Its official. I hate Fuzzfaces.

[Outlaws]

Try the improved fuzz face "the Tonebender MKII" you will never go back !!!

Will do.  I was reading about that today actually.  It doesn't say "face" so its all good.   :lol:  :lol:  :lol:  :lol:

[Paul Marossy]

Fuzz Faces wont be for everyone, but most agree, a properly set up fuzz face sounds beautiful...

I agree. The Boutique Fuzz Face is a great sounding circuit. It still is somewhat tempermental, but a Si/Ge combo can sound really good and minimize the variability in the tone due to temperature, etc.

[petemoore]

3V on Q2C...what to do...
 Putting discussions of FF dummness aside, for a moment, getting a biased FF should preclude bias against a FF.

[stm]

Putting discussions of FF dummness aside, for a moment, getting a biased FF should preclude bias against a FF.

:lol:

According to my latest experience with the FF, I can add the following:

1) I liked the voicing of the Axis Silicon FF

2) I coulnd't get the so looked 70 and 130 hfe trannies; instead I ended up using two pairs of hfe 180-190 BD139's, where a 47k resistor joining the bases of the first pair gave hfe 70, and a 68k resistor joining the bases of the second pair gave hfe 125. I must say the resistors I calculated initially were around 22k and 30k respectively, but after I mounted the circuit and trimmed for 4.5V at the 2nd collector, I remeasured the effective hfe's and adjusted the resistors to the 47k and 68k values.

3) I couldn't get the FF to clean up gradually and nicely. Instead it changes from fuzzy to clean quite abruptly. The fuzz sound however is a keeper for me, especially for lead playing. Very different from opamp based clippers, so it is good in its own.

4) I still have to try methodically different collector bias and the effect on the "volume cleanup". In particular, I intend to try 4, 4.5, 5, 5.5 and 6V bias to see the effect.

5) I will try also the diode in series with the emitter of Q2.

6) I did run a sim with the BD139 devices, and funny enough, the 47k and 68k resistors in the simulation produced the very same 70 and 125 compound hfe's. This encouraged me to try the emitter diode on the simulation, and then some Ge diodes, one on each emitter. This required some rebiasing to obtain 5V at collector of C2, but interestingly enough, the edges of the upper part of the output seem to be more rounded!  I'm eager to get home to try this out in and hear how it sounds.

7) I tried also on my current prototyped circuit some stock 2N3904 transistors and BD139's as well, all of them with hfe in the 180-195 range, and the noise increased dramatically and there was some squealing which I could only eliminate by lowering the gain pot of the FF. So regarding to Outlaws and RDV complain on noise, maybe the problem has to do with excess gain. In fact, my sim shows when using stock BD139 trannies gain is near 75dB (5600 times), which is as much as the meanest high gain pedal you can imagine!.

This is all for now,

Regards,

STM

[Outlaws]

Just breadboarded a SiliFace2 and love it.  

[object88]

So I've been doing a bit of reading in The Art Of Electronics, and the authors warn against any design which relies on the Hfe parameter of a transistor, since they're so varied from specimen to specimen.

Of course, I haven't figured out what a better design is.  Are there any designs which (or perhaps I should say-- which designs) aren't Hfe-dependant?  Or is Hfe just something that we go with, since we (in a DIY setting) can hand-pick transistors?

I don't know enough to even know if I'm asking a coherent question, so please, be gentle, and speak slowly, and use small words.  

[Triffid]

I would guess he is looking from a mass production point of view, in which he is probably right.  Doing it yourself or in small production really lets you hand pick components for the best sound.  Its just a matter of patience and attention to detail.

[Peter Snowberg]

Are there any designs which (or perhaps I should say-- which designs) aren't Hfe-dependant?  Or is Hfe just something that we go with, since we (in a DIY setting) can hand-pick transistors?

Excellent question!

The way to get a stable amount of gain is to make the circuit more complex so that the transistors don't define the gain structure. The standard way to do this is to use a negative feedback signal. That allows you to set the gain with the ratio of two resistors which are quite stable and much better tolerance than semiconductor devices.

I'm beating around the bush here... the above configuration is at the heart of the "operational amplifier" circuit.

In the fuzz face we're taking advantage of how that circuit stops working when pushed too far. That means that changing to a different circuit to control the gain is not really what we're after. We want the results we get when the gain just happens to 70 or 125 or whatever, we're not really after the gain it's self. It's much more than just the specification of gain.

[Pedal love]

Considering germanium hfe, help may be on the way

http://www.banzaieffects.com/parts/transist.htm

Check under selected ac128 trannys