Modding the gain on the Q2 of a Fuzz Face

[MordechaiBenZev]

I've got a nice set of transistors for a fuzz face circuit, but Q2 is running a little high...about 200 Hfe.  I'd like to lower it to respond more like something around 140-150 Hfe, and I recall a post somewhere that putting a small value resistor (100-200R) between the emitter and GND can help with that. I'd appreciate anybody's suggestions regarding what value would probably do the trick here. 

[FSFX]

You may like to read this:

https://www.diystompboxes.com/smfforum/index.php?topic=52837.0

[Dormammu]

The circuit has a gain control knob.
And negative feedback resistor.
They determine the actual gain.
Just build a box.   

[Steben]

Depends on which type of transistor you are looking for.
Main stream silicon transistors are not expensive....

[Fancy Lime]

At this point, I think, it would be much easier to give useful advice if we had a schematic to refer to. There may be some ambiguity about which transistor is Q1 or Q2.

Andy

[MordechaiBenZev]

The circuit has a gain control knob.
And negative feedback resistor.
They determine the actual gain.
Just build a box.   

I have only one PCB (a reproduction of an original style fuzz face board) and don't want to futz too much with it!  Am I correct in understanding that increasing the value of the 100K resistor from the E of Q2 to the B of Q1 will tame the feedback signal a bit?  I seem to recall the Eric Johnson fuzz face using a 120K resistor there, which I think was to soften the feedback signal a bit with the hotter transistor in Q2...

[Fancy Lime]

The feedback resistor feeds a little bit of signal back from Q2 to Q1. But it is negative feedback, so smaller value, meaning more signal fed back, will make it tamer. Theoretically. However, the primary function of this resistor is to bias Q1. What value is "right" here, depends on the hfe values as well as the collector resistors of both transistors. If the resistor is too large or too small, you leave the Goldilocks Zone and get first more nasty, then sputtery and gated fuzz and finally no signal at all.

The problem with giving useful advice for concrete values of resistors in a Fuzz Face type circuit is that everything interacts with everything here. Lots. Trial and error is often the only way to find out what combination of components and values sounds good in these things. Do you have a breadboard?

Andy

[antonis]

I've got a nice set of transistors for a fuzz face circuit, but Q2 is running a little high...about 200 Hfe.  I'd like to lower it to respond more like something around 140-150 Hfe, and I recall a post somewhere that putting a small value resistor (100-200R) between the emitter and GND can help with that.

If only a single (or more) resistor(s) could alter/set particular BJT h_FE..

P.S.
A resistor between Emitter & GND alters STAGE gain..
(due to series feedback action, which has nothing to do with transistor DC current gain..)

[pinkjimiphoton]

I've got a nice set of transistors for a fuzz face circuit, but Q2 is running a little high...about 200 Hfe.  I'd like to lower it to respond more like something around 140-150 Hfe, and I recall a post somewhere that putting a small value resistor (100-200R) between the emitter and GND can help with that. I'd appreciate anybody's suggestions regarding what value would probably do the trick here.

that someone was likely me.
yes, putting a small resistance between e and g will work.
an hfe of 200,  somewhere around 47r to 100r should do the trick. go a bit bigger with q1 if ya need to drop the gain some.
in the skydog fuzz that bozo ripped me off with, its 100r for q1 and 47r for q2, with both of the mpsa06 reading around 220hfe.
yes, you can still do this where the fuzz pot is, just put it between the e and the top of the fuzz pot. accomplishes the same goal in the end.
if you put it after the pot, the pot won't turn all the way down.
if ya need the schematic, let me know.
Peace

[antonis]

Jim, should 2023 be enough to count your Fuzz variants..??

[pinkjimiphoton]

easy, lol. i am out of that game completely. i had enough....