Author Topic: Which BC108 for a silicon Fuzz Face?  (Read 10185 times)

nico13

Which BC108 for a silicon Fuzz Face?
« on: December 08, 2008, 08:28:38 AM »
BC108 A, B or C?

In other words, what hfe would you recommend for Q1 and Q2 to get this fuzz sound (guitar solo starts at 1:14):

http://fr.youtube.com/watch?v=6y1bTyOMqqU

I'm about to build a silicon Fuzz Face and any help is welcome.

Thanks.
« Last Edit: December 08, 2008, 08:31:54 AM by nico13 »

newfish

Re: Which BC108 for a silicon Fuzz Face?
« Reply #1 on: December 08, 2008, 08:46:40 AM »
Lower gain device should be Q1 - so use a plain (no suffix) 108 for Q1, followed by a 108A or 108B for Q2.

Incidentally, I built mine using BC107s - no suffix. Hfe is obviously higher than the Ge devices, but still sounds good.

Incidentally, you can vary the gain of Q1 and Q2 by increasing / decreasing the load resistors coming from the +9v.

From memory, I used 33K to feed Q1 and a 8K2 to feed Q2.

I'll dig a diagram out this evening if there's time.
Happiness is a warm etchant bath.

nico13

Re: Which BC108 for a silicon Fuzz Face?
« Reply #2 on: December 08, 2008, 10:45:23 AM »
Thanks Ian,

I dont' know about the hfe of the BC108 (without suffix). Do you I need a BC108 with a hfe of 70-90 as recommended in a germanium Fuzz Face or a higher one for Q1?


I also plan to use the usual collector resistors for Q1 and Q2 (as you used).

I read that some used trimpots (50K and 10K instead of the 33K and 8.2K resistors) to set the voltage on the transistors' collector. Is it really necessary as I will use a 9V regulated power supply? Does the voltage on a transistor's collector depend on the transistor's name / hfe?

newfish

Re: Which BC108 for a silicon Fuzz Face?
« Reply #3 on: December 08, 2008, 11:43:14 AM »
I've built a few NPN Si Fuzz Faces now - and always use two identical trannies for Q1 and Q2 - trusting that the Collector Resistors will sort out the gain - my FF of choice is my most recent build with identical Q1 and Q2 (both BC107s).

Traditionally, Q1 would always have a lower gain than Q2 I think.

I've never needed to use trimpots on Si FFs, as all the components tend to do what they should.  I wouldn't want to build a Ge device without a trimpot - but that's another story.

Your best bet would be to put sockets on your board and audition different trannies for Q1 and Q2.

I could PM you a schematic if that would help - although it sounds like you're up and running...

Happiness is a warm etchant bath.

foxfire

Re: Which BC108 for a silicon Fuzz Face?
« Reply #4 on: December 08, 2008, 12:09:23 PM »
even better than using sockets would be bread boarding it before you build. there are a 1000 and 1 mods/changes you can make in this little circuit. you'll learn twice as much about it to boot. also there are pages and pages of posts on the FF so if you haven't already get yourself a good cup of hot chocolate and settle in...
rylan

nico13

Re: Which BC108 for a silicon Fuzz Face?
« Reply #5 on: December 08, 2008, 02:22:10 PM »
I also could try these:

http://www.banzaieffects.com/Fuzz-Face-Classic-Si-Transistor-Set-pr-13733.html

But as I already have some BC107 i will first try with them and order some BC108 (A,B,C) to test.

bumblebee

Re: Which BC108 for a silicon Fuzz Face?
« Reply #6 on: December 08, 2008, 04:32:00 PM »
Personally, I Use BC109C, they are high gain and sound really nice to my ears.

nico13

Re: Which BC108 for a silicon Fuzz Face?
« Reply #7 on: December 08, 2008, 05:38:39 PM »
Personally, I Use BC109C, they are high gain and sound really nice to my ears.

Bumblebee,

What is the hfe of your BC109C?

slacker

Re: Which BC108 for a silicon Fuzz Face?
« Reply #8 on: December 08, 2008, 05:56:54 PM »
I don't think it matters whether you use BC108s or 109s you just want ones that have a hfe of somewhere around 300-400. That means you either want modern "B" ones or old ones which don't seem to be split into A, B or C types, in my experience they tend to have a hfe of about 350.

I built a fuzzface using a pair around 350 hfe and with a bit of tweaking it gets close to the Dave Gilmour tone, or as close as I'm ever going to get to it  :)

nico13

Re: Which BC108 for a silicon Fuzz Face?
« Reply #9 on: December 08, 2008, 06:04:54 PM »
Thanks for the advice Slacker,

With such high gain transistors does it matter to keep the lower one as Q1.

