Need help troubleshooting fuzz face

[Rick899]

I have been trying to build a fuzz face pedal. I have found several schematics and layouts. 

I built the FF5 fuzz face from General Guitar Gadgets on a perfboard and could not get the fuzz effect to work even after  making several fixes. With the 2n3906 I  got clean guitar on bypass and the battery got very hot.

I built another FF  on a breadboard from a schematic titled  "Fuzz Face Dallas Arbiter" I found on www.pisotones.com.  This one called for a .1 uf cap instead of the .01 uf cap that all the other schematics  had. That one partially worked  in that the volume pot regulated volume but the fuzz pot had no effect.

I found a layout titled "1966 Germanium Fuzz Face" on www.turretboard.com.  I built that one on a breadboard and it sounded good with full fuzz effect. I put it onto a RS perfboard and it didn't work right. On the perfboard with the 2n3906 I got normal guitar on bypass and diminished volume with no effect with the effect switched on.  I have double, triple and quadruple checked and compared the two to find the problem, but I am stumped.

The transistors:   I  tried the pedals with four  AC 128  Germanium transistors  and  some 2n 3906  transistors.  The test results for those transistors are as follows:

2n3906:  -B+C:   .722     (The negative and positive signs refer to the DMM test leads)
      -B+E:   .725
      +E-C:  1.
      -E+C:  1.

AC128:   1.  -B+E:  .185
            -B+C:  .144
            +E-C:  1.278  (and continues to increase if you leave the leads connected)
            -E+C:  .086

   2.  -B+E:  .185
        -B+C:  .183
        -C+E: 0
        -E+C:  0

   3.  -B+E:  .186
        -B+C:  .177
        +E-C:   1.
        -E+C:  1.

   4. -B+C:  .167
       -B+E:  .168
       -E+C:  1.
       +E-C:  1.

My questions: 
1.  Based on the readings above are  AC 128 one and two above bad? 
2.  Are the .186/.177 and .167/.168 readings for AC 128 three and four, too low (I read that these readings should be between .4 and .7; although the 1966 FF sounded good on the breadboard with these two transistors)?      What is going on?
3. Can you tell anything else about the transistors from the test results above?
4. Why did the battery get hot when the guitar was coming through normally on bypass on the GGG FF5? 
5. Can anyone who has built fuzz face pedals shed any light on what could be the problem?
6. Are these PNP germanium fuzz face pedals always going to be problematic and limited by the quality of the transistors one can find for them?
7.  Can something in the circuit damage these germanium transistors?
8. The note to the 1966 FF says  "Bias 8k2 resistor to have close to 5v on Q2C".  How is this done?           
9. Could failure to bias the 8k2 resistor contribute to these problems?      (Although logically it would seem that it wouldn't because it works on the breadboard) 

I apologize for the long post. Thanks for any help you all can provide.

[Rick899]

Another fact that might be relevant:    The FF that works on the breadboard does not have the switch.  On the perfboard version I used the switch and jack connections found on this site under the beginner's boost project.  For the GGG FF5 I used the switch and jack connections on their layout and wiring diagram.

[LucifersTrip]

I have been trying to build a fuzz face pedal. I have found several schematics and layouts.  

I built the FF5 fuzz face from General Guitar Gadgets on a perfboard and could not get the fuzz effect to work even after  making several fixes. With the 2n3906 I  got clean guitar on bypass and the battery got very hot.

I built another FF  on a breadboard from a schematic titled  "Fuzz Face Dallas Arbiter" I found on www.pisotones.com.  This one called for a .1 uf cap instead of the .01 uf cap that all the other schematics  had. That one partially worked  in that the volume pot regulated volume but the fuzz pot had no effect.

I found a layout titled "1966 Germanium Fuzz Face" on www.turretboard.com.  I built that one on a breadboard and it sounded good with full fuzz effect. I put it onto a RS perfboard and it didn't work right. On the perfboard with the 2n3906 I got normal guitar on bypass and diminished volume with no effect with the effect switched on.  I have double, triple and quadruple checked and compared the two to find the problem, but I am stumped.

welcome

First suggestion is to use a confirmed schematic...these have been used a million times here. As you can see, the only difference between SI and GE is the 330/470:
http://fuzzcentral.ssguitar.com/fuzzface.php

secondly, forget about the AC128's now unless you bought a matched pair. As a beginner, go for the silicon first, 2N3906.
remember, both the 128's & 3906's are pnp, so you will be using this (470 w/ AC128, 330 w/ 2N3906):

The transistors:   I  tried the pedals with four  AC 128  Germanium transistors  and  some 2n 3906  transistors.  The test results for those transistors are as follows:
[edited]

I'm not 100% what results you are giving....Are those for Q2?

