Green Ringer Lowpass Filter Mod: a fresher, cleaner octave

[Processaurus]

Here's a mod for people who like how octave distortions clean up when you roll the tone knob on your guitar down, but maybe don't like fiddlin' with lots of knobs every time you want some sweet octave.



The new switch in the GGG green ringer schematic does two things: it engages a lowpass filter, and at the same time doubles the gain on the first stage, to make up for the losses in the filter.  If you want to adjust the gain in the filter mode, change the resistor's value beween the emitter of Q1 and SW2b.  Lower value = more gain.  I don't know what happens if it gets really low, though.  The cap values in the filter are set up to barely let the highest note on a guitar get through, in order to try and get a guitar note to be as sine wave-like as possible.  To make the cutoff frequency higher and let high high notes be louder, you can scale the capacitors in the filter smaller, like .01uf, .0068uf, and .001 uf.  For bass, doubling the cap values would be a good place to start, as well is increasing the circuits input capacitor.

This filter makes the octave effect even more pronounced, and sounds the most like an octave using neck pickups.  around the 12th fret it starts to sound really cartoony.  Sweet...  


Here's a good article on "clean" octave generation http://www.geocities.com/SunsetStrip/Studio/2987/octave.html

[B Tremblay]

Very nice job!  An elegant solution to well-known Green Ringer caveat.

I would make a small suggestion: redraw the schematic if you plan to have this posted publicly for any significant length of time.  I understand that it's easier to append JD's drawing, but you're better off creating a new document.  Leaving JD's copyright info in place (or erasing it) creates confusion and/or the appearance of impropriety.

[Mark Hammer]

Either that or arrange to have it served from GGG only.  I've submitted mods to his artwork that JD posts from his site.

Incidentally, VERY very nice work.  Thoughtful and well planned out.  Viewers should recognize and make note of the use of:

a) a 3-pole filter to REALLY clean up the high end
b) the inclusion of compensating boost to make up for the perceived (and actual) reduction in amplitude when the highs are removed
c) a humble DPDT toggle to transform the personality of the device and restore it

There is much that can be improved on for the "classic" phase-splitter rectifier octave unit.  This mines that territory well.

Once again, kudos.

[analogguru]

I would invest two additional 1 M resistors to ground to avoid switching po-noise.

One from the negative side of the 10µF to ground, and another one from the 3 caps (switch-side) to ground.

analogguru

[seanm]

Very nice job!  An elegant solution to well-known Green Ringer caveat.

I would make a small suggestion: redraw the schematic if you plan to have this posted publicly for any significant length of time.  I understand that it's easier to append JD's drawing, but you're better off creating a new document.  Leaving JD's copyright info in place (or erasing it) creates confusion and/or the appearance of impropriety.

Or, I would cut out everything on the two sides of the  transistor and leave it as a circuit fragment.

[jsleep]

Hi Guys,

I posted this on the site (Green Ringer Project Page) with the text so that it will be easy to find.

I don't mind anyone using my schematics as a base to draw mods into it.  As long as you let me know, and give me the option to post it when you're done.  Most (soon all) of my diagrams will be stamped with annoying water marks.  Sorry guys, I had to do this.  If you want to draw some mods, just ask me first and I'll be glad to send you an "un-water-marked version for you to make your edits onto.  And also, please leave the copyright and date text as-is, just as Ben did on this one.  

Brian and Mark,  thanks for looking out for me ;-)

Thanks!
JD
http://www.generalguitargadgets.com/

[dacaumodo]

Any soundclips for this mod?

[soggybag]

I just built a Green Ringer with this mod and JC's null mod. I combined them together in the single build.

I'll post a picture of my combined mods schematic. But it's really pretty simple, the null mod just adds a trim pot and the filter just nestles in between the first and second transistors.

The filter mod sound good. The null mod let's fine tune the octave sound. My build sounded good and the octave was very pronounced with the filter switch on.

The null mod can be found at GGG:
http://www.generalguitargadgets.com/diagrams/green_ringer_null_mod_sc.gif

[sfr]

I'm looking more at this mod again today, and am very intrigued;

Something along the same idea should work with other octave-y pedals, like the scrambler and octavia?  the implementation might be different because of the circuit, but the idea should apply well in theory, I'd assume? 

I'll have to build another Ringer and try this out - it was one of the effects I was never a huge fan off and tossed off a while back. 

In the meantime, I'm wondering, how well something like this theory would work applied just prior to a pedal, rather than within the pedals first amplification stage?  For those of us with already-constructed octave type effects, (I have several) being able to box up a lowpass filter with a bit of amplification in it and toss it in front of whatever octave box I have, and switch the whole mess with an A/B box, would be interesting as far as an experiment.  (I'm sure if it works well, I'd want to alter whatever box I had hooked it up to.) I guess you'd have to be careful about the signal coming out of the amplification stage (I know some of my octave boxes get wierd when hit with a hard signal) but it should be easy enough to throw together.

