Fuzz circuit problems

[thehave]

Hey,
Ive built my first pedal, the fuzz face and Im having a problem. I have an NPN circuit with AC127 NPN transistors, and I used this image to help me build the pedal. I changed it so that the positive +9V lead replaces the black right corner wire at the top left of the image and made the middle red one the ground. I also replaced the 8,2k resistor with a 10K linear bias.


The transistor readings Im getting are:
Q1
C   0.87V
B   0.58V
E    0.00V

Q2
C   9.20V
B   0.85V
E   0.63V

I do have the 33k ohm resistor in place which should drop the voltage at C of Q1 but by only 1.1V?? Ive checked connections but is the whole circuit wrong? 

Thanks for the help!!

[thehave]

Okay I added the 8.2k ohm resistor in series with the 10k pot but still when the pot is fully open the voltage at C of Q2 is 7.30V. Shouldnt it be closer to 4.5-5.0V?

[pinkjimiphoton]

first thought is the vero layout looks kinda funky. make that very funky. as in likely the entire problem i'm sorry to say.
go to tagboardeffects.blogspot.com and look up the fuzzface circuit.
you said you made an npn version with ac127's. cool.
if ya look at a normal fuzzface layout, you'll need to reverse the + and - polarities of the two electros as well as the wires from the battery.

the more i look at that layout, the more i am positive its your entire problem. your power leads in the pic are backwards, too. the fuzz pot is ungrounded... lotta issues mate, be better to start over imho.
when i get back later i'll try and see if i can find a decent fuzzface vero to upload for ya. if somebody else doesn't beat me to it.

[pinkjimiphoton]

try this one. little bigger than i'd layout myself, but its verified and set up for npn use already.

i would socket them transistors. you need specific gain ranges for the ge's to work well in the circuit, and some ge's will just plain not work. i suspect that's also part of your problem.

worst case, try to find a couple si's with gains around 200 or so. adding a small resistor between e and ground will help adjust the gain of the q's.... somewhere in the neighborhood of 220r on q1 and 47r on q2 will drop the gain ranges to where they'll work pretty well, tho ya may need to adjust the values a little bit. this will get ya a good bit of the fuzzface tone, and a little softer like ge's.
also make sure your pinout is right on the q's sometimes depending on manufacturer things are backwards from what ya expect.
frankly, in FF's sometimes reverse beta on one or both q's seems to give a better fuzz. this is a hell of a hard circuit to nail down for a first attempt, but soooooo worthy when ya nail it.

[Guurf2]

Hi,

New here but got a bit of experience with fuzz faces and ac127s.
Check your transistors! I have like 30 ac127s and they gave me a whole lotta trouble before i learned to check them right.
On a FF circuit q1 should have about 10-30 less hfe than q2.
FF's worked for me in combos like q1=50 q2=70 , and also fairly well with q1=90 q2=120 - these will probably give a rather classic fuzz tone (second couple would more, first one worked fine too) also bigger differnces worked for me on Si - q1=200 q2=400 and sounded rather cool.
If q1 has a higher hfe than q2 - that would give you a rather bad sound. Also reccomended that the minimum hfe you use would be higher than ~30.
Second issue for Ge's - Leakage. Iceo should be lower than 0.3ma (on q2 iv'e found that you can have higher leakage and it'll still sound cool but not on q1! q1 should have the lowest leakage you can find).

Im saying this because some of my ac127 had low hfe's and others had super high iceo's so check them good.
Also i would reccomend for a NPN Ge FuzzFace, that you use an ac187s, found them more reliable in hfe and leakage than the ac127s.

Good Luck,

Guy.

[thehave]

Thanks for the answer!! I was thinking that this cant be right and I could start all over.  Its a learning process and I really want to make this work!

Yeah I suspect that the gains on these are a bit too high. Ive heard the AC127 can be rough sounding.. but Ill see when I get the circuit to work.
I have sockets so I can change the transistors then.

Ill be sure to use verified pcb layouts from now on..

How does that 1N914 diode function in the circuit and is it necessary to make this work?

[pinkjimiphoton]

the 1n914 is being used for polarity protection, if ya use the wrong adapter it will shunt the voltage to ground and save the rest of the circuit.

[Electric Warrior]

the more i look at that layout, the more i am positive its your entire problem. your power leads in the pic are backwards, too. the fuzz pot is ungrounded... lotta issues mate, be better to start over imho.

In his first post he said he fixed the power leads. The Fuzz pot does seem to be grounded, but the electrolytic needs to be flipped, no?

Okay I added the 8.2k ohm resistor in series with the 10k pot but still when the pot is fully open the voltage at C of Q2 is 7.30V. Shouldnt it be closer to 4.5-5.0V?

Actually it should be lower than that with Q1C sitting at 0.87V. It looks as if Q1 may be working correctly. You probably got the pinout of Q2 wrong.

Second issue for Ge's - Leakage. Iceo should be lower than 0.3ma (on q2 iv'e found that you can have higher leakage and it'll still sound cool but not on q1! q1 should have the lowest leakage you can find).

No, Q1 should have the right amount of leakage to make it bias well. Too little leakage can be a problem (especially in combination with low gains). Too much as well. But what's too little or too much depends on other specs as well and on how you like the circuit biased.
Q1C voltage is rather high here. If Q1 is working correctly, this may be a case of too little leakage. I'd use a larger resistor on its collector to bring it down to 0.5V or lower. That should put Q2C in a range where I like it as well.

On a FF circuit q1 should have about 10-30 less hfe than q2.
FF's worked for me in combos like q1=50 q2=70 , and also fairly well with q1=90 q2=120 - these will probably give a rather classic fuzz tone (second couple would more, first one worked fine too) also bigger differnces worked for me on Si - q1=200 q2=400 and sounded rather cool.
If q1 has a higher hfe than q2 - that would give you a rather bad sound.

Some like them matched, others prefer them mismatched. Easy enough to try out.

[antonis]

the 1n914 is being used for polarity protection, if ya use the wrong adapter it will shunt the voltage to ground and save the rest of the circuit.

But perhaps not its hide... 

[GibsonGM]

I larger rectifier diode like the 400X series (1N4001....1N4007 etc) may be able to withstand the reverse current and not fry.  I use them because of that, altho I would NEVER reverse my polarity!  (ha ha)