fuzz theory: achieving sustain without losing treble??

[kat]

hi everyone.  This community is an awesome resource that I have been mining as I've been ramping up my pedal-building addiction, so a huge thanks.

I think I have a reasonable grasp on the basics of "fuzz theory" but before taking my next steps I would love to have my knowledge tested and augmented a bit.  The thing I am currently trying to do is build a "perfect fuzz" for a friend.  His idea of "perfect fuzz" involves fuzz-face-like sustain and harmonic richness but with more treble bite so it doesn't get muddy or lost in the mix, especially when played with the drive rolled off a tad so it's not at its most intense. 

So, I think that aspects of his request are in direct conflict (if I understand this all correctly).  You get the crazy sustain with a fuzz face because of its low input impedance, right?  That is, that it's loading the guitar a lot and capable of amplifying the tiniest signals.  At the same time, that loading means you lose some of the high end.  So I know there isn't a simple way to fix this problem, but I haven't personally played a gazillion fuzz pedals to know if some of the models out there manage to innovate their way around these issues or not. 

So first of all, I just want to confirm that I am understanding this correctly, and then what I would love to hear are some thoughts on reasonable compromises or smart design approaches that might get treble power, at least on the attack, combined with fuzz-face-like sustain. 

Some of the things I was considering are:
1) clean blend with something fuzz-face-like.... but I know it won't work to buffer the fuzz, and I don't know how well non-buffered blends end up working...
2) something more like a big muff with a clean blend added
3) something that involves a treble-boosted component of the signal added back in
4) something weirder?

Are there tried-and-true solutions to get what I'm looking for?  What's worth trying first? 

[thermionix]

The thing I am currently trying to do is build a "perfect fuzz" for a friend.  His idea of "perfect fuzz" involves fuzz-face-like sustain and harmonic richness but with more treble bite so it doesn't get muddy or lost in the mix, especially when played with the drive rolled off a tad so it's not at its most intense.

I would recommend trying a smaller input cap.  Like much smaller.  Stock for a Fuzz Face is 2.2uF, see what you think at .022uF or so.

Another option is to put a buffer in front.  That can get real harsh real fast, though.

You get the crazy sustain with a fuzz face because of its low input impedance, right?

I would think it's more about the gain.  The muddy tone is more related to the low input impedance.

Just my $.02.  Others will be along with more/better suggestions.

[amptramp]

The sustain from a Fuzz Face comes from its non-linear amplification - it has relatively large gain at low signal levels but at higher levels, it does not respond to negative excursions of the signal due to the low bias on the input.

The low impedance does lose high frequencies if the Fuzz Face is directly connected to the guitar due to the inductance of the pickup.  Imagine the pickup as a voltage source in series with a resistance from 5,000 to 14,000 ohms and an inductance of 3 to 5 Henries.  As the frequency gets higher, the inductance acts as an additional resistance (with a phase shift because it is reactive) so with the low input impedance of the Fuzz Face, the treble level goes down.  This effect is known as tone-sucking.  But the original treble is replaced by harmonics generated by the Fuzz Face.  If you want the original treble to be there, add a buffer ahead of the Fuzz Face with a high input impedance.  However, some guitarists think it is blasphemy to put any buffer between the guitar and the Fuzz Face because you get interactions between the guitar harmonics which are not quite related by integer multiples to the fundamental and the harmonics generated by the Fuzz Face which are locked to integer multiples.

The low input impedance does not add to the sustain.  You could get a better sustain from a compressor with a high gain on the input.  The gain of the circuit varies inversely with the input level, so as the guitar string amplitude gradually decays, the compression level gets reduced and the signal at the output remains almost constant.  (Or just hold the guitar up to the speaker and drive the strings through mechanical impingement of sound on the strings.)

[Electric Warrior]

Try a 100k volume pot. It will cut down the bass significantly, resulting in a brighter sounding fuzz.

[kat]

Thanks for the input everyone who has responded so far! 

I've already tried lots of little tweaks to the FF circuit (including different input caps, thermionix, and different volume pots).  I'm definitely in the camp of thinking that it just doesn't sound good buffered, also, having tried that a couple of ways. 

The replies are helpful for fixing up how I think about the sustain.  I was obviously mixing this up a bit with the tone sucking issues.  Although it's also an empirical thing - I've played around with compressor circuits and nothing so far gives me that same endlessness.  So in my head I convinced myself that it made sense that the killer sustain with the fF might be impedance-related, but I hadn't thought it through very much!

So this discussion so far would lead me to think that I want a buffered, high-gain fuzz circuit that has some intrinsic compression to it. 

Does it make sense to be thinking more in terms of a big muff-style pedal?  I don't fully understand why a buffer works in the BMP but not with a FF, which probably relates to the integer harmonics comment from amptramp.  My friend uses a BMP and likes it but has similar gripes... that it gets muddy and/or the sustain isn't beefy enough, depending on the settings. 

