Custom Fuzz-Face Calculator

[Joe Davisson]

http://www.diystompboxes.com/analogalchemy/emh/emh.html

Program automagically tries to design a Fuzz-Face for you, based on the Hfe values (& type) of your transistors. More options are coming...

[j0shua]

WHAT CAN I SAY JUST : EXELENT ONCE AGAIN!

[Alpha579]

good god joe,you truly are the man...

[Phorhas]

Joe, I can't thank you enough for all of your contributions to our community... your postings (here and on you own site) taught me alot and building your stuff has always been a pleasure.

Thank you.

[Peter Snowberg]

Very cool Joe!

[Paul Perry (Frostwave)]

Joe, is the answer in ohms or in Kohms?

[MartyMart]

Joe, is the answer in ohms or in Kohms?

FAB !!
Looks to me that its "Kohms" .......  ?

Marty

[Joe Davisson]

Sorry, it's K, I noted it on the page. At the moment it's probably better for all-silicon or hybrids. I tested "real" FF values (with the 1k pot) and it comes up with 39k for germanium (Hfe=100) transistors, which is close. Gain control selection is really the only other option needed, unless someone has other ideas.

Geofex has this nice circuit for getting a more accurate Hfe reading from germaniums:
http://www.geofex.com/Article_Folders/ffselect.htm

It's important to get the value close for Q1, since only a slight change can put it all out of whack. My multimeter reports 20-30% higher values which is enough to throw it off. So it's probably worth making the tester or getting transistors from someone who tests the values this way (I think Small Bear does).

[Joe Davisson]

Added the gain control selector, I think it's okay but will check it out more later.

[Marcos - Munky]

Cool!!! Thanks a lot.

[aron]

WOW!!!!!! COOL!

I needed this.

Aron

[sir_modulus]

Amazing Joe...Simply amazing...what would we do without you?!?!?!?!

(well, not have custom tapered pots for cheap, and not have custom fuzz faces for sure   )

Cheers!

Nish

[jmusser]

Wow, this is above and beyond the call of duty gentlemen. Nicely done!

[Joe Davisson]

Fixed a problem with mixing Ge/Si, and made it do all the resistors (except the 100k) to make up for volume differences, etc.

Also breadboarded a bunch of different combinations, and they seem to work/sound alright, so I guess it works. Have fun!

[Alpha579]

any chance of having a 5K drive pot available? like in hornet/lava rim ?    :wink:

[Fret Wire]

Real interesting Joe.  I think some people are scratching their heads because most everyone adjusts only Q2's collector when biasing a fuzz. Last nite I put a few different gain combos in my fuzz jig and gave your calculator a try. Battery voltage was 9.10v, and 1k was used for the gain pot/value.

TI 182505 (Ge):
gain/leakage:  Q1- 79/7, Q2- 133/35
calculated values:
R1- 47k
R2- 8.2k
R3- 470

Tested voltages:
Q1:  
E- 0.0
B- .124
C- .519

Q2:
E- .413
B- .513
C- 5.55

OC44 (Ge metal can):
gain/leakage:  Q1- 64/13, Q2- 88/17
calculated values:
R1- 60k
R2- 8.2k
R3- 470

tested voltages:
Q1:
E- 0.0
B- .107
C- .530

Q2:
E- .40
B- .52
C- 5.5

TI 2N404 (Ge):
gain/leakage: Q1- 172/23, Q2- 202/26
calculated values:
R1- 21k
R2- 8.2k
R3- 470

tested voltages:
Q1:
E- 0.0
B- .12
C- .544

Q2:
E- .43
B- .55
C- 5.55

I played them quickly last nite, and all sounded good. Good sustain, and cleaned up well with the guitar volume. These were pairs I had previously tested and were known to sound good.

As you can see, the voltages were pretty uniform. Especially considering that one pair was lower gain than normal, and one pair higher gain than normal. I usually bias by adjusting both Q1 and Q2's collector, getting identical voltages to the above, but I like to run about .5v less on Q2's collector. That usually gets a great sound. With some pairs, I've found they will bias up real nice by all three methods: adjusting only Q2, adjusting only Q1, or adjusting both. I didn't try any silicons, but if it works with Ge's, silicons will be a breeze.

Seems like when most people try to buy their own supplies of untested Ge's (picked thru leftovers), they usually get gains much lower or higher than the "magic range" of 70-130. Maybe later, I'll test more batches of low and high gain sets, and post them. Personally, I've found the higher than normal gains (Ge) to still sound great if they have low leakage.

ps- forgot the obvious dislcaimer: your ears are always the final judge.

[Joe Davisson]

Thanks for the testing info. The collector voltages look about 1v too high, probably the measured Hfe values are not compatible with the program for some reason. The program doesn't allow collector voltages below 4.25 or above 4.75. I'll look into getting compatible Hfe readings from germaniums.

Can you check your 1k pot with a DMM to make sure it's not actually 1.25k or 1.5k, just to weed out the possibility of that creating the higher collector voltages?

I updated the program a bit: added the 5k control, feedback-resistor adjustment, and got rid of the annoying drop-down selectors. There's also some default values in there now.

-Joe

[Fret Wire]

Your welcome Joe, I enjoy this kind of stuff I'll check my 1k pot later tonite when I get a chance.  My jig uses pots for all the resistor values, wired with 1/8" jacks to disconnect and measure. They were set (DMM) just before I tested. I was wondering about the Q2 5.5v collector voltages. I usually end up at 4.5v-5.0v. I just followed the calculator exactly to see how it would work. I'm impressed with how uniformly it got the voltages on three very different sets of trannys, gain wise.

[Gilles C]

Maybe that's what I need to make the one I build many years ago and never sounded good.

I need to do the maths...

[Fret Wire]

Joe, I checked my 1k pot, and it measures .910k. I'll test more tranny combo's tomorrow.