another pedal circuit based on precision rectifiers is JC Maillet's Super Full Wave Octaver:





Super clean octave up, even on bright bridge pickups. Crazy fun build.

I've also been digging into ring mod circuits to do octave-ish up. This LM13700 one is up next for the breadboard. 




Trying to see where this gets me because AD633 ring mods and similar (EHX Frequency Analyzer - madbean freekout is a clone) are pretty complex for what I'm going for, plus analog multipliers ICs are not cheap.


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## finebyfine (Aug 28, 2022)

I have been really wanting to avoid spending $12 on an AD633 but I'm waiting on that, and also an SMA5101 - which is 4 NPN transistors arranged as a Gilbert Cell - which is the basis for as far as I can tell, most analog multipliers, but especially the AD633.

This is what I'll be starting with on the AD633, from the AD633 datasheet for frequency squaring


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## Bricksnbeatles (Aug 28, 2022)

Rad! Gotta give this a try


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## finebyfine (Oct 7, 2022)

Some more updates mostly for my own record. No demos unfortunately.

I've been playing around with two analog multiplier ICs: Analog Device's AD633, which is at the heart of a lot of more recent ring modulator pedals, and the obsolete, but cheap (like $1-$2 a pop, compared to $15-$20 AD633) and plentiful Exar XR2208. The bounceless frequency squaring application note in the AD633 datasheet is pretty good out of the box running at ±9V - which has been a relief considering all of the schematics I've seen using ±15V. For the XR2208 I've used ixtern's circuit from their amazing ring modulator thread.

I was really hoping to be more blown away by the AD633 in terms of not having to do the typical octave-up playing considerations (neck pu, above 12th) but I am mostly chalking that up to just needing to dial it in better and spend more time with it.

Because of the price and availability despite being obsolete, I'm really trying to nail the circuit with the XR2208. The only datasheet with application notes I've found is the datasheet for the XR22*2*8 multiplier which is similar but has a few quirky differences.

Also next up after/alongside tightening up the 2208 circuit is to play around with frequency division. My ideal octave up ringer is still the end goal but it's listed in the AD633 datasheet and looks like a fun one.


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## finebyfine (Dec 25, 2022)

Another update for posterity!


I haven't gotten around to playing with the XR2208 and AD633 as much as I've been wanting to. Still on the short list
I've read through Ray Ring's H11F1M optofet designs documented on his blog, Circuit Salad (I've built this compressor he designed) and am especially interested in his H11F1M Ring Modulator that uses an H11F1M as a mixer. I still don't really understand how it works, nad with the XR2208 and AD633 it's low priority, but interesting nonetheless.
I got boards made for JC Maillet's "Green Ringer Redux". I'm having trouble finding a link to a blog post from him about it, but the URL at the bottom of this schematic is at least his source of the circuit.

This is _not_ his previous Green Ringer Mod circuit with a tone toggle and nulling mod, drawn on the GGG schem, that is easy to find on his lynx site. In his schematic of this version, in fact, he has omitted the nulling mod altogether.

The Fuzz control turns it into a *wild *octave fuzz. But because my goal here is really more towards semi-clean Octave Ringing, I haven't used it much while playing with it and there are better octave fuzzes if that's the goal. I do turn it up in the demo below.

I kept potentiometers for both sides of the common "nulling" mod. Having both of these pots external is definitely overkill. If I redid the boards/schem I'd still keep one external, and have the other either be a set resistor value like in traditional null mods, or keep the other as an internal trimpot.





Here is a very sloppy (and long) demo of it in use.


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		https://soundcloud.com/finebyfine%2Fgreen-ringer-redux-demo%2Fs-xCV5v6EBz3R

At around 3:50 in I switch to my amp's dirt channel - which is really why I love from cleaner octave up circuits, that is, having the octave up be on the cleaner side so I can choose how to color / fuzz it up.


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## Bricksnbeatles (Dec 25, 2022)

finebyfine said:


> Another update for posterity!
> 
> 
> I haven't gotten around to playing with the XR2208 and AD633 as much as I've been wanting to. Still on the short list
> ...


Rad! I must try this out. I’m a big ringer fan


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## swyse (Dec 25, 2022)

Got any clips of JC Maillet's Super Full Wave Octaver? Your description of it sounds very intriguing.


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## finebyfine (Dec 25, 2022)

swyse said:


> Got any clips of JC Maillet's Super Full Wave Octaver? Your description of it sounds very intriguing.