Thanks a ton for all the ideas, again.

[merlinb]

Can't you just build a FF and put a treble boost after it? Like a Rangemaster or whatever?

[merlinb]

I don't fully understand why a buffer works in the BMP but not with a FF,

Because the FF is basically a shunt feedback amplifier, except it has no input resistor; the input resistor is formed by the guitar internal impedance itself. If you put a buffer in between (which has a very low output impedance) then your FF now effectively has a really small 'input resistor' so it's gain goes way up and its character is radically different from when the guitar was plugged in directly.  If you put a resistor between the buffer and the FF (10k to 50k) it sounds much better. (In fact just putting a variable resistor in front of the FF is perhaps the most useful mod you can do, buffer or no).

[kat]

Can't you just build a FF and put a treble boost after it? Like a Rangemaster or whatever?

This is not the same thing as what I am going for... yeah I can boost the high end of the fuzz (all the harmonics that the fuzz introduces), but it's not the same as the high-end frequencies that were part of the original signal from the guitar.  Those are suppressed because of the loading so there's not really any way to get them "back" once the signal has passed through the fuzz circuit. 

[Mark Hammer]

Always remember that:
1) all such devices operate by applying lots of gain to the input signal, so that it runs out of headroom;
2) the tone we seek comes out of harmonics added to the input signal as a result of that lack of headroom;
3) the harmonic content generated is always a function of the spectral content of the input signal;
4) plucked strings provide a rapidly-changing signal and lose a massive amount of their harmonic content within a few moments, post-pluck.

[kat]

Ok, so once again, thanks.  All this is helping me understand things better and hone in on what I might try out next.  A couple miscellaneous followups:

1) I tried out just sticking a variable resistor on the input of a FF.  I remember considering that a while back but actually I'd never tried it, so thanks for the reminder merlin.  The effect seems not totally different to my ear from rolling off the guitar volume a bit.  I know it actually *is* different, but the differences are subtle (or, quite possibly, just not noticeable playing at low volume, which is all I can get away with in the mornings!).  I'll continue to mess with this... it would be lovely if the silver bullet is something so easy.  Initial testing seems to show that the extra attenuation is at odds with wanting to keep killer sustain, so I don't know.

2) Mark, those are all good things to keep in mind for sure, but I think I had them all in mind already... the hard part is translating what I want into good ideas about how to achieve it (or if it's possible).

I want, overall, to have FF-like sustain and texture but adding in a bit more high-end clarity on the attack.  That's why I was leaning towards thinking about clean blend options, where I am (ideally) not modifying the signal that goes into the FF and it still creates a similar harmonic spectrum to what it normally would.  But then I am not sure what to try, because I am not sure if an un-buffered blend is going to be successful, or if the better route is to give up on the FF and look into other fuzz approaches that are happier buffered.  I know any and all options have been tested extensively by folks here, so I'm kind of asking a question about what people have done that worked well to get rich fuzz + long sustain + clarity on the attack.

Sorry to keep belaboring this... I'm a bit obsessed at this point...

[thermionix]

Initial testing seems to show that the extra attenuation is at odds with wanting to keep killer sustain, so I don't know.

I'm with you on that.

Just curious, how small have you gone experimenting with the input cap?  In my trials to achieve something like what I think you're going for, I liked 33n pretty well, but coupled with a larger output cap, like 47n.  10n (input) was way too thin.  Going over 47n started to get muddy again.

[kat]

Just curious, how small have you gone experimenting with the input cap? 

I think I did try 0.022uF but for whatever reason I ended up back at 2.2 just tuning it to my own preferences.   I always get weirdly dyslexic talking about LPF/HPF but lemme see if I can say this the right way around... the lower the input cap the higher the HPF cutoff, so the less bass you're allowing in.  yes?  so yeah, I can why that might be worth revisiting if I'm trying to change the tone balance, especially since this time I'm trying to build for someone else's ear not mine. 

[ashcat_lt]

The difference between distortion and fuzz is the frequency spectrum of what gets boosted and clipped.  You can get at least as much sustain out of a Rat as you can from an FF, and in fact you can get some really great "fuzzy" tones from a Rat when you roll the T pot on your guitar. 

Clean blend will start to make it sound more like a TS, but fuzzier.  Could be cool.  A passive split definitely will not work if one side of that split is an FF.  It can really only make the loading worse, and that loss of treble will affect both sides of the split.  You'll need a buffer - possibly two.  Then you'll need an LPF on the way to the FF side.  Series resistance alone won't do it.  A cap to ground after that series resistance could help.  Some people maintain that the inductance of the pickup is important, so prefer to add a "pickup simulator".  I personally think that's splitting hairs and won't have enough effect to notice, but...

