Fuzz Face Mod

[dstrats]

Hi all,

First message here. I found the site looking up stuff about Fuzz Faces (my favorite effect). This seems like a cool place to ask stuff so here I go.

I own a Dunlop Fuzz Face circa '90s that employed bad sounding NKT275s'. I prefer silicone trannies so my tech friend and I went to work.

We reversed the battery leads and the capacitors to make it NPN. I bought two NTE123A that are pretty much like BC109C, as told to me by the sales guy in a component store. As for everything else we left alone besides putting in a .01uf capacitor.

Now, the thing is super saturated which is good, but the tone is very nasal, which I don't like. And it has a "Gated" feel to it. Quick runs on the fretboard sound squashed. Plus, it sounds more like an PE Experience pedal (like it wants to take it an octave higher), rather than an awesome '70s Si Fuzz Face, which is what I was going for. Looking into my prob on the internet I see that the trannies need biasing. My prob is, I don't know how and where to place an internal biasing pot on the board. And, I feel like if the vintage FFs' that I'm trying to capture didn't need a bias pot why do I?

So, is there a way to bias the trannies and get that sweet, full, warm, si fuzz without installing a bias pot?

I look forward to some replies. I hope my question isn't too dumb. Any advice will be much appreciated. Thanks in advance.


-D

[raulgrell]

I'm not familiar with that particular circuit, but make sure you reverse any polarized caps, as running them the wrong way round may cause them to explode.

Negative side to ground!

Also, you probably will have to change the biasing resistors in the circuits (the ones that lead from the power supply to the collector of the transistors. if you don't wanna put in a pot, just solder on some sockets and try different value resistors.

In order to get rid of th nasal sound, you're gonna have to mess around with the caps in/around the signal path. I'm not exactly sure what you have to do objectively, but I think you'd have to swap out the input cap for something slightly bigger...

[snarblinge]

raulgrell, is right the input and output caps will give you more low end at the expense of a little gain.

you don't need to leave a bias pot in there, just put one in till you get it set right then pull it back out and pop in the correct resistor for it to bias up correctly.

the reason the factory didn't need one is the trannies in there all bais about the same so they found a value that worked and stuck with it.

leaving the bias pot in there goes give you the ability to dial in crazy sounds, this is the basis of the Fuzz factory, and one of the standard tweeks people do when building their own Faces.

there is only really one resistor you need to tweek, but we may need a pic of your board to point you in the right direction. I know which one it is on my layout but I have never tweeked a standard one. someone else on here may be able to help out  without a pic tho. welcome to pedal building

[jayp5150]

Get the bias right first, and go from there. The tone of the circuit can change with the bias (usually in the mids).

Any idea what your voltages are currently? (no pun intended lol)

[Quackzed]

it may just be the biasing. if you use a trimmer for the collector resistors, you can dial in a gated/nasaly sound, or dial in an ungated sound just using the pot.
just find the resistors connected to the collectors of the trannies , and replace them with 100k trimmers, that is- lug1 to the collector and lug 2 +3 connected together and wired to the other side of where the collector resistor was connected. then you can adjust the amount of resistance and dial in a sound. if you have a dmm, you can shoot for 4.5v at the collector of each resistor. should be a good starting place.

[Der Groovemeister]

I also recommend lower gain trannies. BC109C's are pretty high gain for a FF.

[mac]

Welcome to the forum.
I do not use high gain silicon like bc109 for this circuit, but there is a trick you can try to reduce Q1 gain: add a 100 - 470 ohm resistor at the emiter.
No need to tweak Q2 since it has the fuzz control.

mac

[raulgrell]

Another trick worth looking into is piggybacking... basically, connecting two transistors in parallel, minus the collectors.

This can also be achieved by placing a diode across the base and emitter, can't remember the orientation, but if you test your trannies hfe you should see a huge fall in hfe when you have it the other way round.

[petemoore]

  Board the FF Testboard:
  Long on IC sockets and resistor legs.
  Use the resistors legs to reduce resistances, start with 150k feedback resistor then decide the lower value you want, clip a pot on the above board resistor legs [left long for just such occasions] or tack a resistor [use the +/- about ~250k ~200kpot to figure out what as for sound sampling/determining the final value[s.
  Dual 8 pin IC sockets for input/output caps and resistors.
  4k7 + 10k pot as Q2 collector resistor, put 4k7>10k trimpot there.
  If you socket or make easy swap conditions for the 22uf, you can easily reverse polarize that..the Q swaps can allow you to find your GE, SI and any other FFace type tones available from the 2 transistor feedback loop gain stage amplifier circuit [fuzzface].

[dstrats]

Hi all!

Thanks for all the great replies. I truly appreciate them.

Someone asked to see a pic of the board so here it is:



A bad pic, I know, but this is what I'm working with. Now, I will warn you all, I'm very new to all this so I may sound stupid. I don't mean to frustrate in advance.

