Help me make a fuzzface

[Se7en_Costanza]

Hey guys,
I need some advice, every time ive tried to make a fuzzface it comes out sounding awful, like broken pedal awful. Ive followed both the basic NPN & PNP schematics for the fuzzface using different transistors (bc108/ac128/2N5088) and it sounds terrible. To describe the sound, i dont get any signal coming though when the fuzz knob isnt at 100%, and when its at 100, the attack of the strum or note i play on the guitar comes through, and the decay is buzzes away, and it all sounds very stuttery.
What am i doing wrong? I've attempted both of these circuits about 3 or 4 times, using both schematics and veroboard layouts.

I've made several more advanced pedals before so i know how things work on a basic/intermediate level, but for some reason the fuzzface never has worked for me, and its killing me.
Please help.

Thanks.

[Se7en_Costanza]

These were two of the schematics i followed.

pnp fuzzface
http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacepnpschematic.gif

npn fuzzface
http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacenpnschematic.gif

[Govmnt_Lacky]

I would highly recommend reading the linked article by RG Keen. It will inform you about the Fuzz Face and give you an understanding of why you might be hearing what you are hearing....

http://www.geofex.com/Article_Folders/fuzzface/fffram.htm

[a2music]

You didn't say anything about biasing the transistors. There is a 99% probability that your problem has to do with biasing.The fuzz face schematics you're looking at give you the stock resistor values. The 33K and 8.2 K resistors in the circuit are responsible for setting the voltage to the collectors of the two transistors but those values rarely work. You can either use trim pots or swap resistors until the voltage is right. The goal is to have the collector of Q1 around -.5v and the collector of Q2 at -4.5v. Depending on the transistors you're using it might take 47K to bias Q1 correctly. It's always a good idea to use a trim pot on Q2 (the more critical of the two voltages) because The voltage will change once the pedal has been sitting overnight after the transistors have been handled. I can post an updated schematic or strip board layout if you like.


Sent from my iPhone using Tapatalk

[smallbearelec]

You didn't say anything about biasing the transistors.

Agreed.

Please check out this article on breadboarding the FF:

http://diy.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

The 2N5088 is definitely higher gain than the circuit likes, and the BC108 can be, depending on the make. Set it up on the breadboard first and get the bias lined up. When you have it sounding good on the breadboard, you can commit to solder with confidence.

[Gus]

There have been many threads about FF circuits at this forum.
Search for
"one knob fuzz"
"meathead"
"tonebender"
"supa fuzz"
"fuzz face biasing"
"fuzz face design"
etc.

Also don't get stuck with the Q2 collectors has to be 1/2 9VDC(4.5VDC) and the first at some other voltage. One of my favourite silicon one knob FF builds has Q1 1.6VDC and Q2 7VDC
I have posted a one knob FF like circuit with 2N5089s that might help you with biasing
Most of the resistors affect the biasing not just the ones in the Q2 collector

Running a sim of the circuit often helps with setting up a FF

[karis12]

Some place on the Internet called Analog Alchemy helped me find the correct resistor values for my build (BC548 transistors, negative ground). You just need a way to measure the gain of the transistors you will be using.

[Electric Warrior]

You didn't say anything about biasing the transistors. There is a 99% probability that your problem has to do with biasing.The fuzz face schematics you're looking at give you the stock resistor values. The 33K and 8.2 K resistors in the circuit are responsible for setting the voltage to the collectors of the two transistors but those values rarely work. You can either use trim pots or swap resistors until the voltage is right. The goal is to have the collector of Q1 around -.5v and the collector of Q2 at -4.5v. Depending on the transistors you're using it might take 47K to bias Q1 correctly. It's always a good idea to use a trim pot on Q2 (the more critical of the two voltages) because The voltage will change once the pedal has been sitting overnight after the transistors have been handled. I can post an updated schematic or strip board layout if you like.


Sent from my iPhone using Tapatalk

I wouldn't say the stock values rarely work. As long as the transistors are reasonably matched they work really well for a wide range of types and within a wide range of measured voltages.

Hey guys,
I need some advice, every time ive tried to make a fuzzface it comes out sounding awful, like broken pedal awful. Ive followed both the basic NPN & PNP schematics for the fuzzface using different transistors (bc108/ac128/2N5088) and it sounds terrible. To describe the sound, i dont get any signal coming though when the fuzz knob isnt at 100%, and when its at 100, the attack of the strum or note i play on the guitar comes through, and the decay is buzzes away, and it all sounds very stuttery.
What am i doing wrong? I've attempted both of these circuits about 3 or 4 times, using both schematics and veroboard layouts.