Regardless, forget about that for now and get your breadboarded version working well. Then, measure the voltages. You should get Q2's collector near -4.5v.  If you don't have the circuit set up correctly on the breadboard, why solder to a board yet...

My questions:  
1.  Based on the readings above are  AC 128 one and two above bad?  

not enough info...you could have easily made a wiring mistake as a beginner

2.  Are the .186/.177 and .167/.168 readings for AC 128 three and four, too low (I read that these readings should be between .4 and .7; although the 1966 FF sounded good on the breadboard with these two transistors)?      What is going on?

yes, the collector should be -4.5v (remember, "-" because it's pnp...black on ground, red on collector)

3. Can you tell anything else about the transistors from the test results above?

miswiring or transistors wrong gains/leakages for the circuit

4. Why did the battery get hot when the guitar was coming through normally on bypass on the GGG FF5?  

most likely a short

6. Are these PNP germanium fuzz face pedals always going to be problematic and limited by the quality of the transistors one can find for them?

more difficult than SI, but easier after you've done a bunch

7.  Can something in the circuit damage these germanium transistors?

a miswired short...you will feel them get hot...also, if you left the soldering iron on one too long, you could damage it

8. The note to the 1966 FF says  "Bias 8k2 resistor to have close to 5v on Q2C".  How is this done?      

substituting a 10-20K pot for the 8.2K and adjusting it

9. Could failure to bias the 8k2 resistor contribute to these problems?      (Although logically it would seem that it wouldn't because it works on the breadboard)  

yes, but .186 is too far off....it's most likely a miswiring or wrong transistors

I apologize for the long post. Thanks for any help you all can provide.

Another fact that might be relevant:    The FF that works on the breadboard does not have the switch.  On the perfboard version I used the switch and jack connections found on this site under the beginner's boost project.  For the GGG FF5 I used the switch and jack connections on their layout and wiring diagram.

no prob...here's what I' do:

on the breadboarded, working version (use the 3906's) sub a 20K pot for the 8.2K and with your black dmm lead on ground and red on Q2C, adjust the pot. If you wired it properly, you should be able to hit -4.5v and get a good fuzz with those 2N3906's.

Make the higher gain of the 2 transistors Q2. report those voltages as Q1 ebc, Q2 ebc

on the perfboarded version, bypass the switch to see if that wiring was the prob.

good luck

[Rick899]

Luciferstrip:

Thanks for the detailed reply.   I n regard to why I did a perfboard version before breadboarding it:   I got too confidant because the first pedal I did, an easier GGG pedal, I got right the first time. So I thought I'd save time and go right to the perfboard. MISTAKE!!!

In regard to the meter readings  of the  transistors, those were done with the transistors out of the circuit. (No heat was ever applied to the transistors. I used sockets.  )   

The DMM  readings of the transistors (AC 128 1,2,3, and 4 are of the four AC 128s that I have (they are not matched pairs)), i.e.,  the .186, etc. were obtained using the following procedure I found online:

Connect the red (positive) lead to the base of the transistor. Connect the black (negative)
lead to the emitter. A good NPN transistor will read a junction drop voltage of 0.4V to
0.9V. A good PNP transistor will read open.
● Leave the red meter lead on the base and move the black meter lead to the collector - the
reading should be almost the same as the previous test, open for PNP and a slightly lower
voltage drop for NPN transistors.
● Reverse the meter leads and repeat the test. This time, connect the black meter lead to the
base of the transistor and the red lead to the emitter. A good PNP transistor will read a
junction drop voltage of 0.4V to 0.9V. A good NPN transistor will read open.
● Leave the black meter lead on the base and move the red lead to the collector - the reading
should be almost the same as the previous test, open for NPN and a slightly lower voltage
drop for PNP transistors.
● Place one meter lead on the collector, the other on the emitter, then reverse. Both tests
should read open for both NPN and PNP transistors.

According to the last test, collector to emitter then reversed, Nos. 1 and 2 don't have open readings. My conclusion: both are bad.

When adjusting bias with the 10-20k pot what do you do with the third lug of the pot?
Anyway, back to the drawing board, as they say.  I am going to start over using the breadboard.

[Rick899]

Continued ....