So going by the pic, my friend and I reversed the two big blue cans to make it NPN. It was originally PNP. We also reversed the battery leads. We placed a .01uf cap, that's the white thing in front of the three resistors. Also, installed two NTE123A (US replacement for BC109C). I understand that 109 may be too much but I thought it would sound good. I own a Crest Fuzz Face as well that employs an actual BC109C and a Japanese tranny SK3245 (which is a silicone). I like the tone from the Crest but I need to retire it due to consistency probs. This is why I wanted to mod the Dunlop to a Si FF so I can use it primarily.

I don't know a lot so what I can say is very limited. I don't know how many volts it's running with as one of you asked. I don't know what resistor hits the trannies first so I don't know which controls the tone. That's the main thing I need to know. All the parts, besides the two NTE123As' and the .01uf, where in with the OEM NKT275s'. Nothing else has been changed. I don't know what to change to change the sound or to bias the trannies correctly.

Being that I am such a beginner is there anything on-line or a book y'all can suggest that I can read to learn this side of electronics so I'm not so much in the dark with this project?

Well, again I thank all for the replies. I know I didn't leave y'all with much but I look forward to some replies. Thanks in advance!

-D

[Quackzed]

o.k.
there are a few options here...
option 1.
you could find some silicon trannies that work in the circuit as it is. (swap out the 109's for some lower gain trannies)
     (radio shack sells an assortment  pack of low gain npn transistors(2n2222, 2n3904, and other types)
-best way to try different trannies without re soldering 10 times and maybee messing up the board would be to remove the transistors and solder 3 pin sockets to where the transistors were, and try different npns by plugging them into the sockets.
option 2.
change the 8.2k (grey-red-red-silver) resistor on your board (collector resistor of q2) to something  a little bigger like 15k brown green orange silverorgold which may or may not give you a better tone(dependant on the transistors needs).most transistors will bias up well with a resistor from between 8k and 30k but its hard to say weather 15k will be right for yours.

i'd say go with #1, which leaves you the option of trying different trannies and hearing the differences between them. should make it easier to get what you like without too much fuss, and is easier to try different tones easily, or go back and forth between different ones later on...

[Electric Warrior]

I also recommend lower gain trannies. BC109C's are pretty high gain for a FF.

should be in the same gain range as the BC108Cs they used in the early 70's.

[zombiwoof]

If you compare the circuit of the silicon fuzz faces against the germanium version, you will see that they also changed at least one resistor value in the silicon FF, you might want to do that also.  And you are going to have to either pick transistor values that will work with the stock circuit, or change the bias resistors to get the trannies biased correctlly.  I would suggest replacing at least one bias resistor with a trimpot to dial it in.

Al

[Talon5051]

is there anything on-line or a book y'all can suggest that I can read to learn this side of electronics so I'm not so much in the dark with this project?

Here is a good source of information on the fuzz face http://www.geofex.com/Article_Folders/fuzzface/fffram.htm.  Geofex has a lot of good information on a wide variety of electronics.  I think it is safe to say that most of the people in this forum have benefited from this site and R. G. Keen.

[zombiwoof]

raulgrell, is right the input and output caps will give you more low end at the expense of a little gain.

you don't need to leave a bias pot in there, just put one in till you get it set right then pull it back out and pop in the correct resistor for it to bias up correctly.

the reason the factory didn't need one is the trannies in there all bais about the same so they found a value that worked and stuck with it.

leaving the bias pot in there goes give you the ability to dial in crazy sounds, this is the basis of the Fuzz factory, and one of the standard tweeks people do when building their own Faces.

there is only really one resistor you need to tweek, but we may need a pic of your board to point you in the right direction. I know which one it is on my layout but I have never tweeked a standard one. someone else on here may be able to help out  without a pic tho. welcome to pedal building

Actually, the original Fuzz Faces could have benefited from the use of a bias pot.  Many of those Fuzz Faces sounded like crap, because the transistors varied in gains, and they didn't do anything to correct for the differing gains.  There are famous stories of guys like Jimi Hendrix and Eric Johnson going through piles of Fuzz Faces in order to find one or two that sounded right.  Getting the bias right is the key to a good sounding FF, as many people here know.

Al

[dstrats]

Actually, the original Fuzz Faces could have benefited from the use of a bias pot.  Many of those Fuzz Faces sounded like crap, because the transistors varied in gains, and they didn't do anything to correct for the differing gains.  There are famous stories of guys like Jimi Hendrix and Eric Johnson going through piles of Fuzz Faces in order to find one or two that sounded right.  Getting the bias right is the key to a good sounding FF, as many people here know.
Al

Hi all,

Thanks again for all the replies. And thanks for the link for the info about Fuzz Faces.

Going by this reply I quoted I guess a trim pot would be the best way to go, and also those devices that allow you to put whatever tranny you want without having to solder each time.