[Processaurus]

I'm looking more at this mod again today, and am very intrigued;

Something along the same idea should work with other octave-y pedals, like the scrambler and octavia?  the implementation might be different because of the circuit, but the idea should apply well in theory, I'd assume? 

I'll have to build another Ringer and try this out - it was one of the effects I was never a huge fan off and tossed off a while back. 

In the meantime, I'm wondering, how well something like this theory would work applied just prior to a pedal, rather than within the pedals first amplification stage?  For those of us with already-constructed octave type effects, (I have several) being able to box up a lowpass filter with a bit of amplification in it and toss it in front of whatever octave box I have, and switch the whole mess with an A/B box, would be interesting as far as an experiment.  (I'm sure if it works well, I'd want to alter whatever box I had hooked it up to.) I guess you'd have to be careful about the signal coming out of the amplification stage (I know some of my octave boxes get weird when hit with a hard signal) but it should be easy enough to throw together.

This idea would probably make a great add on for any octavia, and would work the same in front of them.  The implementation here was just to save using a dual opamp circuit like the author of the article I linked to in the original post suggested (and where I got the idea in the first place, this is just a mutation).  You can do something like that with an opamp input stage, I bet you could get away with leaving the output buffer off.  It does need a buffer or gain stage between it and the guitar to behave consistently and not interact with the guitar electronics.  I'd give the input stage a gain of 2 or so, though, if you'd be wanting to turn it on and off, because the losses in the filter make it quieter, and the feeling when you hit a switch and somethings quieter is usually that it doesn't sound as good...

I guess to try it out if you have a couple octavias, a graphic EQ with the lows and mids turned all the way up and highs all the way down before it would give you an idea of the change in sound.

I just built a Green Ringer with this mod and JC's null mod. I combined them together in the single build.

The filter mod sound good. The null mod let's fine tune the octave sound. My build sounded good and the octave was very pronounced with the filter switch on.

Cool, thanks for the report, I did my build with the null mod too, but it was a switched trimpot instead of the external pot.  I didn't like the way the filter sounded with the subtler (unequal rectification) octave settings, it was just kinda muddy and lame.  Tried to think of a way to use a DPDT center off toggle to get filter--->octave, octave, and the subtler null setting, but thats just not gonna happen.  Maybe a 3 position rotary switch would be the way to go for the minimal controlist.

Right now I'm making a Foxx tone machine clone and am wondering if I can ride this trick some more by sticking it between the q1 collector and q2 base, but I don't get how the first stage is working with what looks like a notch filter in the feedback from the q2 emitter and q1 base, if anyone knows I'd be most grateful to hear how it works.

[sfr]

you know, it occurs to me to try this out with my Fuzz Face as well.  I have an old blue one, one of the Crest Audio re-issues, I believe, and I love the bell-like, singing tone that comes from rolling off the tone and switching to a neck p'up when using it. . .

I'm going to have to play with this this week.  Make something up in an external box, give it a go with a few different pedals and see what happens, and then work on hacking some of my old builds.  Like I don't  have enough on my plate.

(Edit, I just read the link in the original post here, where adding this to a fuzz was mentioned.  Duh.)

[petemoore]

  I'm wondering, how well something like this theory would work applied just prior to a pedal,
  I chose to do just that.
  Because I almost invariably like to have something on as boost or fuzz pre-GR, I put the filter section in front.
  I did adjust for a bit less HF rolloff, using sockets for 2 of the caps, then adjusted the gain as shown.
  I was using the GR as main Octave, but this and the null mod, these tailored it to better suit my uses for it...I mostly leave the settings with the mods switched in.
 

[Supernaut_]

Hi guys!

I want to build a Musikding Emerald Ring kit (a Green Ringer clone) with the JC Maillet null pot mod and the lowpass filter mod from the GGG diagram. I've got the null pot figured out but can't seem to get my head around the filter switch. So I'm guessing it should be a 2-way on-on DPDT toggle switch but how to wire the filter circuit to it? Does anybody have a simple wiring diagram on how to implement the filter switch, would be much appreciated. Cheers!

[Mark Hammer]

One half of the switch connects the caps to ground.  Because that introduces some passive loss, the other half of the switch connects the 10uf cap to ground at the same time.  The additional 6k2/10uf pair increase the gain of Q1.

What I do on mine to enhance the audibility of the octave is to make that second 6k2 resistor a 10k pot so that gain can be adjusted.  Because increasing gain also increases volume, I replace the 47k fixed resistor on the output with a 47k log pot as a volume control. 