I figured out what to do with the third lug of the pot:  Terminals 3 and 2 of the pot went to where one lead of the 8.2k  went and terminal 1 of the pot went to where the other lead of the 8.2k went (Q2C).   (Is that right?)     I also put a pot between ground and Q2C and adjusted the bias voltage to -4.5.   You were right.  I got a pretty good fuzz with the 3906s.  The only problem was that  a static like rumbling sound interferes with the signal while sustaining a note and cuts it off.  Any idea what is causing that?     

I substituted the 470R   for the 330R.  The version I am working with is the same as the schematic you posted except for a 22uf  instead of the 20uf.  Now I just have to figure out what mistake I made when I put it on a perfboard.

[LucifersTrip]

Luciferstrip:

Thanks for the detailed reply.   I n regard to why I did a perfboard version before breadboarding it:   I got too confidant because the first pedal I did, an easier GGG pedal, I got right the first time. So I thought I'd save time and go right to the perfboard. MISTAKE!!!

no problem at all...after many, many projects I still breadboard almost everything first. Even if it sounds great, you know with some tweaking you can make it even better..

...were obtained using the following procedure

don't worry about those tests. what you want are the voltages when the transistors are in the circuit and the effect is on.
(black lead to ground, red lead to the lug you are testing)
here's the debug thread you will be invariably pointed to:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

for transistors (especially ge's), before putting them in the circuit, it is very helpful to know the gain & leakage (silicon will be insignificantly low, so don't worry):
http://www.geofex.com/Article_Folders/ffselect.htm

here's the classic article:
http://www.geofex.com/Article_Folders/fuzzface/fffram.htm

I figured out what to do with the third lug of the pot:  Terminals 3 and 2 of the pot went to where one lead of the 8.2k  went and terminal 1 of the pot went to where the other lead of the 8.2k went (Q2C).   (Is that right?) 

the pot is just a variable resistor. all you need to do is connect the middle and either side. if you turn towards the open lug (looking down), the resistance will go to 0.  if you connect as you did that will work also.

   I also put a pot between ground and Q2C and adjusted the bias voltage to -4.5. 

you really shouldn't do that...you'd be changing the circuit. the 20K replacing the 8.2k is sufficient. if you can't get 4.5v on Q2C with that alone, you need to choose different transistors. you should be shooting for close to 8.2K with the pot (hopefully ~ 4K-13k)

You were right.  I got a pretty good fuzz with the 3906s.  The only problem was that  a static like rumbling sound interferes with the signal while sustaining a note and cuts it off.  Any idea what is causing that?     

if you biased it properly at 4.5v, the sustain & decay should be cool. (or you messed up the circuit with the pot from C to ground). though, you may get some static/noise/oscillation with silicons. try a 100-200pf (picofarad) cap across Q1 or Q2 B-C to tame it

I substituted the 470R   for the 330R.  The version I am working with is the same as the schematic you posted except for a 22uf  instead of the 20uf.  Now I just have to figure out what mistake I made when I put it on a perfboard.

stick with the 330. the 470 will only give you more volume and make it more of a distortion & less fuzz. 22uF or 20uF will make no difference

someone may spot the error if you post a closeup pic of the perf...but I'd get the breadboard version to your liking first..

good luck

[petemoore]

  New 2n3906 pretty much qualify as good pnp transistors, the Ge's are a maybe so far, read and build the transistor gain/Hfe measuring circuit at GEO Technology of the Fuzzface article to determine 'goodness' of Ge's for effect usage.
   Starting with SI is recommended, finish is your choice, but making the circuit work requires many things, 1 being usable transistors, 3906 makes the transistor selection process done' as far as working, many a FF stick with the Si transistors, if you 'beat' 'em with Ge's that's another matter, for now just focus on making the circuit working.

[Rick899]

Quote
   I also put a pot between ground and Q2C and adjusted the bias voltage to -4.5.

you really shouldn't do that...you'd be changing the circuit. the 20K replacing the 8.2k is sufficient. if you can't get 4.5v on Q2C with that alone, you need to choose different transistors. you should be shooting for close to 8.2K with the pot (hopefully ~ 4K-13k)

I made a mistake when I wrote the above quote.  I basically did as you said. I replaced the 8.2k with a pot.  I put the  meter between ground and Q2C to adjust  the bias voltage.  And it did adjust to -4.5 v.

