Yes... A Fuzz Face question!!!

[Govmnt_Lacky]

Fuzz masters,

I have just breadboarded a typical fuzz face circuit based on the Tonepad circuit with the resistor values listed on the layout. I also used a 0.01 film cap. For the electrolytics, I used some NOS military grade 2.2uF and a 20uF cap. I also used some choice NOS RCA 2N217 PNP transistors which measured 80/110 with low leakage.
I also incorporated a voltage inverter circuit using a 7660 chip.

So, my problem is that I get barely any response from the fuzz pot. it has almost no effect on the amount of fuzz. The circuit itself sounds like a mild overdrive when the pots are maxed.

I suspect that the 20uF cap in parallel with the fuzz pot may be bad. Could this cause the lack of fuzz and non-response from the fuzz pot? If not, where else can I look?

BTW... I set the voltage on Q2 collector to -4.5V with a trimmer.

Thank you fuzz masters 

[LucifersTrip]

I have just breadboarded a typical fuzz face circuit based...
I also incorporated a voltage inverter circuit using a 7660 chip.

So, my problem is that I get barely any response from the fuzz pot. it has almost no effect on the amount of fuzz.

I suspect that the 20uF cap in parallel with the fuzz pot may be bad. Could this cause the lack of fuzz and non-response from the fuzz pot? If not, where else can I look?

BTW... I set the voltage on Q2 collector to -4.5V with a trimmer.

Even though Q2C set to -4.5V, still need to see that the other voltages are correct.

If breadboarded, can't you test your theory and swap out the 20uF in 10 secs?

Did you try it without the inverter circuit?

[Govmnt_Lacky]

Sorry LT.... Forgive my bad manners 

Input to circuit: -8.98 (from voltage inverter)

Q1:

E : 0V
B : -0.11
C : -0.49

Q2:

E : -0.38
B : -0.49
C : -4.93

These were taken with both pots at 12 o'clock.

[John Lyons]

Q1 collector should be about twice that voltage I believe

[Govmnt_Lacky]

Ok...

After careful inspection..... It appears that I have just fallen victim to the resistor color coding blunder 

My 33K resistor coming off the collector of Q1 and base of Q2 appears to read orange, orange, ORANGE!!!!! (330K)

Damnit! And I don't have any resistor here right now!! 

[Govmnt_Lacky]

It appears that I was initially correct. The resistor measures 33K. I also checked all other components and they are proper resistance, capacitance, etc.

Which still leaves me with a low voltage on Q1 collector / Q2 base! Suspecting bad transistors 

When I lift the 33K at the transistor junction, I measure -1.12V at the resistor. Swapping transistors does not improve voltages.

Gotta wait till tomorrow to try new transistors 

[pinkjimiphoton]

bro, this may sound crazy, but try flipping the trannys. sometimes  i swear fuzz faces seem to work better with the transistors BACKWARDS.
i've been meaning to ask someone why it works like that sometime!!!

[Govmnt_Lacky]

bro, this may sound crazy, but try flipping the trannys. sometimes  i swear fuzz faces seem to work better with the transistors BACKWARDS.
i've been meaning to ask someone why it works like that sometime!!!

Well, I am pretty sure that the transistor I have in Q1 is bad. I think my Q2 transistor is still good. I just don't want to take the chance of damaging my good one. I have some other pieces in my office. I am gonna try them and see where I get before trying any experiments.

[Govmnt_Lacky]

Turns out that it WAS the 20uF cap on the fuzz pot! 

Swapped it out with another 22uF cap and I was fuzzing away and the pots were fully adjustable!!

All of the resistors are Allen Bradleys so the color code for the 33K was correct in the first place.

Something odd though.... I am still getting around 0.50V on the Collector of Q1 

Works and sounds GREAT... just odd voltages. OH WELL!! 

[LucifersTrip]

Something odd though.... I am still getting around 0.50V on the Collector of Q1  

Works and sounds GREAT... just odd voltages. OH WELL!!  

my guess is that you measured wrong (prob not) or could get it to sound even better if the voltages were closer to the classic

[Govmnt_Lacky]

my guess is that you measured wrong (prob not) or could get it to sound even better if the voltages were closer to the classic

I thought about that too. I tried 3 different matched sets of PNP Germs in the circuit, I tried bypassing the voltage inverter, and I tried swapping multiple values in the circuit.... everything I tried did NOTHING to change the 0.50V that I measured on Q1 Collector 

The only piece I did not swap was the breadboard! 

[LucifersTrip]

my guess is that you measured wrong (prob not) or could get it to sound even better if the voltages were closer to the classic

I thought about that too. I tried 3 different matched sets of PNP Germs in the circuit, I tried bypassing the voltage inverter, and I tried swapping multiple values in the circuit.... everything I tried did NOTHING to change the 0.50V that I measured on Q1 Collector 

I just measured the voltages on one of my excellent sounding ge FF's (2N1000/2N1302 in the classic hfe range) and I got pretty damn close to what you have

         e   b    c
Q1 -   0, .1, .6
Q2 - .45, .6, 4.5

Mine has a full, rich saturated fuzz and very good sustain...

