Does anyone know if the last stage of this fuzz saturates or is clean?

[Esppse]

Hello,

Looking to build this Meat Grind fuzz from diyguitarpedals:

https://www.diyguitarpedals.com.au/shop/boms/Meat%20Grinder%20Fuzz.pdf

The volume is before the last 2N3904, so technically raising the output volume will yield dirty volume and distortion right?

I may add another last volume pot after it if this is the case.

I actually had come across this same dilemma when building an AMT B1 clone, where the last transistor is after the volume. I added a post volume and it really helps dial the tone because in the B1, that last stage does distort quite a bit.

[ElectricDruid]

I don't know, but the modification is easy to do. Since R28 is 100K, it can easily be replaced with another 100K pot like VR4 without any other changes. Which then gives that last stage "pre" and "post" volume controls.

Whether it actually distorts that last stage or not is going to depend on what the signal level is when it gets there. Given the use of low forward-voltage schottky 1N5817 diodes in the hard clipping part and that then being followed by a tone control which removes still more signal, I doubt it distorts. The diodes will put an upper limit on the volume that could be as low as +/-0.25V (just looked up some random datasheet for the 1N5817).

HTH

[GibsonGM]

Easier to breadboard it (for me), or sim it in LT Spice etc, than to do math    

As Tom said - the signal should be pretty well eaten up by the tone stack & schottky's, shouldn't be too hot going into the buffer. I'd just move the vol control if that's a problem.  Can't see why it would be, tho.

[Mark Hammer]

The circuit is a Superfuzz with a few added controls.  That's not a criticism, just a description.  It HAS to be given a different name, for simple legal reasons and to not misrepresent it AS a UNivox, or similar, product.

That said, the midscoop filter eats up a lot of signal, so a gain recovery stage after the volume pot is needed to provide acceptable output levels.  This is no different than the post-tonestack gain-recovery stage on a Big Muff, where the tonestack also eats-up/bleeds-off a lot of signal.  It merely raises the amplitude of whatever is coming from the volume pot wiper, without deliberately saturating.  Although I suppose "punishing" levels feeding it could be arranged, but the contrast with bypass level would be highly impractical.

The variable clipping is something that has been discussed here often, and frequently by me.  "Better" octave-up fuzzes will include a diode pair like that.  Why?  Guitar strings provide the most harmonic content during the pick attack.  Moments later, the string settles down and the note fundamental becomes a more prominent feature.  As such, the octave-up tends to get lost amidst the "harmonic haze", and only emerges as the note is held after all that doubled harmonic garbage has dropped to the background.  The problem is that, by that point, the string amplitude has also dropped, such that the octave is not as loud as one would like it to be, as it is emerging from hiding.  After all, one uses such an effect for the octave to appear deliberate, not an afterthought.

Consequently, several designs included a diode pair to provide quick and dirty peak limiting that would offer the illusion of somewhat constant volume, at the cost of a little more harmonic content.  If one lifts those diodes or inserts  resistance between them and ground, you'll find the distortion is still quite in evidence, and coming from earlier stages, NOT the diodes.  That's what led me to understand what their true role is.  Erik included the variable resistance control to adjust the peak limiting.  I doubt it needs to be as high a value as he shows (2k should be more than sufficient).  I would imagine the diode pair can become superfluous if one feeds the circuit an already compressed signal.  In that instance, Erik's added control allows one to subtract whatever additional clipping the diodes add, because the note will already maintain relatively constant volume

I've built a number of octave-up units, the Foxx being my favourite.  But I've built several Green Ringers, which normally lack such a diode pair.  I increased the gain of their input stage, to improve sensitivity, and added the diode pair, with a few hundred ohms between them and ground, and the difference in audibility of the octave is noticeable.  The original Dan Armstrong designs aimed for minimalism, sacrificing a bit of usability in the process.

All analog octave-up units need to "cling" to the note fundamental for a bit, in order for the octave up to bloom.

[Elektrojänis]

Depending on how you set the other controls (max. resistance on the tone and clip pots), it might be possible to make the last stage distort. However, the question I'd ask is does it change the sound in a desireable way?

I bet the other stages distort enough anyway, but there is only one way to find out what sounds best to you.

One thing to remember is that while a lot of controls and adjustability might seem good to have, too many controls might just get in the way in the end, especially if most of them are subtle. It might be better to make a pedal with less controls and then go on and build a next project that's different to add more options to your tonal palette.