Envelope Fuzz

[aChorusofJays]

I've got an idea for my second build, but I wanted to see if anyone had tried anything like it before.

Basically, the idea is for a Fuzz pedal with a 'swell' setting. So, like with an envelope filter, when you hit a power chord, it gradually builds the Fuzz' gain into the signal. What I'm wondering is if I'm looking for something that will combine a Fuzz and Envelope-Filter circuit (or even a Fuzz and Compression circuit)? Or is what I'm describing possible just by having both pedals?

Am I being dumb or is this a cool idea? Thanks in advance!

[Mark Hammer]

Interesting idea.  Not exactly the same thing, but certainly in that samecorner of the forest, the Gretsch Controfuzz makes interesting use of the "swell" idea.  You can see the schematic here: http://www.generalguitargadgets.com/pdf/ggg_controfuzz.pdf

Where it differs from yours is that it has absolutely NO envelope detection.  Rather, what it does is make constructive use of the naturally occurring decay properties of a clean note vs a heavily clipped one.  In the schematic, you can see that, after the input cap, the signal goes to the noninverting (+) input of each of those two op-amps.

The first/leftmost op-amp provides juuuuuuuuuuuust a bit of clipping  by applying a gain of x2200 and then passing the signal by a pair of 1N4001 diodes to ground.  That signal is seriously attenuated down to a more realistic level by R6 and the 10k pot and is then fed to the inverting (-) input of the second op-amp, to be combined with the clean signal.

Now here's the thing.  Normal guitar strings have a big initial transient peak, and then tend to die out pretty quickly (faster for some instruments than for others).  A signal as heavily clipped as what shows up at the wiper of PT1 lasts a loooooong time.  Much longer than the clean tone.  Because of the way they are combined, what you end up hearing is the clean tone initially (fuzz is largely suppressed), followed by a fuzz tone that gradually swells as the clean disappears.

I gather it got the name Controfuzz because the normal behaviour of fuzzes is to start out really nasty (in response to the initial transient peak) and then simmer down shortly thereafter.  This one operates opposite to that.  While not exactly what you are trying to do, it comes awfully close.

One final note.  The reverse-fuzz effect relies principally on the relative balance of the two signals (clean and dirty).  This is why that 220k resistor is there before the first pot; to bring the fuzz signal down to a useful level.  If the 220k resistor is shunted by, say, a 47k resistor that will bring the level up hard, the reverse effect disappears, and the unit becomes simply a normal diode clipper.  Given how much gain is there, I would recommend that a capacitor be put in parallel with R3, R8, and the diodes to tame the sizzle beast.  For R3, try 330-470pf.  For R8, go with 100pf.  From that point, you can decide what you want to stick in parallel with the diodes.

[aChorusofJays]

Hey Mark,

Thanks for the quick reply! Interesting effect, it's amazing how many different products have come out putting little tweaks on the same theme.

I think what I'm looking for is a lot more control over a dynamic gain. Let me give a scenario:

Playing some rock distortion with power chords, and then switching on the Envelope/Fuzz for some staccato parts, and then one sustained final attack. The last attack would hopefully go from the simple distorted tone, to gradually more fuzz (kind of like blowing a fuse on an amp except without the volume loss).

Then, I'd like to have controls for time and volume on the pedal as well. So, it takes anywhere from 0.2-2.0 seconds for the fuzz to swell to the max by the time control, and the volume control would help the gain to increase at the playing volume, or increase, or decrease (again, dieing amp...).

I'm very new to this, so I'm probably dreaming up something that's more than I can chew, but it seems like something I would use!

[Mark Hammer]

Well, again, keep in mind that under natural circumstances, fuzz intensity declines fairly quickly with conventional pedals unless massive amounts of gain are applied.  If the intent is to gradually increae fuzz intensity over a period of up to a second or more, you will be swimming against a strong current unless you do something to maintain a constant high average level over that period. 

There is also the matter of the envelope extractor.  You can't extract an envelope from an unchanging signal, so you'd need to a) tap your envelope from the unprocessed signal, and b) provide some means to extend the life and level-stability of the signal after the point where the envelope is extracted so that there is something to apply the envelope to.

As I am fond of reminding people, effects and patches that work great for keyboard or synth can very often not work so great for guitar simply because guitar signal is unstable and has a short lifespan.

I encourage you to build the Controfuzz in the meantime, if only to get a feel for what your eventual end-product might sound like.  It is only a 60-minute perfboard build (if that), so well worth the time investment.

[aChorusofJays]

That's a good point about the decay. So maybe instead of an Envelope/Fuzz, I'm thinking more of a Fuzz/Compressor. Something to sustain the natural note long enough for the clipping to smash the signal in 1-2 seconds. The thing I don't care for on the ControFuzz is the way the signal is split. I'm looking to build something noisier than that. Well, I've got some things to look into and learn, maybe I'll plan on building a compressor first, and leave the combo box to another time.