I was surprised I didn't have one, so here's a quick one. The noise floor on this build seems a lot higher than I remember it being but my amp also sounds more noisy than it did when I recorded the redux demo earlier today. I switch to dirt around 1:45


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		https://soundcloud.com/finebyfine%2Fsuper-full-wave-octaver-demo


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## swyse (Dec 25, 2022)

finebyfine said:


> I was surprised I didn't have one, so here's a quick one. The noise floor on this build seems a lot higher than I remember it being but my amp also sounds more noisy than it did when I recorded the redux demo earlier today. I switch to dirt around 1:45


That sounds super fun, thanks for the demo! Do you find the "second" control to be a useful enough to put external?


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## finebyfine (Dec 25, 2022)

swyse said:


> That sounds super fun, thanks for the demo! Do you find the "second" control to be a useful enough to put external?



It's much more useful with a log pot than a linear one - with a linear in this build I've mostly just kept it dimed. I just didn't have any A100ks on hand (somehow! I probably have 30 in my parts cabinet now) when I got the PCBs in for it. With a log pot you can really hear it focus in and out more like nulling a green ringer.


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## DGWVI (Dec 25, 2022)

finebyfine said:


> I was surprised I didn't have one, so here's a quick one. The noise floor on this build seems a lot higher than I remember it being but my amp also sounds more noisy than it did when I recorded the redux demo earlier today. I switch to dirt around 1:45
> 
> 
> __
> https://soundcloud.com/finebyfine%2Fsuper-full-wave-octaver-demo


The sounds at about 0:50 - 1:15 are awesome.

This would make a rad project


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## finebyfine (Dec 25, 2022)

DGWVI said:


> The sounds at about 0:50 - 1:15 are awesome.
> 
> This would make a rad project


Happy to send you a board if you’re in the US - just dm me ya address


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## DGWVI (Dec 25, 2022)

finebyfine said:


> Happy to send you a board if you’re in the US - just dm me ya address


Might kind of you, DM incoming


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## phi1 (Dec 27, 2022)

Since you guys are octave up enthusiasts, I thought you might appreciate this. I recently built a couple double-analog-octave up pedals. Basically it’s just 2 green ringers in series, with a toggle to select one or both and of course the footswitch to bypass the whole thing.

The second circuit brings in a whole new sound. You can just barely hear the 2nd octave on certain notes, but mainly it just makes it more pinchy / nasty / aggressive (awesome with fuzz after it). It behaves similarly to the regular green ringer in that it works best with neck pickup playing up the neck.

Once I get around to making a little recording I’ll post a build report. You could of course use the concept with the other octave up circuits.

I attached a graph of what I think is approximately happening with the signal when the 2nd octave circuit is engaged. I did change the input capacitor of the 2nd circuit from 47n to 10n to help that high pass filter (DC coupling cap) work a little faster in theory. The difference is subtle but I think it’s there.

I can’t say if I like it better than the single octave, they’re both cool in their own way, which is why it's great to have the toggle. I have couple more boards I could send if anyone is interested!


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## finebyfine (Dec 27, 2022)

phi1 said:


> Since you guys are octave up enthusiasts, I thought you might appreciate this. I recently built a couple double-analog-octave up pedals. Basically it’s just 2 green ringers in series, with a toggle to select one or both and of course the footswitch to bypass the whole thing.
> 
> The second circuit brings in a whole new sound. You can just barely hear the 2nd octave on certain notes, but mainly it just makes it more pinchy / nasty / aggressive (awesome with fuzz after it). It behaves similarly to the regular green ringer in that it works best with neck pickup playing up the neck.
> 
> ...



Oh wow this sounds awesome - I'd definitely appreciate a demo if you can. Your graph seems right on to me in terms of what's happening. How does it play with multiple notes and chords?

I'm for sure gonna try something like this. I'm interested in how a blend on the second octave would sound, or hell, maybe feeding the output of a ringer back into itself a bit. The Carlin Ring Modulator can kind of do that if I'm remembering correctly.


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## Feral Feline (Dec 27, 2022)

phi1 said:


> Since you guys are octave up enthusiasts, I thought you might appreciate this. I recently built a couple double-analog-octave up pedals. Basically it’s just 2 green ringers in series, with a toggle to select one or both and of course the footswitch to bypass the whole thing.
> 
> The second circuit brings in a whole new sound. You can just barely hear the 2nd octave on certain notes, but mainly it just makes it more pinchy / nasty / aggressive (awesome with fuzz after it). It behaves similarly to the regular green ringer in that it works best with neck pickup playing up the neck.
> 
> ...



+1 for a Demo!