I've made several more advanced pedals before so i know how things work on a basic/intermediate level, but for some reason the fuzzface never has worked for me, and its killing me.
Please help.

Thanks.

Could you post voltage measurements between all transistor leads a ground, please? If there's something wrong with your build it will probably result in some unusual readings.

A link to the veroboard layout you used would also be useful.

Once it all turns out to be alright it's time to measure and audition transistors...

[Rob Strand]

The 33K and 8.2 K resistors in the circuit are responsible for setting the voltage to the collectors of the two transistors but those values rarely work.

For silicon transistors I'd say the same.  Resistor on the collector Rc = 5.6k would be a good starting point - say 4.7k to 6.8k in general.

Frank has a nice calculator.  I threw in a few numbers and it looks pretty close,
http://www.muzique.com/lab/fuzz_face.php

[Electric Warrior]

I've used this quite often and I don't see any problems with the stock values. The voltages are sometimes a bit off from what I'd expect (and measure) in real life, but the overall mechanics work rather well.


https://picload.org/image/raiwpclw/screenshot.jpg
https://picload.org/image/raiwwlol/lowgainsilicon.jpg
https://picload.org/image/raiwwloa/germanium.jpg

[dennism]

Lots of good replies above, but here's what worked for me when I was having the same problems as the OP.  Start with the silicon pedal, easier to work with than germaniums when you're starting out.   Use a really low gain silicon NPN like the 2N4123 for both of the transistors.   Put a small value capacitor, 100-150pf across the C and B leg of each transistor.    Result for me has been a great smooth, usable fuzz face pedal.

[Rob Strand]

The voltages are sometimes a bit off from what I'd expect (and measure) in real life

For the silicon, Vbe of 0.55V seems a bit low, and it helps those results get closer to 4.5V.  A vbe of 0.60 to 0.65V is more like it and that usually results in a low Q2 collector voltage.  (One of my marked-up schematics shows Vbe=0.63V)

For germanium, it sometimes works out ok, depending on leakage.

[Rob Strand]

Put a small value capacitor, 100-150pf across the C and B leg of each transistor.    Result for me has been a great smooth, usable fuzz face pedal

I like it on Q2.

I had these AC128 looking transistors which sounded good in the Q2 position.  I thought they were NPN germaniums  but when I measured them I realized they were silicons.  They had a lot of capacitance.

[LightSoundGeometry]

I've used this quite often and I don't see any problems with the stock values. The voltages are sometimes a bit off from what I'd expect (and measure) in real life, but the overall mechanics work rather well.


https://picload.org/image/raiwpclw/screenshot.jpg
https://picload.org/image/raiwwlol/lowgainsilicon.jpg
https://picload.org/image/raiwwloa/germanium.jpg

i read an article on gearpage from like 2000 on the fake trannies that went around back then and a lot of the thread spoke to the fact so many abnormal bias values were spotted in builds to help solve the mystery of the fake trannies. ..basically they were looking for normal bias resistors in a certain ballpark

EW ..can you tell me anything about this false leakage resistor to base of tranny that is not in a real schematic? these are a pain to get right lol ..I guess you just want a little leakage to turn on the transistor at the base of Q1 ?

[Electric Warrior]

The voltages are sometimes a bit off from what I'd expect (and measure) in real life

For the silicon, Vbe of 0.55V seems a bit low, and it helps those results get closer to 4.5V.  A vbe of 0.60 to 0.65V is more like it and that usually results in a low Q2 collector voltage.  (One of my marked-up schematics shows Vbe=0.63V)

For germanium, it sometimes works out ok, depending on leakage.

I used the value from the Telefunken BC108C datasheet. Not sure if I picked the right one, though?



From what I understand, Q1B voltage in a Fuzz Face equals Vbe.
0.6V may be a tad closer to the truth, but 0.55V is definitely closer than 0.65V, judging by the readings I've got.
Most of the high gain silicon units seem measure over 5V on Q2's collector, so my guess is the math is off a little.
Interestingly, germaniums seem to have a lot lower Vbe than what is usually suggested.

It sure is possible to bias a germanium Fuzz Face to -4.5V with the stock values (yup, low leakage is key) and a couple of vintage units are, but most have a much higher collector voltage than that. The numbers I put in (and got out) should be fairly realistic. They may not be precise, but roughly in the right ballpark.

