Differences between Axis Fuzz Si and Fuzz Face Si

[powerplayj]

Other than the slight difference in the schematic and the component values and transistor types, what are the tonal differences between the two?  I expect the Axis to retain a bit more high end and be a bit less saturated but, is there anything else significant?

Phillip (or others),
For this pedal, does the Axis title serve the purpose as the the name of your business or is it meant to reflect the tone of a particular Hendrix album?  


Thanks,

Jason

[phillip]

The Silicon Axis Face (not to be confused with the Roger Mayer "Axis Fuzz") is a lot smoother and warmer sounding than the regular Silicon Fuzz Face, which is characteristically nasty sounding.  It sounds almost exactly like the Germanium version by using low gain Silicon transistors with some tone shaping capacitors and some altered parts values.  You can also use higher gain transistors in the circuit for more fuzz.

The 100pF capacitor across the collector and base of Q2 should be Silver Mica...I need to make a note of that on the Axis Face Silicon page.  A ceramic capacitor will impart a "fizzy" sound...at least it did when I first prototyped the circuit.  Then I went on eBay and bought a bag of 100, 100pF 5% Silver Mica capacitors (fairly small ones) and once I replaced that ceramic capacitor with one, the fizzy sound went away.

The Axis Face is so named because of Axis Guitar Effects...nothing to do with the circuit sounding like a Hendrix album.

Hope this helps!
Phillip

[octafish]

Firstly, wow the forum is fast now!
Secondly the mods philip has made to the silicon FF do help control the silicon harshness. I haven't built one with the low gain transistors and I find that high gain silicon transistors in my example do not sound exactly like germs. However I did do some tweaking of values (I can never leave well enough alone) I can easily get a better sounding Si FF with phillips changes than with the standard circuit. The capacitor between the base and collector is (for me) the real magic part clearing up the harhness of the silicons. I used a larger 270pf ceramic in there IIRC, I'll have to get a few silver micas and revist  this one to see if they do make a difference I can hear. I'm pretty clotheared by the way so please don't take that personally phillip! I would also recommend checking out the EMH at http://www.diystompboxes.com/analogalchemy/index.html if you're thinking of making a NPN FF. I built a fuzzface using it recently for a friend and it was the first FF I have built that biased correctly without trimpots, cool.

[phillip]

Yep when you use higher gain Silicon transistors in the circuit it will lose that nice Germanium-replicating sound.  I used some BC108Bs and it definitely started to lose it, but once I put a 2N4400 in Q1 (hFE = 74) and a 2N2222 (hFE = 125) it almost perfectly matched my Germanium version of the Axis Face...the Silicon version was still a touch brighter and more dynamic and responsive.

Phillip