Fuzz Face Q1's collector resistor

[gigimarga]

Hello,

I've built a couple of Fuzz Faces with lowered resitors for Q1's collector (as i obtained using Analog Alchemy's calculator).
These days i had the chance that a very experienced guitarist (and with an excellent setup...) to test them and another with 33K resistor.

His conclusion for the ones which have the modified resistors was very strange for me (he had no ideea about my mods): "Sounds good man, but no Fuzz Face sound here!"

For the one with 33K resistor (and the same transistors as one modified) he said: "That's a Fuzz Face sound!"

I used the calculator because some of my Fuzz Face clones sounded gated until i lowered the 33K resistor...but what's the solution?

Always to put a 33K resistor?
Can i use a trimpot? If yes, which must to be the voltage on Q1's collector?

Tonight i've built a Fuzz Face using two MPSA13 and the 33K resistor...i biased Q2 at 4.5V...i've expected to have a very loud Fuzz Face, but i had an almost BC107/108/109 sounding one...and it was a little gated too...

Thx a lot!!!

[petemoore]

Can i use a trimpot?
  Just don't tell anyone...
  If yes, which must to be the voltage on Q1's collector?
  Something like 1.14v, er that's what I always got close to.
  Smart-a-sanswer would be whatever sounds great.
  And it needs to be exactly the same voltage as Q2's base !

[gigimarga]

Thx a lot Peter for your answer!

I promise not to post anywhere and anytime your trick about the trimpot...
In some circumstances I hate the answer "whatever sounds great" because what sounds good on my setup (including my poor playing...) can sound worst or better on another setup...but never the same 

A couple of days ago I tested best of my DIY stompboxes on a professional setup (Buddha/Fuchs/Sound City amps, original Gibson Les Paul/Fender guitars and a very good guitar player...) and i have some unwanted surprises: with the Gibsons almost all stompboxes sounds muddy or really bad due to the higher level of the humbuckers i thought (i have a cheap Squier...)...some of my boosters have a lot of noise (Omega and Java Keeley Boost...i used batteries...only AMZ Mosfet Booster sounded great)...some Fuzz Faces sounded gated...Maestro FZ-1S sounded like crap (on my setup it sounds good, excepting that it has almost no sustain...but i understood that's a well known problem of it)...thx God that almost all my Tonebenders sounded great...and Fuzz Jade sounded amazing...so that's the reason for that i hate "biasing by ear"  ...ALL the stompboxes souned good on my setup, of course!

And in the last...GOOD NEWS: after a couple of hours of strong brainstorming and mighty handworking your advice was carried on: i had the same voltages on Q1's collector and on Q2's base  !!!

[23]

just to put in 2 cents, but isn't it your set up that matters?
unless your selling 'em

[gigimarga]

You're right "23"...my setup matters mainly...it was just a curiosity for me...i hope that in a couple of years i will buy for me some professional setup (a David Gilmour like HIWATT amp, one good Fender and one good Gibson...)...in this case i don't want to lose my nights to build stompboxes that i will can not use in the future

[23]

True, True, just drag a pedal board into a shop and say lets play
My BSIAB 2 sounds killer with an LP into my Marsh plexi, but like sh*t into my VHT set up clean with an LP....    hey by the way IM havin a hard time finding an OD i like with a strat (new to the strat world) and im not a fan of the TS, got any suggestions?

[mac]

Much is said about Q2 collector voltage. Q1 voltage must be within a very narrow zone of about 0.2v to sound better, unlike Q2.
My Ge clone has a 22k at Q1 (AC121: 90, 120ua), Vc1=0.5v. A 33k was too much for that leakage. After experimenting with a lot of different leakage transistors I suspect that the original bias are intended for a 50ua Ge IIRC. Most Toshibas I have bias very close to 0.6v and 4.5v with the std resistors.
The TB MKII is more gated since it uses a 100k. Put a leaky Ge and it won't bias, unless you decrease the 100k to 47k or so.
Same thing for Si. I do not remember Vc1 in my Si clone but it is close to pete's suggested value.

mac

[gigimarga]

Thx a lot mac...one of my Ge clone (with BCY40)  sounded gated until i biased Q1 at petemoore 's suggested value...and a Si clone sounds good at 1.5-1.6V (with BC108).

The clone that used two MPSA13 i can not to bias, so i replaced the first MPSA13 with an OC43, biased in a moment and have now another Fuzz Face

Tonight i want to do one clone using 2 Si/Ge very low gain (about 40-50) variant

By the way, which is the "gainest" variant of Fuzz Face that you know?

[idlechatterbox]

By the way, which is the "gainest" variant of Fuzz Face that you know?

When I was experimenting with mine (silicon version), the "gainest" I could find were some old 1681 trannies. They were suprisingly quiet in terms of hiss/hum/buzz, but the pedal went from no effect to all-out distortion if you cranked the gain knob at all. 

[gigimarga]

I never heard about these trannies

[mac]

I do not like high gain trannies in a FF. They work but too much gain for my ears. Get some BDxxx (subclass 10), 2n2369a, 2n3903, etc and compare it to a 2n5088, bc549C, mpsa18 version.

A mpsa13 needs a smaller resistor at Q2 collector than a non-darlington transistor.

mac

[brett]

Hi
for a high-gain fuzzface, try an MPSA18 rather than the 13.  (Though many people have tried the high-gain thing and almost everyone dislikes it). The circuit is not designed for 4 transistors (each MPSA13 has two transistors in it)
Most importantly, check out RG's "Technology of the fuzzface" at geofex.com.
cheers

[gigimarga]

Thx all for your answers.
I can't find MPSA18 here. Can you tell me a good sub for it?

[mac]

Try A BC550C or 2N5089. The first is about 500, maybe a little lower than a MPSA18, but I do no think it will make any difference.

mac

[gigimarga]

Thx...i will try to build tonigh a Dunlop JH Fuzz Face