What do you mean by "with a bit of tweaking"? Using trimpots on the collectors? Changing caps?

slacker

Re: Which BC108 for a silicon Fuzz Face?
« Reply #10 on: December 08, 2008, 06:33:18 PM »
No it doesn't make much difference if Q1 has a lower hfe than Q2.
I think I used a 560R instead of the 330R for a bit more volume and I added a 470p cap from the input to ground to get rid of some radio interference I was getting. I used a 47k volume pot because that's what I had, I think that reduces the bass a bit.

Electron Tornado

Re: Which BC108 for a silicon Fuzz Face?
« Reply #11 on: December 08, 2008, 10:18:05 PM »
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bumblebee

Re: Which BC108 for a silicon Fuzz Face?
« Reply #12 on: December 09, 2008, 04:19:03 PM »
Personally, I Use BC109C, they are high gain and sound really nice to my ears.

Bumblebee,



What is the hfe of your BC109C?
600+

Joe Hart

Re: Which BC108 for a silicon Fuzz Face?
« Reply #13 on: December 09, 2008, 06:03:37 PM »
I built a FF using BC109's and it sounds great! And this was back when I knew NOTHING about the FF circuit. I just built it, adjusted the bias, and I still use it today (maybe 3-4 years after building it). Also, other people have commented on it. They claim it has an "older FF vibe," which I take to mean GE. I like it!!
-Joe Hart

bumblebee

Re: Which BC108 for a silicon Fuzz Face?
« Reply #14 on: December 09, 2008, 06:31:09 PM »
True, I like higher gain fuzz faces, they sound fuller, thicker and just all round nice to me. If I'm making a PNP Ge one I try to get trannies at least 220hFE for Q2 a little lower for Q1 is fine. Banzai have them at this gain level and they sound nice too, actually all banzai AC128's I've got sound pretty good. The only fuzz face derivative I like with lower gain trannies is the woolly mammoth, Q1 needs to be around 150 for the gate to work right, if its over 200 it wont work at all. You can have 150 in Q1 and 600 in Q2 and it sounds pretty cool, I've experimented extensively with the WM and it has a lot that can be done to it to get TOTALLY different sounds out of it. The tonestack isn't the best,but you can always change that but overall its a pretty good fuzz face type pedal.
« Last Edit: December 09, 2008, 06:35:26 PM by bumblebee »

j-pee

Re: Which BC108 for a silicon Fuzz Face?
« Reply #15 on: May 03, 2021, 09:00:51 AM »
Lower gain device should be Q1 - so use a plain (no suffix) 108 for Q1, followed by a 108A or 108B for Q2.


as to "no suffix" / "ungraded" 108... (or 109)
I've just read that they are usually higher in HFE than "C" versions...
but measuring it helps either way

Big Monk

Re: Which BC108 for a silicon Fuzz Face?
« Reply #16 on: Yesterday at 07:07:22 PM »
Lower gain device should be Q1 - so use a plain (no suffix) 108 for Q1, followed by a 108A or 108B for Q2.


as to "no suffix" / "ungraded" 108... (or 109)
I've just read that they are usually higher in HFE than "C" versions...
but measuring it helps either way

You’re a little late... ;)
“We are what we repeatedly do. Excellence, therefore, is not an act, but a habit.” Aristotle

"Beneath the bebop moon, I'm howling like a loon, for you..." Marc Bolan

Fancy Lime

Re: Which BC108 for a silicon Fuzz Face?
« Reply #17 on: Today at 01:08:21 AM »
Hihi, strangely coincidental necrobump. I was about to chime in because I also have a high gain So FF on my breadboard at the moment but then I saw the age of the thread. I need to do some more experimentation before making statements about the influence of transistor gain anyway.

Cheers,
Andy
My dry, sweaty foot had become the source of one of the most disturbing cases of chemical-based crime within my home country.

Rob Strand

Re: Which BC108 for a silicon Fuzz Face?
« Reply #18 on: Today at 03:29:42 AM »
Quote
as to "no suffix" / "ungraded" 108... (or 109)
I've just read that they are usually higher in HFE than "C" versions...
but measuring it helps either way
I don't think that is true and it's not what I've seen throughout my life.

My understanding is the uncategorized version is just chosen at random.  The datasheets show a wide range of possible hFE values.   The idea is they are cheaper.  In practice I didn't see much difference.   An interesting dilemma is how they could guarantee the part is in spec without measuring hFE, it is possible but with some risk attached.

« Last Edit: Today at 03:56:11 AM by Rob Strand »
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