Having testing a few ac128 i have had for a while, one reads 100ua leakage and 100hfe (taking into account leakage) the rest are too leaky and a couple at at 100ua leakage and 50hfe (taking into account leakage)
Clearly these are incorrect for the circuit as it stands which requires 90hef Q1 and 120hfeQ2. But is possible within the gain of the transistors i have available to  replace the bias resistors on the collectors with trimpots and say a 1k resistor in series with each one. Would there be enough latitude for correcting bias to produce something usable.
Or am I pissing into the wind and should just sling the low uns' out !
(The FF test bed does sound crap as is)

It's whatever works. 50hfe is certainly not "incorrect" as the NKTs used in vintage fuzz faces were mostly low gain devices. Much higher gain transistors can also work in this circuit, Dallas Arbiter used BC108Cs from 1969 on.
Use whatever sounds good.

it is irresponsible to "sling" germanium, no matter how low gain. if you have 2x 50hfe, put em in a darlington. 2x 50hfe and a leaky higher gain = mkIII tonebender. more leak means more earthquake.

I'll keep them for a tone bender then!

BTW How do apply a darlington pair into a fuzz face - I thought that circuit is a darlington pair?

I would not sling them theres plenty of designs that include low gain Ge transistors.
In fact theres a thread called Christmas present that does just this from contributor Mac. this very week.
Whats more is you can use them in the place of diodes in a feedback loop in distortion circuits.

fuzz face is a feedback pair, it may have other names, some can't be printed in polite company. first 2 transistors in the mkIII form a darlington pair.

smallbear has the "oh my darlington" somewhere hereabouts, you can even make a bazz fuss type thing.

At the top of the page note "links"
from one of the links, look at the fuzz-face part
http://www.diystompboxes.com/analogalchemy/emh/emh.html
It is a good idea to look at the "links" and "schematics" and the other links at the top of the page.

Hi
That is an excellent site (if the calculator is accurate and I'm sure it is).  -  Thank you

A few questions please

a)I assume the "beta" value must mean gain as HFE?
b)I noticed that always R2 and R3 remain constant even if changes are made to Q2?
c)Also would there be any reason to alter R4?

Quote from: jimmyandrex on December 28, 2013, 01:08:33 PM
Hi
That is an excellent site (if the calculator is accurate and I'm sure it is).  -  Thank you

A few questions please

a)I assume the "beta" value must mean gain as HFE?
b)I noticed that always R2 and R3 remain constant even if changes are made to Q2?
c)Also would there be any reason to alter R4?

a) y
b) This calculator lets you plug in some values, and it will pick the right R1 to bias the circuit correctly. even though it is most common to bias with r2, many use r1 since it will not change the tone as much. also, if you build a tb mkII, that's the way to go.
c) every resistor is worth experimenting with. a breadboard is your best friend.

Why mess with the resistors at all? I bet it sounds awesome with two of the transistors in the 50hfe range..

Quote from: Electric Warrior on December 28, 2013, 04:18:43 PM
Why mess with the resistors at all? I bet it sounds awesome with two of the transistors in the 50hfe range..

+1

The 80-110 recommendations for the HFEs of the transistors in the Fuzz Face have been taken as gospel because of RG's article. Ignore those numbers. Too many people take these numbers as set in stone when they are far from it. You can get an awesome sounding Fuzz Face with transistors well out of that range with devices that are much higher and/or lower and in different combinations. The most respected builders on the planet do not stick with "the gospel" in their work. Dito for the leakage numbers. You certainly use transistors well over the 100uA mark as well. That said, keeping Q1 under 200uA of leakage is a good idea. Q2 is much more forgiving.

Quote from: Electric Warrior on December 28, 2013, 04:18:43 PM
Why mess with the resistors at all? I bet it sounds awesome with two of the transistors in the 50hfe range..

Because that's how a newbie will learn what effects what in a circuit.