Though, you can easily increase Q1C by lowering the 33K....which I tried now just for the helluvit...crap. As I raised raised Q1C (I was able to go over 1V), the tone got progressively thinner, weaker with a large increase in clicky pick percussion.

So, I wouldn't worry about it...not all transistors are created equal..

[Chris Brown]

my guess is that you measured wrong (prob not) or could get it to sound even better if the voltages were closer to the classic

I thought about that too. I tried 3 different matched sets of PNP Germs in the circuit, I tried bypassing the voltage inverter, and I tried swapping multiple values in the circuit.... everything I tried did NOTHING to change the 0.50V that I measured on Q1 Collector 

I just measured the voltages on one of my excellent sounding ge FF's (2N1000/2N1302 in the classic hfe range) and I got pretty damn close to what you have

         e   b    c
Q1 -   0, .1, .6
Q2 - .45, .6, 4.5

Mine has a full, rich saturated fuzz and very good sustain...

Though, you can easily increase Q1C by lowering the 33K....which I tried now just for the helluvit...crap. As I raised raised Q1C (I was able to go over 1V), the tone got progressively thinner, weaker with a large increase in clicky pick percussion.

So, I wouldn't worry about it...not all transistors are created equal..

When someone posts voltages that they consider "good" or the voltages from an original unit I add it to a spreadsheet.... anyway from a sample of 10 ge fuzz faces I got this as the average... people's "good" ge fuzzes are consistently close to these numbers:

q1c: 0.578   
q1b: 0.1      

q2c: 4.51
q2b: 0.578   
q2e: 0.447

with lower gain transistors the q1c is consistently .7+ ... original units q1c seems to be reported as measuring .5 or less.

[LucifersTrip]

I just measured the voltages on one of my excellent sounding ge FF's (2N1000/2N1302 in the classic hfe range) and I got pretty damn close to what you have

         e   b    c
Q1 -   0, .1, .6
Q2 - .45, .6, 4.5

When someone posts voltages that they consider "good" or the voltages from an original unit I add it to a spreadsheet.... anyway from a sample of 10 ge fuzz faces I got this as the average... people's "good" ge fuzzes are consistently close to these numbers:

q1c: 0.578   
q1b: 0.1      

q2c: 4.51
q2b: 0.578   
q2e: 0.447

that's totally great!  an average of many is totally useful. it looks like i'm right on the money...

with lower gain transistors the q1c is consistently .7+ ... original units q1c seems to be reported as measuring .5 or less.

so, you'd prob get .5V with higher gain...unless it's leakage. I'll do more tests on the next one.

[Chris Brown]

so, you'd prob get .5V with higher gain...unless it's leakage. I'll do more tests on the next one.

From what I've seen higher gain q1 == lower collector voltage and lower gain q1 == higher collector voltage. It would be interesting to see how leakage affects the readings... I always try to put a low leakage q1 to keep everything stable but perhaps leaky q1 is the reason for the low q1c voltage reported for the original units.

My experience with leaky q1 transistors is that I get to the gig and it's mushy or muddy...  - kind of off topic but - ...this actually led me to start biasing my fuzzes q2 to around 4.75v at around 78F degrees instead of 4.5ish at 70F.... now I do this with all of my gig units regardless of leakage... seems like most stages are hotter than the air conditioner at home on the electronics bench. Even with an external bias I build the unit so that when the bias control is in the middle it's getting 4.75ish volts at hot room temperature... somewhere 78F-80F.  Seems more consistent from venue to venue and gets the "4.5 at 70F" sound even thought it's not always 70 degrees... It's a balance or a compromise.

Anyway, I diverged.

Sounds like your voltages are pretty close to the norm for really good fuzz.

[LucifersTrip]

From what I've seen higher gain q1 == lower collector voltage and lower gain q1 == higher collector voltage. It would be interesting to see how leakage affects the readings... I always try to put a low leakage q1 to keep everything stable but perhaps leaky q1 is the reason for the low q1c voltage reported for the original units.

actually, if you think about it, the leakage subtracts from the gain, so if you're right above, then higher leakage = lower gain = higher collector voltage....that's if you're comparing two transistors with the same gain and one has higher leakage. the net gain of the one with higher leakage is lower.

but the difficult question is, what's the difference if the net gain is the same but the leakages are different?

remember the RG test:
http://www.geofex.com/Article_Folders/ffselect.htm

Lets say you put a Q1 candidate in there and you read .3v (leak), then push the button and it reads 1.1v = net gain 1.1 - .3 = 80 hfe

then you put another Q1 in there and you read .2v (leak), then push the button and it reads 1v = net gain 1 - .2 = 80 hfe