    Quote
You were right.  I got a pretty good fuzz with the 3906s.  The only problem was that  a static like rumbling sound interferes with the signal while sustaining a note and cuts it off.  Any idea what is causing that?     

if you biased it properly at 4.5v, the sustain & decay should be cool. (or you messed up the circuit with the pot from C to ground). though, you may get some static/noise/oscillation with silicons. try a 100-200pf (picofarad) cap across Q1 or Q2 B-C to tame it

Since there was no pot from C to ground it must be static/noise/oscillation. I thought I heard oscillation which sounds like a wavering of the signal. This oscillation was minimal but the interruption of the sustain is problematic. I'll try the 100-200 pf cap across  Q1 or Q2 B-C. 

Thanks for the help.

[Rick899]

I built the transistor testing circuit on a breadboard.

I used a fresh battery which measured 9.25 volts. The black DMM lead went to the 2.4k (2.38K actual DMM reading) resistor and the red lead to the "C" lead of the transistor.  I tested each twice. The results are below. the readings before the slash is without pressing switch. The readings after the slash are with the switch pressed.

1. 1.32/2.14    and  2.20/2.90

2. 9.19/9.18    and   9.20/9.20

3. 1.30/2.05   and  2.31/2.81

4.  .48/.83      and   .41/.79

Please help with the interpretation of these results.

[LucifersTrip]

I built the transistor testing circuit on a breadboard.

I used a fresh battery which measured 9.25 volts. The black DMM lead went to the 2.4k (2.38K actual DMM reading) resistor and the red lead to the "C" lead of the transistor.  I tested each twice. The results are below. the readings before the slash is without pressing switch. The readings after the slash are with the switch pressed.

1. 1.32/2.14    and  2.20/2.90

2. 9.19/9.18    and   9.20/9.20

3. 1.30/2.05   and  2.31/2.81

4.  .48/.83      and   .41/.79

Please help with the interpretation of these results.

Here's the key example in the article:
http://www.geofex.com/Article_Folders/ffselect.htm

"Let's say the device really leaks 93uA, and has a gain of 110 - a prime specimen. What happens when we test? We chuck the thing in the socket, and read (93uA)*(2472) = .229V. Then we press the switch, and read 1.330V. To get the real gain, we subtract 0.229V from 1.330V and get 1.101V. The true gain is just 100 times the reading"

Very simply, from that example, you know that .229v is ~ 93uA of leakage. For a FF, you're shooting for really not much more than 200uA or 300uA max, which means ~ .5 - .75v before you push the button. In addition, you want the gain to be ~60-90 for Q1 and 90-130 for Q2

If you set the test up properly, the first 3 leak far too much and the 4th has borderline high leakage with too low gain.
#4 would have a gain of  .83-.48 = .35 x 100 = 35 gain with leakage ~ 200uA   /  .79-.41 = .38 x 100 = 38 gain with leakage ~ 170uA*

*this test is prob more accurate. it looks like you waited longer for the reading to settle

Neither of the 4 are good for a FF.  #1 & #3 could possibly be used in an FZ-1A or variant in the Q3 slot.

[Rick899]

Luciferstrip:

Thanks for interpreting those results.  I understand how you got the gain.   Now let's see if I understand how you got leakage:

If a .229  (almost .23,  the reading before pressing the switch )  reading  equals a leakage of  ~93 uA    then  the  .48 (the reading  of number 4 before pressing the switch) which is a little more than twice the .23 reading then the leakage of number 4 is a little more than ~93  uA    X   2     or a little more than ~186  uA.   

So according  to the article  a leakage of ~200 uA  "happens pretty often"  which I guess means a leakage of ~200 uA would be  acceptable if the gain were higher but here the gain is 35-38 which is way low if the desirable gains are 70 to 100  for Q1  and  90 to 130  for Q2.

Am I understanding the calculation of leakage correctly ?    Thanks.

[LucifersTrip]

Am I understanding the calculation of leakage correctly ?    Thanks.

yes, you got it....

to be more accurate, you can work it out again from the example:
(93uA)*(2472) = .229V

therefore 93uA = .229v / 2472

uA = v before button push / 2472

so, you have .48v / 2472 = 194uA

[Rick899]

I see. More accurate and actually simpler .... So you just divide the reading before pressing the switch by 2472?  Is that right ?   Is 2472 a constant which is used in every case?    Thanks for your patience in helping me get this concept.

[LucifersTrip]

I see. More accurate and actually simpler .... So you just divide the reading before pressing the switch by 2472?  Is that right ?   Is 2472 a constant which is used in every case?    Thanks for your patience in helping me get this concept.

no problem...the answer is in the pic. look at the resistor you're measuring the voltage across