Octave effect on Green Ringer

[mordechai]

I just bread boarded a green ringer, and I'd like for the octave effect to stand out a bit more.  Can anybody suggest a few tweaks that might help give it some greater presence?

[Buzz]

Make sure your components are well matched.

If we take this schematic:

http://www.generalguitargadgets.com/pdf/ggg_gro_sc.pdf

You would be trying to match the following components...

D1 with D2,
C2 with C3,
R5 with R6,
R7 with R8,
R9 with R10.

The diode matching being the most critical.

Also look up 'green ringer null mod', that helps too.

Lastly, don't expect too much. The green ringer just is what it is. If you want a greater octave effect you might have to go with a more complex circuit.

[duck_arse]

I thought I'd seen something recently on this, but still found these using the button:

http://www.diystompboxes.com/smfforum/index.php?topic=84116.msg700964#msg700964
http://www.diystompboxes.com/smfforum/index.php?topic=88395.msg746070#msg746070
http://www.diystompboxes.com/smfforum/index.php?topic=74157.msg607337#msg607337

it's the principle that counts.

[petemoore]

  GR bears similarity to the rectification sections of stronger octave circuits. Most of those circuit-sections [that resemble the GR] in say Kay, Superfuzz or FTM see boosted/shaped signal inputs.
  By driving the GR with a FF [nice tonal variety] or other such as Dist+, result in much stronger octave/harmonics and less gating splatter. 
  I find the GR is quite easily managed on my PB, and prefer that Dist or Fuzz are dialed in, on, and the Octave/Ring mod tone added from there.
  It works into the Boost+Dirt+Octave layering effect...amp set for guitar, boost dialed in firstly [this could become the basic clean tone], then Dist and Fuzz [dialed in mostly to be rythm/lead crunch with the dialed boost on], octave.
  I like the character of the ringmod/octave GR sound, and that the 'base-tone' [dirt sound] is retained in the sound, making a more seamless dirt to octave sw transition [IME].
  It can be a little like tuning a carburettor-boost [what feeds the 'distortion engine'], the engine [Dist+ or FF are good examples of tunable ''distortion-engines' that may like boosted input], and then the exhaust [octave], they all have their 'windows' [where their effect ''focused'' by dialing or tweeking] of preferred effect. I've simply 'bolted' the ringer onto the tail end of my first two layers [boost/boost+dirt] and enjoyed the shifting harmonic/octave effects with little or no tweeking of the GR.
  I've built a few, it didn't seem to matter when I made one with the 'mirror' components [divider resistors for Q1 and elsewhere] and diodes closely matched, but transistor swaps can make response change. It is typically fed a strong, distorted and assymetric signal anyway in my case.   

[Mark Hammer]

More robust octaving can be tweaked by matching the two rectified halves of the signal that are summed to produce frequency-doubling.  But the most robust octaving seems to involve a more complex front end than the GR has.  Take a look at the Foxx Tone Machine, and you'll see a vaguely Fuzz-Face-like front end, but with a more complex feedback loop between Q2 and Q1.

I also wonder how much any octaving that is produced in the GR ends up getting buried underneath all the extra harmonic content.  I keep wondering if running some small caps in parallel with the 68k resistors, or maybe a small cap between the base and collector in Q1, to provide a little lowpass filtering, might not be a bad idea.

[Eddododo]

look up 'green ringer null mod'

there should be something on viva analog, if i remember correctly

[mordechai]

More robust octaving can be tweaked by matching the two rectified halves of the signal that are summed to produce frequency-doubling.  But the most robust octaving seems to involve a more complex front end than the GR has.  Take a look at the Foxx Tone Machine, and you'll see a vaguely Fuzz-Face-like front end, but with a more complex feedback loop between Q2 and Q1.

I also wonder how much any octaving that is produced in the GR ends up getting buried underneath all the extra harmonic content.  I keep wondering if running some small caps in parallel with the 68k resistors, or maybe a small cap between the base and collector in Q1, to provide a little lowpass filtering, might not be a bad idea.

Mark, the idea of parallel resistors with the 68k resistors is something I will try.  What value range would be good to experiment with? Maybe 100-220pf?  Or would that be too subtle?

Also, how would  changing the 68k resistors to a different value (say, 47k) affect the signal?  Just asking out of academic curiosity.

[Mark Hammer]

Actually, looking at it again, I'm wondering if the 68k resistors aren't more for feeding 1/2V+ to the diodes.  So nix that suggestion.  But if you have a circuit that's working, and easy to just tack some caps onto, you may as well try it and see if it does anything useful.  I'd start with 470pf, and move up or down from there, depending on what you hear.