[Transmogrifox]

My first thought would have been much smaller input cap and then compensate with a low-pass filter on the output if it's too "thin" sounding.  At some point you lose the gain at meaningful frequencies and no longer have the sustain.  There is a way to balance that, which is a multiple-order high pass filter (C-R-C-R...) with C series, and R to ground.  This gives a steeper filter slope which attenuates the lows more and preserves gain at high enough frequency to still get sustain.

Part of why you get muddy with a fuzz like this is an effect of intermodulation distortion.  The higher harmonics are riding on top of the lower harmonics.  When the lower harmonics push the circuit into clipping then the higher harmonics are basically gated.  The only time they have a chance to get through is when the signal is near zero crossings.  When the gain is high, this is essentially zero time.  The net effect is the higher frequencies are translated into  a bit of pulse-width modulation, which creates non-harmonic frequencies (fuzz).  It can sound good, but you certainly lose the transparent attack.

My intuition says to get what you're looking for a blend circuit is sounding like the right direction to take this.

On the topic of blend circuits: instead of blending with clean, try a mild overdrive, perhaps even a second FF circuit (possibly buffered) with a large-valued input resistor, small input capacitor and hard-wired at a lower gain (or at least crippled to a lower gain adjustment range).  I'll call this configuration the "double-barreled fuzz face".

It would be worth trying the second fuzz without the buffer first.  The buffer is mentioned only because I foresee some potential instability problems in the interaction between the 2 feedback circuits and the buffer decouples one of them (on that note it might be necessary to buffer both).  The reason it is worth trying is it might end up being a beautifully tuned interactive circuit that gives you a lot of complex flavor possibilities just by working the tone and volume knobs on the guitar.

The idea is you can get the FF on low gain sort of attack response blended with the following sustain.  With 2 FF circuits the phasing will be correct so you won't get as much likelihood of weird notch frequencies due to phase shift effects (or cancellation from being dead-out-of-phase).

The final idea would be a dynamic blend where the blend circuit rests more to the sustain (high gain fuzz) side and is driven with a fast attack to let the secondary circuit blend into the mix more on note onsets.  The only advantage I see to this is if the envelope detection circuit is set up like a 1-shot, so it attacks fast, but decays right away regardless of the input signal so it is always responding only to onset attacks. 

Then of course there is the multi-band distortion idea, which is similar to the blend circuit, but blends in a different distortion flavor on its own frequency band.  A really simple implementation would be the double-barreled FF with your lower gain (treble) end going into the treble leg of a BMP tone stack and the sustain side going into the bass side of the BMP tonestack.  That way you can further tune what you want hear from each side as you blend it.

I'm pretty sure a plain double-barreled FF will get you pretty close to where you want it to be.

[kat]

Oh, awesome, thank you for all of those ideas!  This bit...

Part of why you get muddy with a fuzz like this is an effect of intermodulation distortion.  The higher harmonics are riding on top of the lower harmonics.  When the lower harmonics push the circuit into clipping then the higher harmonics are basically gated.  The only time they have a chance to get through is when the signal is near zero crossings.  When the gain is high, this is essentially zero time.  The net effect is the higher frequencies are translated into  a bit of pulse-width modulation, which creates non-harmonic frequencies (fuzz).  It can sound good, but you certainly lose the transparent attack.

...was especially clear.  I don't know why I wasn't already thinking about it this way, but that makes tons-O-sense and helps me rethink a bit of what I am actually seeking here.

Your post has given me a lot to chew on and I feel distinctly more ready to start the next round of noodling.  I will report back at some point, and I welcome any further insights... especially if anybody has built anything along the lines discussed so far and can say what works and what doesn't.

[Ripdivot]

I have run a FF style pedal into a parallel fx loop blend pedal with a Klon or Tube Screamer type circuit in the loop and it sounds fantastic. I tried blending clean signal and didn't like it, I found that a mild overdrive sounded great!

[kaycee]

I run my FF with 150n input cap and 4n7 out cap, 100k pot, its very trebly. Can't help with the sustain much other than to suggest getting it from the amp? Or run a compressor after, which I don't like much myself...

[Mark Hammer]

Here's something that never really got its due: Bill Berardi's Fuzztain
Intriguing design whereby the LED halves of a pair of optoisolators are used for clipping, but the LDRs are used for compression and enhancing sustain.
http://www.diystompboxes.com/smfforum/index.php?topic=57923.msg450596#msg450596

[Plexi]

The 100k volume pot is the best mod that adds treble: but I depends a lot of what amp the FF are pushing.
It's good into a hot Marshall-like pre, not too god into a blackface super clean: super fizzy.

[cnspedalbuilder]

@Mark Hammer: that looks cool. do you know of any demos of the Fuzztain? I've seen demos of the Maestro Fuzztain but I think that might be different.