I've used this quite often and I don't see any problems with the stock values. The voltages are sometimes a bit off from what I'd expect (and measure) in real life, but the overall mechanics work rather well.


https://picload.org/image/raiwpclw/screenshot.jpg
https://picload.org/image/raiwwlol/lowgainsilicon.jpg
https://picload.org/image/raiwwloa/germanium.jpg

i read an article on gearpage from like 2000 on the fake trannies that went around back then and a lot of the thread spoke to the fact so many abnormal bias values were spotted in builds to help solve the mystery of the fake trannies. ..basically they were looking for normal bias resistors in a certain ballpark

EW ..can you tell me anything about this false leakage resistor to base of tranny that is not in a real schematic? these are a pain to get right lol ..I guess you just want a little leakage to turn on the transistor at the base of Q1 ?

As long as every other builder thinks a Fuzz Face must measure 4.5V on Q2's collector, looking for certain bias resistors is a waste of time if you're trying to identify fake or reproduction transistors.

Why bother simulating leakage in only one transistor? Use really low gain silicons and add leakage to both until it biases to your liking.. You could use a trim pot and a limiting resistor between the collector and base, like in a Soul Bender. Let us know how it goes!

[Rob Strand]

I used the value from the Telefunken BC108C datasheet. Not sure if I picked the right one, though?
0.6V may be a tad closer to the truth, but 0.55V is definitely closer than 0.65V

You are right those BC108C's are a bit lower than what I gave and a bit higher than yours.
So yes, 0.6V is a bit closer to the truth.

In the FF Q1 operates at about Ic=0.24mA and Q2 at about Ic=0.6mA. In the Telefunken data the 2mA value is closer than the 0.1mA value. Vbe varies with current.  The table below estimates Vbe at the actual currents for Q1 and Q2.  The are based on the two Telefunken specs  and the Philips BC54x specs.  The Philips BC10x specs is the same as the Telefunken 2mA spec.  (You can do this using Vbe_new = Vbe_spec + 0.026 * ln (IC_new/IC_spec))
         
Specs:   
                        TF BC108            PH BC548
                   Spec 1      Spec 2    typ.
Ispec [mA]    0.1         2.0       0.5
Vspec [V]        0.55        0.62       0.6
         
Q1
Icalc [mA]  0.24        0.24          0.24
Vcalc [V]     0.57        0.56          0.58
         
Q2
Icalc [mA]    0.6   0.6         0.6
Vcalc [V]      0.60   0.59         0.60

So for Q1 it is between around 0.57V and for Q2 around 0.60V.

Most of the high gain silicon units seem measure over 5V on Q2's collector, so my guess is the math is off a little.

In circuits, I can't say I've ever got voltages over 4.5V with the standard parts.   Not sure what is going on here.

Chucking the correct Vbe's in the calculator I get:
hfe     Vc2
200     2.94V
400     3.43V
800     3.68V

Those are in the ball-park of what I remember.
Maybe I need to dig-up some BC108s and check again.

[Electric Warrior]

I just hope it's not some magic mojo thing only vintage Telefunken transistors will do. 

[Rob Strand]

I just hope it's not some magic mojo thing only vintage Telefunken transistors will do. 

That's got to be it!

[Se7en_Costanza]

Firstly thanks for the replies here guys this is all super helpful and sorry for a late reply.
I wasn't as familiar with biasing and the theory side of pedal building and electronics so all of this is new to me.

I'll breadboard, both the npn/pnp fuzz faces again, and try and get Q1 at 0.5v and Q2 at 4.5v. If I'm still having problems ill report back. Also, If i was to add a bias knob on the exterior of a fuzz face controlling Q2's collector resistance would that help this issue? and if its a good idea what value pot would you recommend?

Also speaking of biasing, can someone explain to me or point me to a thread about what biasing transistors actually means in the terms of pedal building/electronics theory and the sound differences between them. Is this a crucial part of any fuzz to bias the transistors? like what are the difference in biasing between say a fuzz face to a big muff? or the DbA fuzz war?

Also i should mention that the ac128 pnp transistors i have im not sure if they are fake or not, im not the best with telling, but i did get them from eBay for $2 for both of them, so there is a huge possibility they are fake, but even so i thought they'd still show some signs of pleaseable gain being a germanium transistor. I'm waiting on a transistor tester to arrive so i can measure them though.

[Gus]

some links for Si FF like circuits, left of input is a simple guitar cable sim do not built that part
first shows a 2n5089 circuit
http://www.diystompboxes.com/smfforum/index.php?topic=114153.msg1058953#msg1058953
http://www.diystompboxes.com/smfforum/index.php?topic=114210.msg1059856#msg1059856


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