Octave devices?

[Mark Abbott]

I own and have built a couple of octave up pedals (Fender blender, Foxx Tone Machine, Univox Super Fuzz, Roger Mayer Octavia.)

I have heard that RG Keen came up with a better octave pedal that doesn't us the traditional rectification technique, I have seen RG's circuit though I haven't seen a layout for it. Has anyone come up with a layout for his circuit, or is there a better circuit than the ones I've mentioned?

To answer the question what do I consider better, basically a smooth sounding octave sound without the rough sounding added fuzz.

Thanks for your help.

Yours Sincerely


Mark Abbott

[RLBJR65]

Where is the schematic?

[tcobretti]

The other pedal you might want to try is the green ringer.  Both these circuits will have a little distortion, but these two shouldn't have much fuzz.

[Processaurus]

Has anyone gotten this MOS doubler to work?  I was intrigued but when I breadboarded it nothing came out.

[RickL]

I have. I built it on perf a couple of years ago and I'm sure I still have the layout (hand drawn on graph paper) somewhere in a large pile. I finally got a digital camera so if I'm motivated enough to find it this weekend I'll try to take a picture and post it somewhere. Don't hold your breath though, I have a bad habit of saying I'll do something then forgetting about it  .

It's been a while (approximately a couple of years) since I've played with it, but if memory serves it had a fairly strong upper octave that wasn't completely clean. Cleaner than the other options (Fender Blender et al) but not as clean as a digital pitch shifter.

Send motivational thoughts my way or send someone over with a big stick and maybe I'll find it.

[John Lyons]

Seems pretty simple with the pins numbered on the schematic but if you have a layout that would be great.
So it was fairly clean?

John

[petemoore]

  Yea warining I forget too !
  But that's a complicated build or tune job, not paint by number by any stretch, just remembering the vibe on it, not technically why, except that the mosftes have to be somehow matched or something, kind of a tricky wicket, IIRC.
  I had a  lot of good times but troubles keeping octaves going, rather than re-debug my 'recently gone 1/2 dormant' Tycho or GR, I opted to whip up a nice strong Bobtavia, I'm quite happy with him.

[Mark Abbott]

Thanks for the replies, particularly Pete Moore, I haven't heard from you in ages!
How is it all going?

I thought RG Keen's device might have had pitch shifter like quality without the normal octave upper symptoms.

It's my experience that to effectively use a rectifier octave unit, you must use your front pickup, use your guitars tone controls to roll off the upper frequencies, and pick lightly. It's all a bit much on the fly sometimes!

Again thank you for all the assistance, much appreciated.

Yours Sincerely

Mark Abbott

[Processaurus]

It's my experience that to effectively use a rectifier octave unit, you must use your front pickup, use your guitars tone controls to roll off the upper frequencies, and pick lightly. It's all a bit much on the fly sometimes!

This idea at least solves the tone knob part.

[oldrocker]

Not to change the subject but what does everyone think about the Neoctavia from home-wrecker.com.  I built this to get more gain then the GR and used the audio transformer from Radio Shack.  I also used 4148 SI diodes instead of germs and it sounds pretty good.  The 100k volume pot gets some nice gain and sounds similar to the Green Ringer with a little umph.  Not as clean as some would like I guess but it's cleaner then the Scrambler.

[Ben N]

It's my experience that to effectively use a rectifier octave unit, you must use your front pickup, use your guitars tone controls to roll off the upper frequencies, and pick lightly. It's all a bit much on the fly sometimes!

This idea at least solves the tone knob part.

The GFR essay is good, and there are also a number of threads here that deal, either primarily or incidentally, with using an LPF to optimize the signal for octaving. IIRC, RG had suggested somewhere doing a bunch of LPFs with succesively higher cutoffs, and some kind of logic to select the optimal one for the note being played, but I don't recall if this was in connection with octaving, noise reduction or something else, and it is probably overkill for this purpose, but interesting.
Ben

[g3rmanium]

To answer the question what do I consider better, basically a smooth sounding octave sound without the rough sounding added fuzz.

I think my squarer sounds pretty smooth and more like a ring modulator.

If you like the sound, the circuit diagram is here.

[tcobretti]

That squarer does sound and sound pretty good.  Does it work well below the 12th fret? 

[g3rmanium]

That squarer does sound and sound pretty good.  Does it work well below the 12th fret? 

It's different. I noticed that notes seem to stay mostly intact, but you can get some intermodulation trash that sounds a bit like a ring modulator. The frequency range where this will show up is mostly in the lows though.

[Mark Hammer]

Hi Mark,

Nice to see you around here.
My experience with octave-up units is that they suffer from doubling of harmonic content.  This is what adds the undesirable raspiness, as lower order and some upper harmonics get doubled.  Ideally, what one wants to do is to filter the signal portion being doubled such that it starts to reflect the sinusoidal waveform one often sees in illustrations  of FWR frequency doubling.  Not only does doubling of harmonics make the sound raspier, but it obscures the octave-up effect as the doubled fundamental gets lost amidst a haze of other harmonics.

Certainly one of the most robust octave-up (though not necessarily the cleanest) effects is the Foxx Tone Machine.  Looking here - http://www.generalguitargadgets.com/diagrams/ftmsc.gif - you will note the presence of a notch-like network between the base of Q1 and emitter of Q2, formed by R4/R5/R6 and C2/C3.  This is fairly unique among octave-up units, as near as I can tell, although there is a marginally similar network between the base of Q1 and emitter of Q2 in the Univox Superfuzz as well, just not identical.  I've built both and find the Foxx to have a superior octave-up sound in terms of hearing an obvious doubling of the fundamental.    The Superfuzz shows a clear impact of the using FWR but the *note* is not nearly as identifiable as with the Foxx.  This says to me that there is something worth examining in the FTM.

Of course, my comment about filtering of the signal echoes, in a general sense, the observations of many that more pleasing octave-up effects are obtained from the neck pickup, within a certain fret range, and with the guitar's tone rolled back a bit.  All of these are conditions that would mimic an input signal with appropriate lowpass filtering to make the doubling of the fundamental more obvious.  I supose that a tracking filter would be optimal, but clearly it would a) only be suitable for monophonic processing, and b) be far more involved a design than really ought to be the case for something like this.

I would be curious to hear of any experiments members have conducted, in which active filtering is used in an add-on front stage of an existing or DIY octave-doubling circuit.  The Green Ringer would seem to be one of the obvuious candidates for this, since the unit is about as basic as they come, has NO filtering of note, and offers what can be described as "fleeting" octave-up sounds.

I'd also be interested in a more theoretical explanation of what those base-to-emitter networks in the Foxx and Univox units are actually doing.  Are they somehow enhancing the fundamental prior to phase splitting and rectification?

[Mark Abbott]

Dear Mark

Thanks for the reply and like wise it is good to hear from you again too.   

Yours Sincerely

Mark Abbott