[thehallofshields]

I also have a GR on breadboard this week, and I can't emphasize enough how important the LP Filtering is. It doesn't fix the summing/difference effect that produces unexpected notes (try playing +1oct, +minor 3rd, like an E and a G an Octave above together for an example) that Mark has described in a thread I can't find right now.

However, LP filtering does greatly reduce the mess of harmonics that add a scuzzy, metallic, 'sting' to the sound. Try this: http://www.diystompboxes.com/smfforum/index.php?topic=32326.0 and see what you think.

[thehallofshields]

Mark, I've read many comments of yours about your Dist+ driven Scrambler, and I know you're not exactly a huge fan of the Ringer circuit.

For a long time I've wanted to ask you if you think that, minus increased gain and the Blend and Intensity controls of the Scrambler, the Rectification Effect is really any different from the Ringer (or Opamp driven Rectifier Octaves).

I think people often gravitate towards the Ringer because it can seemingly produce a more clean sound, albeit kind of weak. I'm really wondering if the Scrambler's difference in sound is really just from a more powerful (and bassier) input signal, or if there is really something different going on in the Phase-Splitter and Rectifier sections.

[Mark Hammer]

The Ringer uses a transistor-based phase splitter.  If you have equal-value emitter and collector resistors (10k in the case of the GR), you get equal-amplitude outputs from the emitter and collector that are 180 degrees out of phase with each other.  The diodes simply "chop off" the half portion of the signal you don't want.    Mix those selected half-signals together and you get something very close to doubling.  Since the diodes lop off not only the unwanted half-cycle, but also any part of the desired half-cycle that doesn't reach the diode's forward voltage, ideally you'll want to use diodes with the lowest possible Vf you can find.  This would probably be selected Schottky types.

In the case of the Scrambler, it uses a different, but related, method.  The two "versions" of the signal are each taken from the same transistor output, and created by passing them through a pair of diodes that are oriented in opposite manner.  Their blended (via the Texture control) mix is then fed back to the base of that transistor.  No such feedback is employed with any of the phase-splitter octave fuzzes, like the Superfuzz, Foxx, Fender Blender, Green Ringer, et al.  This is presumably one of the elements that gives the Scrambler both a different sort of sound, and a more intense sound.

Personally, I don't know how to do it, but I would imagine that if a DC voltage could be introduced to each of the complementary signals from a phase-splitter, then that half of the signal could theoretically be "chopped" by the diode very very close to the zero point.  That is, you would only lose the half cycle, and not 250-600mv more than the unwanted half-cycle.  In theory, that would/should result in a more accurate frequency doubling, with less of the unwanted harmonic hash that comes from the crossover distortion the diodes normally introduce.

Is this what the old GEOFEX MosFet doubler attempted to do?

[thehallofshields]

Mark, thanks for another great explanation of the Ringer circuit. I guess the Scrambler had me a little... mixed up...

For balanced Rectification, is matching the Voltage-Drop across the Diodes what it's all about? Is there any other point of balance that is really worth paying attention to?



For example, my breadboarded circuit has 2 Ge Diodes with a 100k Trimmer replacing the 2 68k resistors. With just single-coil pickup noise going through, the diodes appear to drop about 17mV each. (Of course, when I play a note this will jump over 500mV and the multimeter can't keep up with the change.)

What is that 17mV that I'm measuring across the Diode? I would think that with the 'trickle current' trick the potential difference across the Diode would be just below 300mV.

[Mark Hammer]

For balanced Rectification, is matching the Voltage-Drop across the Diodes what it's all about? Is there any other point of balance that is really worth paying attention to?

Well, the two half waves should be matched as much as possible, to achieve a more audible doubling.  In an older issue of Electronotes, the seemingly indefatigable synth/electronics guru Bernie Hutchins (how old is he now?) notes that equal-amplitude signals from phase-splitters like the one shown actually want/need emitter and collector resistors that are slightly different.  I forget which one, and Steve Bragg from Empress Effects still has my binder of Electronotes, containing the document, so I won't make any definitive statement.  In the absence of more info, I'll suggest that maybe the smart thing is to use a 9k1 fixed resistor and a 2k trimmer, to make either the emitter OR collector resistor just a smidgen higher, or lower, than its counterpart, and see what that does..

...What is that 17mV that I'm measuring across the Diode? I would think that with the 'trickle current' trick the potential difference across the Diode would be just below 300mV.

