Fuzz cleanup

[Dreadneck]

This has been bugging me for a long time now..

What makes the fuzz face and the tone benders to clean up a lot better when rolling of guitar volume than muffs?

I would love to mod one of my muffs to get such nice clean ups.

[Vivek]

Which muffs have you got ?

[Steben]

Gain and input impedance.
Big muff has tons of gain and 2 clipping stages. This makes for very hard circuit to get clean.
The input impedance is just as crucial. A Fuzz Face has a very low input impedance. It "loads" the inductive guitar, forming a low pass filter. As soon as you start rolling off guitar volume this effect drastically changes given the fact the guitar becomes more and more resistive and less dominantly inductive. In other words: the lower frequencies get reduced more than the high frequencies. In a Big Muff this effect is futile which means rolling off volume means less gain on the first place, giving no advantage to the high frequencies.

To get the same effect, you need far less gain and some kind of very present "treble bleed". Or lower the input impedance of the Muff but that woudl cause a huge change in tone. Probably not pleasant.

[Big Monk]

This has been bugging me for a long time now..

What makes the fuzz face and the tone benders to clean up a lot better when rolling of guitar volume than muffs?

I would love to mod one of my muffs to get such nice clean ups.

In my experience, not all Fuzz Faces or Tonebenders clean up well. In fact, even the best examples of the Tonebender MK II only cleanup marginally well compare to a finely tuned Fuzz Face. In the case of these devices, tuning really is the main point here. I've found that having a pre-gain control and a trim pot on the collector of Q1 in a MK II can help balance the essential "Tonebender-ness" with near Fuzz Face levels of cleanup.

As stated above, the Big Muff just doesn't cleanup. It simply maintains the same tone but quieter. Some of the overall frequency response is changed when you turn down but the distortion and edge is still there.

[Vivek]

There are two concepts that are at loggerheads:

Great sustain = take any input signal from 2mvp till 2Vp and output almost exactly the same output wave shape and amplitude

Great dynamics = do different things to signals based on the amplitude of the signal (Or as I learnt from the post above, based on change in impedance of input due to guitar volume settings)

We can design / alter a pedal to be somewhere in the middle ie good mix of :

Fairly good sustain with fairly good dynamics.

Such a pedal would have better response to playing style and guitar volume control than a high gain pedal.


For a Muff, we need to drastically reduce the gain of the two stages that have the clipping diodes so that the dynamics and ability to "clean with volume knob" are increased . One method could be to add 47K "compliance resistors" in series with the diode sets. It might not remain a Muff after that surgical operation, but it will get you what you want.

[Steben]

There are two concepts that are at loggerheads:

Great sustain = take any input signal from 2mvp till 2Vp and output almost exactly the same output wave shape and amplitude

Great dynamics = do different things to signals based on the amplitude of the signal (Or as I learnt from the post above, based on change in impedance of input due to guitar volume settings)

We can design / alter a pedal to be somewhere in the middle ie good mix of :

Fairly good sustain with fairly good dynamics.

Such a pedal would have better response to playing style and guitar volume control than a high gain pedal.


For a Muff, we need to drastically reduce the gain of the two stages that have the clipping diodes so that the dynamics and ability to "clean with volume knob" are increased . One method could be to add 47K "compliance resistors" in series with the diode sets. It might not remain a Muff after that surgical operation, but it will get you what you want.

It will not give that "from sputtery fuzz to glassy clean" effect of a fuzz face.

[Vivek]

Any suggestions on what mods could be done on a BMP to increase its range ?

[Big Monk]

Any suggestions on what mods could be done on a BMP to increase its range ?

Range of what?

[Vivek]

Range between fuzziness with full volume control versus clean sound at low settings of guitar volume knob

[Big Monk]

Range between fuzziness with full volume control versus clean sound at low settings of guitar volume knob

It would cease being a Muff If you tried cleaning it up. It's just one of those things. You want Fuzz Face cleans? Or Tonebender "cleans"? Get one of those.

A Muff will never really clean up in any form. With that said, lower gain transistors will help. I recently built my "forever" Big Muff on the PedalPCB Muffin board using specially selected transistors from my stash. It's a Ram's Head with a switch to flatten out the mid scoop.

Now, it NEVER truly cleans up but retains the Muffiness when I turn down with less aggression.

It's just one of those things.

[radio]

Replacing the silicon diodes with leds could be a change in the right direction or just drop the diodes in the first clipping stage

[teemuk]

Or decrease stage gains. They are generic negative feedback circuits. Modifying the loops for lower gain is more effective than modifying the transistors for lower gain.

On that note, one reason why Fuzz Face "cleans up" is that it's also a negative feedback circuit AND the feedback ratio (and thetefore also stage's gain) is partially defined by the source impedance. Higher source impedance (e.g. guitar volume pot turned down) decreases gain of the whole circuit so you not only get attenuation from volume control but also overall decrease in gain.

If you buffer the input the source impedance becomes fixed and you loose this effect.

Yes, Big Muff does this to a degree too, but the effect is in only one of gain stages out of four (while fuzz face has only a single gain stage inside global feedback loop). In addition, big muff features a large-ish series resistor in input that levels out variations in source impedance.

[Vivek]

On that note, one reason why Fuzz Face "cleans up" is that it's also a negative feedback circuit AND the feedback ratio (and thetefore also stage's gain) is partially defined by the source impedance. Higher source impedance (e.g. guitar volume pot turned down) decreases gain of the whole circuit so you not only get attenuation from volume control but also overall decrease in gain.

A Fuzz Face has a very low input impedance. It "loads" the inductive guitar, forming a low pass filter. As soon as you start rolling off guitar volume this effect drastically changes given the fact the guitar becomes more and more resistive and less dominantly inductive. In other words: the lower frequencies get reduced more than the high frequencies.

Thank you dear Gurus, for this insight.

What is the best SPICE model/values for Guitar pickup to simulate the feature of guitar volume control being part of the gain determining network ?

Will this be OK ?

[pacealot]

+1 to the multiple gain stage issue. The only way I've been able to "fake it" with a Muff is by putting a fairly heavy treble bleed cap across the sustain pot, as I've found that removing some of the low end into a less heavy fuzz helps emulate some of the natural low frequency roll-off of the FF that Steben described. In a Muff it makes the low sustain settings usable for me, as I've never enjoyed the dull stock tone when rolling that pot below around 75% or so. But it wouldn't solve the issue of trying to get it to clean up from your guitar volume (not unless you went down the rabbithole of rigging your guitars with an equally heavy treble bleed circuit — that was a bridge too far for me). And it still doesn't sound anything like a cleaned-up FF — it just gives a subjectively "better" lower-gain tone to the Muff, but it still sounds like a Muff, as everyone else has said.

The only other semi-effective way I've negotiated the issue of making one fuzz that both cleans up at one extreme and also gives me full saturation and sustain at the other has been doing the 2-stage/3-stage Fuzz Face/Mk II thing with a footswitchable first gain stage; so in 2-tranny (FF) mode, it's optimised for good cleaner tones (for me that means heavier high-pass filtering at the input cap, closer to that of an Italian Vox Tone Bender), and in 3-tranny Mk II/Supa Fuzz mode, it just does everything at maximum...