Finally, I also run a back-to-back pair of diodes (any silicon type will do) to ground from the junction of C5 and the added volume pot.  After much examination of various octave-up designs, I noted that one of the elements in common was a similar diode pair.  They do provide a little bit of additional clipping but they are NOT essential to the fuzz sound.  What they do accomplish is a quick-and-dirty limiter function to hold the volume somewhat constant.  Why is this important?  Because every picked note starts out with way too much harmonic content and this tends to hide the octave (i.e., doubled fundamental).  That's why one is always encouraged to roll the highs off on the guitar, use the neck pickup, and pick higher up the neck, where there is less harmonic content.  That's also why the filter mod.  Since it takes a little while for the harmonics to settle down and let the doubled fundamental stick out, the string loses a bit of volume as well.  The diode pair keep the level somewhat steady so the octave isn't coming out of hiding when the note is dying out.  Although my own preference for D1/D2 is Schottky type, you don't want to make the output-level ceiling too low, so the added diode pair should be silicon.

Dino/digi2t hipped me to the idea of sticking a small resistor (a few hundred ohms at most) between the diodes and ground to reduce the clipping that the diodes might add, as well as a cap to ground in parallel to roll off any unwanted fizz.

The original Dan Armstrong design was bare-bones, as were pretty well all the plug-in boxes in that series.  No harm in bringing them up to what they could be.  My all-time favorite octave-up is the Foxx, but the suggested mods help the Ringer to be a much better octave-up.

[Supernaut_]

Thanks for the reply Mark, your expertise and willingness to help are greatly appreciated!

I'm also considering another approach, to keep the mods as simple as possible, ie. no additional switches, pots etc. In this case I'd add a 100 pF cap in parallel with the input resistor (here R13), replace D1 and D2 with Schottky diodes, and add, in parallel with the 47k R12, a combination of two 1N914 diodes in series with a 470R resistor. Does that sound about right, would you add something else?

Dino/digi2t hipped me to the idea of sticking a small resistor (a few hundred ohms at most) between the diodes and ground to reduce the clipping that the diodes might add, as well as a cap to ground in parallel to roll off any unwanted fizz.

Do you mean an additional cap parallel to the diode+diode+resistor combination? Does it have to be a polarized cap and what value would be suitable?

[Mark Hammer]

Yes. Diode pair to resistor to ground, and cap in parallel with the whole trio.  Something like 10nf is probably about right.  Feel free to season to taste, but that's a good place to start.

A 100pf cap in parallel with R13 isn't a bad idea, and can't hurt, but it won't be enough to accomplish what the filter mod does.  I will put in an enthusiastic plug for the variable gain mod on Q1.  The GGG drawing suggests it is an aspect of the filter mod, but the two don't have to go hand in hand.  JD shows it in the drawing as a way of compensating for the impact on signal level of the filter.  I use a 10k pot and 10uf cap on its own, to adjust gain, and find that can help me achieve more intense octaving, as well as reduce sensitivity below stock.  Actually, one can skip R4, replace it with a 10k pot, outside lugs going to the emitter and ground, and the 10uf cap going to ground from the wiper; essentially the same gain-control configuration one sees on many Fuzz Face derivatives.  If you want simplicity, I suppose you can always use a 10k trimmer, a 50k trimmer for the output volume, adjust Q1 gain for best octaving and output level for a suitable effect/bypass balance, and close up the box.

Personally, I wouldn't do it that way.  Many people tout the virtues of running an overdrive or distortion into an octave-up, so having some way to adjust Ringer input sensitivity (via Q1 gain) for boosted and unboosted inputs, as needed, strikes me as useful.  That said, it's your pedal, and your tonal goals.  I hope you can nail them.

[Supernaut_]

Brilliant info, many thanks! I intend to use the octave-up with a booster so maybe it's indeed better to have gain and vol. pots easily accessible.

So I'm guessing I can wire the gain pot eg. like this, lug 1 to emitter, lug 3 to gnd and the 10 uF cap between lugs 2 & 3. And the vol. pot; lug 1 to C5, lug 3 to gnd and jumper between lugs 2 & 3, correct?

[Mark Hammer]

Correct. Let us know if you like it.

[Supernaut_]

I'm still waiting for the parts to arrive so I can start the build, and was reading through this thread again. One more question comes to mind:

Finally, I also run a back-to-back pair of diodes (any silicon type will do) to ground from the junction of C5 and the added volume pot

By back-to-back, did you mean to wire the diodes in opposite directions, cathode sides facing outwards?

[Mark Hammer]

Correct.  That's why, when people see them in schematics for octave-up fuzzes, they mistakenly think that any fuzz is actually produced by them, rather than earlier parts of the circuit.