Beats the hell out of me.  I'm a psychologist, Jim, not an engineer.

[duck_arse]

I don't know from, but maybe the 68k's are providing isolation, one diode from the other, from the bias point. maybe even setting the impedance, one way or the other. perhaps if you connect one of the 68k to its own divider string, 15k//10k trimpot (68k to wiper)//15k, there might be some action?


[edit :] oh, and I only typed that above because I wanted to add - bones: "dishwashing liquid?"

(or something about plastercasting, now I look again.)

[Eddododo]

Personally, I don't know how to do it, but I would imagine that if a DC voltage could be introduced to each of the complementary signals from a phase-splitter, then that half of the signal could theoretically be "chopped" by the diode very very close to the zero point.  That is, you would only lose the half cycle, and not 250-600mv more than the unwanted half-cycle.  In theory, that would/should result in a more accurate frequency doubling, with less of the unwanted harmonic hash that comes from the crossover distortion the diodes normally introduce.

I believe that's what the Voltage dividers that insert right before the diodes are there for; biasing the diodes 'on' a little bit

[Mark Hammer]

Now that you made me think about it, you may be exactly right.  If that's the case, maybe the "ideal" GR involves throwing the post-diode signal on a scope, and tweaking the (nominal) 68k resistance until the "right amount" of that half-cycle is achieved.  Never thought of it that way before, but it sounds plausible.

Thanks!

[Digital Larry]

What I'm about to offer has yet to be tested by me, but since you are in the middle of building such a device maybe you can try it and let me know what happens.

The theory goes like this:
If you have a perfectly balanced rectifier, the "octave" effect for a complex signal going in will be enhanced if the signal coming in is symmetrical.

I got this thought from reading Joe Gore's "Tonefiend" blog where he mentioned that there's a "sweet spot" for getting the octave out which is to play around the 7th fret.  However, I think that is coincidental because playing at the 7th fret puts your (typical) picking position at about halfway along the fretted string.  If you plucked near the bridge then the 7th fret would no longer be the sweet spot.  Plucking at the halfway point is the best way to get a symmetrical signal out of a guitar.  Such as plucking at the 12th fret on an open string, which gives you a rather hollow sounding note.  The midway point of the string is where you would touch it with your fingertip to get a natural or artificial harmonic as well.

So I'm curious to know whether plucking the string at the middle of its length, whether open or fretted, enhances the octave effect.  If so, then your playing technique would want to adapt to this knowledge for best results!

[Mark Hammer]

Think of octave doublers as having attention deficit.  When you hand them harmonically complex signals, they feed you back more nonsense than mission-accomplished.  Feed them more fundamental than harmonics (what you get once you move up the fingerboard), and you get more mission-accomplished and less distracting nonsense.  You get to hear the octave because there's less other stuff to get in the way, either electronically or aurally.

We tend to forget how many circuits come from analog synthesizer origins, which in turn come from basic pure oscillator experiments from 60 years ago (or longer).  "Folding over" a waveform to get doubling is great....if the waveform being folded over is a pure steady-state sine wave generated by an oscillator.  If it's a time-varying, harmonically complex, amplitude-shifting signal like a guitar....well, the circuitry doesn't quite anticipate that so much.

[Digital Larry]

Think of octave doublers as having attention deficit.  When you hand them harmonically complex signals, they feed you back more nonsense than mission-accomplished.  Feed them more fundamental than harmonics (what you get once you move up the fingerboard), and you get more mission-accomplished and less distracting nonsense.  You get to hear the octave because there's less other stuff to get in the way, either electronically or aurally.

I've done a fair amount of experimentation recently in the DSP realm with ring modulators and to a smaller extent the "octave fuzz" rectifier.  And I can tell you with absolute certainty that a ring modulator on a guitar totally comes to life when the signal has most of the highs cut out.  I routinely run my guitar signal through a state variable filter with low, band and high-pass outputs.  The low goes to a ring modulator, and the other two go to whatever variety of things I feel like creating.  It is so flexible that #1 I think I've just scratched the surface of the possibilities and #2 I can barely stand the thought of building a fixed function circuit.  Please don't throw me down the well with those zombies.

But back to the original question, Joe Gore claims there is an octave fuzz "sweet spot" around the 7th fret which implies that going higher up the neck doesn't make it better.  Anyone agree/disagree/want a beer to think it over?

[Mark Hammer]

I think Joe is right, and more right for short-scale guitars.  The higher up you go, the stiffer the vibrating portion of the string, and the less harmonic content.