For several years, I've wanted to build an effect with a toggle switch, and this might be the perfect effect for that idea.
Was to be an OD with a toggled fuzz-boost, but this lends itself even better as there'd be no knobs.

Plan is to build the following into it:







Except I'll have to add a 555-timer that ramps up slowly.

1st push, 30 seconds before it turns itself off.
2nd push, 15 seconds before it turns itself off.
3rd push, 3 seconds before it turns itself off.
4th push, 0.5 seconds before it turns itself off.

Have a 3D-printed skeleton hand that comes out from under a "VU-Meter"
Build it, then gift it to a friend that doesn't know what it does.

"Hey, where'd the sound go?"


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## phi1 (Dec 27, 2022)

It sounds roughly 2x as bad as the green ringer with chords haha! I’ll try to record something soon


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## finebyfine (Dec 27, 2022)

phi1 said:


> It sounds roughly 2x as bad as the green ringer with chords haha! I’ll try to record something soon



Lol you’re talking to someone who basically started down this rabbit hole because of how much I love how chords sound through a green ringer! My curiosity is piqued now lmao


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## DGWVI (Dec 27, 2022)

finebyfine said:


> I'm for sure gonna try something like this. I'm interested in how a blend on the second octave would sound, or hell, maybe feeding the output of a ringer back into itself a bit. The Carlin Ring Modulator can kind of do that if I'm remembering correctly.



The Green Ringer works well with a feedback loop. Gets super 8-bit sounding. If you try it out, make the bias on the first stage adjustable for more intense fuzz tones


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## DGWVI (Dec 27, 2022)

Had to whip a couple Ringers up because I was disgusted with myself for not having one on hand. Built one stock, and the other to updated Parentheses specs- I prefer the latter

Anyway, the feedback mod- I can't find my build notes or video from the one I'd made, but I'm guessing it had other circuitry to make the feedback loop more stable. I'll keep tinkering and report back

Also, if you have some sort of resonant low pass filter (I used the Micro V clone set for no sweep), drive it into the Ringer. Delightfully disgusting


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## Feral Feline (Dec 27, 2022)

A demo of the resonant filter with Green Ringer would be fantastic. *hint hint*


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## DGWVI (Dec 31, 2022)

Feral Feline said:


> A demo of the resonant filter with Green Ringer would be fantastic. *hint hint*


Didn't see this until now, but I'll try to whip up a demo in the next few days


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## phi1 (Jan 2, 2023)

Here's some phone clips playing through the Double Analog Octave pedal I made.  Hope it's enough to give the flavor of the concept.  The higher octave isn't always apparent but, that mode always gets nastier.

First clip (all Les Paul Neck pup):
Clean
Clean + 1 Octave
Clean + 2 Octave

Second clip (all Les Paul Neck pup):
Fuzz
Fuzz + 1 Octave
Fuzz + 2 Octave

then at the end I was just toggling between single / double octave.

The second clip is some chords per finebyfine's request!
Clean
Clean + 1 Octave
Clean + 2 Octave


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## Feral Feline (Jan 3, 2023)

Sounds fantastic!

It's the sort of sound Reeves Gabrels would dig.

It's harsh in a good way, somehow avoiding ice-pick pain while still being a brutal sonic onslaught.

I know it's adding all sorts of harmonics, but the feel is one of deconstructionism.

Thanks for the demos!


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## finebyfine (Jan 3, 2023)

@phi1 oh my god I'm loving the chords one, thank you so much for that demo. Some great sort of nastier-fuzz on the single notes too in a really interesting way. Definitely on the short list to do this myself


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## Chuck D. Bones (Sunday at 2:38 PM)

Your problem with the LM13700 circuit is you're driving it too hard.  Either the 10K need to be bigger or the 33K needs to be smaller.  You're powering it with ±9V, right?


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## finebyfine (Sunday at 4:33 PM)

Chuck D. Bones said:


> Your problem with the LM13700 circuit is you're driving it too hard.  Either the 10K need to be bigger or the 33K needs to be smaller.  You're powering it with ±9V, right?



I was doing that one was just from a single 9V supply I think, with the inputs biased to 4.5v. Been a while since I played with it


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## Chuck D. Bones (Sunday at 6:02 PM)

So the schematic you showed is not what you built?


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## finebyfine (Sunday at 7:57 PM)

Chuck D. Bones said:


> So the schematic you showed is not what you built?


Just checked some photos I took and I actually didn’t bias it - I built it as posted


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## Chuck D. Bones (Sunday at 8:05 PM)

That would explain why it sounded bad.


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