Is the "sundial" on the "sunface" a bias pot?

my advice? get some sockets, and experiment to see what sounds best to you. it's all about tone, not numbers.

i just plug stuff in until it sounds good, and i would reccomend against going much bigger than 47r for e resistors in a FF.

bigger resistors will change the tone.

bias trimmers work well. i like one on each transistor. i pay no attention to my meter, i plug in the transistors, and play with the bias til it sounds ok then play with thru it a bit for a while to see if it changes.

never really looked at a sunface, but yah, probably so you can play with the bias a little.

"i would recommend against going much bigger than 47r for e resistors in a FF."

Not sure what you mean by this as 47r is only 47ohms?

it is indeed r for ohms, although usually "R". and we replace the decimal point with the multiplier often, to prevent/reduce "printing errors".

so 4700R = 4.7k ohms = 4k7

2,200pF = 2.2nF = 2n2 = 0.0022uF. you can see why we no longer use the leading 0 notation.

in a grounded emitter, it's a short circuit to ground that for all intents autobiases the transistor for ya, similar to a cathode biased tube circuit (while being completely different for reasons i'm not gonna get into here). then all ya gotta worry about is feeding input into the base, and taking the output from the collector.

any time you have the gain maxed out, you're gonna find noise, and a lot of it in some cases.

if you stick a resistor between e and ground, you float the transistor...it has a resistance to ground that helps to turn it down a little.

in a tube amp, you may see a 1.5-3.3k cathode resistor, that's bypassed with a big ass cap, usually around 22u or so... this helps stabilize the tube, helps determine the overall gain the tube is capable of, and the cap allows some feedback and strengthens the tone, lets some high end bleed thru

in a transistor in a grounded emitter circuit, what i've found is that a VERY small resistance (10 - 100 ohms max) between the emitter and ground seems to make the fuzzes more stable, less prone to rfi and hash noise....at the expense of a tiny amount of the overall gain at hand.  so...

some peeps put a 1k resistor in there.. to me, it's too much, mellows out the fuzz, some folks may like it.

so about 47r is a good spot where it knocks back the gain just a little but is still close enough to a short for all intents and purposes for the transistor to function well.
you usually won't even have to tune your collector resistors.

i know this is wrong from an EE standpoint, i'm just trying to explain what i've learned in practical experience smokin' pots and caps and pots and ics and tubes and pots and... pot 

now i know me saying SHORT may be wrong too, but old mr. k in high school, who told us all we were nothing but a bunch of f'n peckerheads always called any connection to ground a "short". 

i mean.. a short is the shortest path to ground, right?

anyways... try the resistor trick. i sometimes use 10r ones. it's noticeable mostly on a wart... just a little less crackle fizz noise... and no cabs

> i mean.. a short is the shortest path to ground, right?

No. Not always.

When electricity is "supposed to" go through something, but finds a short-cut around that thing, that's a Short.

Come in my cellar and throw a wrench across the two fat black wires. Neither is grounded (that's the white wire). You still get a Dead Short across 250V, will melt your wrench and throw the hot steel in your face.

In this case the electricity from one black lead is supposed to go *through* the lights and heaters in my house then out the other black lead. Short-cut to the other black lead, that's a Short.

Take the battery out of your car, insulate it from "ground" on a plastic patio-table or thick glass slab, and put a (new) wrench across its terminals. Golly, another Dead Short. Didn't go through the starter, radio, etc. (Another ruined wrench, but slightly less molten steel thrown.)

In a FuzzFace, put a glop of solder base to collector one transistor. Neither lead is Ground. There's no big ARC, no molten wrench, but no sound neither. Electricity did not go through the collector-base area of the transistor. That's a common though un-popular type of Short.

but.... isn't one terminal still for all intents "ground"?

ground is 0 volts, postive is whatever postive voltage is, negative negative...
i see your point,

but for there to be a circuit, you have to have a voltage and a not voltage, don't you?

in order for it to be a circuit, current needs to flow from point a to point b... if there's no load, that was what mr. k told us was a short circuit...granted, i only took
his class for one marking period....

but in the case of the 220, you've gotta 440 volt difference being..... ahhh..... gotcha.

point noted, thanks!!

in the battery's case, i could make the claim still kinda... but not with a 220v line, which i assume would be 220v+, 220v- and 0 between them?

thanks paul!! i learned something new today.