High Hfe (400) fuzz

[andrea2127]

Hi, my uncle give me some bc108b/bc109b transistor with a high hfe of 300/400. Can i use it to build some fuzz pedal? an easy fuzz face for example? or there are other type of fuzz that i can build with this transistor? Thank you for your help.

[nocentelli]

fuzzface, tonebender mk 1.5 / aka fuzzface, vox distortion booster, tonebender mk 2, and the hot silicon are all of a similar design and will work ok with BC108/9. They would also do for a big muff. 

[andrea2127]

do i have to worry about the high level of Hfe? i've read online that good q1 q2 for fuzzface have hfe about 70/100 for q1 and 100/140. will it work the same also with the same schematics?

[Lily]

http://www.home-wrecker.com/sili-face.html
http://www.home-wrecker.com/sili-face2.html

One of these should work too. I've made the second one before and I liked it, although I do receive radio sometimes.

[nocentelli]

do i have to worry about the high level of Hfe? i've read online that good q1 q2 for fuzzface have hfe about 70/100 for q1 and 100/140. will it work the same also with the same schematics?

I wouldn't worry about it, just try it out. It will work, it may not sound exactly like the original someone's idea of a classic fuzzface, but you may well like it anyway. Recommendation about HFE, Q2 collector voltage etc are often fairly subjective.

[andrea2127]

Ok, guys! I'll try as soon as possibile. Thank you for your advice and for answer me. I think i will go for the fuzz face that seems to have a easy layout and less components. It's good to start with this one?i'm not so experienced about pedals. Thank you again.

[pinkjimiphoton]

add about a 2.2k resistor between ground and emitter of q1, and about 4.7k between  the same on q2. that will limit the gain of the transistors into the ballpark of the gain you're looking for. you may need to adjust bias a little via the 8.2k resistor feeding c of q2, so use a 10-20k trimpot to compensate, and you should be able to get a good classic ff tone.

them transistors are perfect for colorsound overdrives, btw

[Electric Warrior]

do i have to worry about the high level of Hfe? i've read online that good q1 q2 for fuzzface have hfe about 70/100 for q1 and 100/140. will it work the same also with the same schematics?

From 1969 onwards the Fuzz Face used BC108C transistors. The high gain actually helps to bias silicon transistors. 70/100 is probably too low for silicons in a circuit without any tweaks.

[pinkjimiphoton]

indeed, electric warrior is right.

but adding small resistances to the e/ground connections can make the gain softer, more responsive, and closer to the sweetness of the early germanium devices.

bias from the c, but set the gain with e.

i'd suggest doing it on the breadboard first, and using a pair of 10k pots between emitter and ground, one for each q. then ya can dial it in to where it sounds best to your ear, <and i bias via c on q2 to get the sweet spot with the smoothest transition from guitar pegged/fuzz to guitar rolled back/clean>
then measure the resistance of the pots, and replace with the next standard resistor sizes ya got. you have an EASY 20% tolerance in there, but i'd bet around 2.2k and 4.7k will be about right. generally ya want about double the resistor value of q1's e to ground resistor, but differences in the transistors themselves can change that some.

adding the resistors will soften the fuzz considerably. its a good way to set the gain range for the transistor, to get it in the ballpark that's most musically linear. then adjustment of the 8.2k resistor, and sometimes the 470/330r resistor too. but usually a small resistance is good, then try a trim at the 8.2k resistor.

a lot of the ff's i build that are silicon i use mpsa06, their gain is pretty consistently around 200. so for those i think i use like, 220r for q1, and around 140r for q2. that seems to set the gain range around where it will work with stock fuzzface passive values.

ymmv and should. experiment. you got dis!

[dschwartz]

But..if you add those emmiter to ground resistors, aren't you introducing degenerative feedback? Thus, hardening the clipping? Or is it not much to be noticeable?

[BluffChill]

Andrea - this is a nice one which uses 2 x BC109s, but I used 108s and it sounded great. Very reactive to your guitar's volume control too, so roll it back and it cleans up to a nice overdrive.



http://tagboardeffects.blogspot.com/2017/05/emanating-fist-electronics-black-dust.html

[bamslam69]

Bluffchill, I recently built the EFE black acid. Pretty cool fuzz! Nice stoner sounds.
I've got some leftover BC109's, and a big dial off an old stereo, so I'll have some fun with the black dust.

[pinkjimiphoton]

But..if you add those emmiter to ground resistors, aren't you introducing degenerative feedback? Thus, hardening the clipping? Or is it not much to be noticeable?

i think if you bypass the resistors with a cap you will get degenerative feedback, but no, the e resistors sweeten the clipping. very noticeable.

fuzzes are weird. they follow their own rules pretty much. almost all rules go out the window. in most applications, people are seeking to limit distortion, weirdos like me seek to invoke it.