So, my new questions are, where would I place the trim pot on the FF board I'm working on? Do y'all know which model of trim pot I'd buy and how I'd solder it up? And, where can I find those 3 pin sockets?

Thanks again for all the replies on my topic. It's great to be on a forum with such helpful folk. Take care! 

-D

[Quackzed]

you can find both parts right here in the store...
sockets... (store) 4 single row sockets 2.00, (Store)(parts)100k trim pot .55.
1. you would cut the transistors off, and solder a socket for each leg of the transistors.
2. you would cut off the grey red red silver resistor(leaving enough legs on it to solder the trimpot to ,and solder in the trim pot like so...
x=removed resistors leads on the board...
0= trimmer lugs

x                 x
  \_0   0__0_/

so the middle lug and one outer lug of the trimpot are wired together and go to one of the cut resistor leads, and the other lone lug goes to the other resistor lead.
-so you can see that, because the middle lug on the trimmer is connected to one of its outside lugs, when you turn it, it's basically making the resistance beween the lone lug and the middle/outer connected lugs  go from 0 to 100k from one extreme to the other. when a pot is wired like this to replace a resistor it's called a 'variable resistor' because it acts like a resistor you can 'vary' the value of.
i do love a nicely tuned fuzz
cheers!

[MmmPedals]

Read technology of the fuzz face here  http://geofex.com/fxtech.htm

[zombiwoof]

you can find both parts right here in the store...
sockets... (store) 4 single row sockets 2.00, (Store)(parts)100k trim pot .55.
1. you would cut the transistors off, and solder a socket for each leg of the transistors.
2. you would cut off the grey red red silver resistor(leaving enough legs on it to solder the trimpot to ,and solder in the trim pot like so...
x=removed resistors leads on the board...
0= trimmer lugs

x                 x
  \_0   0__0_/

so the middle lug and one outer lug of the trimpot are wired together and go to one of the cut resistor leads, and the other lone lug goes to the other resistor lead.
-so you can see that, because the middle lug on the trimmer is connected to one of its outside lugs, when you turn it, it's basically making the resistance beween the lone lug and the middle/outer connected lugs  go from 0 to 100k from one extreme to the other. when a pot is wired like this to replace a resistor it's called a 'variable resistor' because it acts like a resistor you can 'vary' the value of.
i do love a nicely tuned fuzz
cheers!

I don't want to confuse the OP more here, and I know you're trying to promote Aron's store (which is a good idea), but I think a 100k trimpot to replace the 8.2k resistor is a bit overkill.  Plus, I was advised here to always put a small resistor in series with the trimpot in a case like this.  petemoore suggested a 10k trimmer with a 4.7k resistor in series, and this should be adequate.  This would give you 4.7k at minimum and 14.7k at maximum.  I used similar values in my germanium FF, except I think I used a slightly larger resistor.  I soldered the resistor across the middle and one outside lug of the trimpot, then soldered the remaining lug of the trimpot to one of the resistor pads and the free end of the attached resistor to the other pad.  It has worked fine for my FF.  The mid position of the pot gives you a value that is close to the stock 8.2k, and you have room to adjust for less or more resistance to bias the transistor.  If you want to go all the way, you can also use a trimpot to replace the other bias resistor (33k), in that case you would use a 50k trimpot and a small resistor, with both bias resistors you have a lot of room to dial in the bias for a variety of sounds.  Just replacing one of the bias resistors will probably work fine, though.

I would agree with socketing the transistors.  I would also suggest replacing the 470 ohm resistor on the board (which originally was the germanium circuit) with a 330 ohm resistor, as this was the value used in Fuzz Faces when they changed to silicon trannies.  See this page on FuzzCentral on the Arbiter FF's for more info:

http://fuzzcentral.ssguitar.com/fuzzface.php

The GEO Fuzz Face pages that were previously recommended are also required reading IMO.

Al

[dstrats]

Wow guys!

Thanks so much for such a detailed reply with awesome instructions. Man that's great! Thanks "zombiwoof" & "Quackzed". Much appreciation!

OK, so this is starting to make sense. Here's a better pic of the board I'm working on:



So, put the trim pot where the 1st resistor (8.2K) from the top, out of the three resistors, directly under the green cap. Then if I want I to work both trannies individually I place a second trim pot where the 3rd resistor (33K) is? Then change, would it be, the middle out of the three resistors to 330ohm? That sounds easy enough.

Should I do/change anything else like the green cap (2A104K is what is printed on the cap) to something better? Or that lone resistor all the way left on the board to something else? Would it be good to get carbon comp resistors, or is that more for period correct type stuff (i.e... doesn't really matter).

Thanks again guys. Y'all totally rock!! I'm going to order some 10K trim pots. I've read somewhere else that's what all the boutique builders use. So, I DO need to solder a resistor of the trim pot leads, right? Thanks!!!