A few Fuzz Factory mods?

[mordechai]

Wondering if you'd share your thoughts on the following:

1. using a BC550 as Q1 (quiet, but higher gain) and thus reducing the value of the 220K resistor across the B/C to about 180K to compensate?

2. bringing down the 470R to 390R to tame the volume a bit and make the volume pot more usable?

3. adding a 1M in parallel with a 100p cap at the input stage to send RF interferences to GND and fight against potential popping?

4.  What are your favorite transistors for Q2/Q3? 

I know, this has been discussed to death, but there's SO much on this circuit it's difficult to cherrypick the useful bits without my wife leaving me...

[Mark Hammer]

Hi guy!

As what is essentially a highly tweaked Fuzz Face, many of the mods to the venerable FF likely apply here.  One of my faves is the manipulation of the feedback resistance between the emitter of Q2 (which is Q3 here) and base of Q1 (Q2 here).  The resistance used is one which will achieve pleasing fuzz.  Raising its value will interact with the Gain control to yield varieties of glitchiness  or spittiness.  Vex himself uses that manipulation on other pedals of his, like the Wooly Mammoth and Fuzzolo.

My own experience is that a continuous control is unlikely to be needed.  For my part, I think it better to use a temporary pot wired up, and identify two resistance values higher than stock that yield pleasing or usable tones, and then wire up a 3-position toggle to achieve the stock and two higher values by application of parallel resistance.  Frankly, with 5 knobs to tinker with, there is more than enough to play around with, without being distracted by yet another knob.  Best to limit the canvas and work within its limitations.

[mordechai]

Hi Mark, and thanks!

I've made "normal" fuzz faces with a trimpot instead of a fixed feedback resistor and it does let me tune the fuzz to interact with the different transistors I might use...but with a nutso beast like the fuzz factory it never occurred to me that this was something that could be used to creatively interact with the other over-the-top controls.  I will indeed give it a try!  I'm also going to use the "fat" switch option on that 100n between Q1 and Q2, and possibly also put a switch to go between an NPN germanium and the NPN silicon Q1 transistor. 

But what you do think about having the Q1 transistor be a BC550?  I like the idea of having a device know for being low-noise in that front position, but the additional gain it puts out does concern me...unless it's ultimately not so super consequential. 

I guess I could just socket that 220K resistor on Q1 and try out a 180K to see if that tames things a bit.  The same with the 470R...instead of messing with the in/out caps I think it might help give a bit more girth if the volume pot could be turned up a touch more without overdoing the output...

[thermionix]

But what you do think about having the Q1 transistor be a BC550?  I like the idea of having a device know for being low-noise in that front position, but the additional gain it puts out does concern me...unless it's ultimately not so super consequential.

Original Q1 is a 2N3904, right?  BC550A would probably average around the same hFE.  BC550B or C would be higher.  What germs (and gains) do you plan on using?  My next project to begin will be a Fuzz Factory, I've never built one, so I'm curious as well what people recommend for them.

[bassjunkie]

FYI https://www.diystompboxes.com/smfforum/index.php?topic=82385.0