Fuzz Face help needed

[Fenderstrat]

Hey everyone, i recently built a fuzz face and it worked perfectly for a while, but now, well theres a bit to be desired.
here goes the little checklist.  I'm sorry but i'm a bit new at electronics, you might have to dumb some stuff down for me

1. It sort of fuzzes and the volume is only about half or less of what it should be, if i turn the volume pot it seems to have no effect at all. apart from maybe making a bit more hum. if i turn the fuzz pot it has no effect either. I can turn the amp up and it is at a good volume, and fuzzes the sound but it sounds really weak and dull, not any sort of comparison of what it was before.

2.Name of the circuit = Fuzz Face

3.Source of the circuit (URL of schematic or project) = http://www.geofex.com    thats whats in my address bar, you have to click the link to technology of the fuzz face

4.Any modifications to the circuit? I used the circuit schematic with the Roger Mayer mods

5.Any parts substitutions? I couldn't find any 2k pots or 20uF capacitors, so i used a 1k pot and a 22uF cap, thats about it

6.Positive ground to negative ground conversion?ummm.. the ground is connected to the positive?

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => the battery is charged at 9.02 volts


Voltage at the circuit board end of the red battery lead =0.00v (positive is ground)
Voltage at the circuit board end of the black battery lead =9.02v

Transistor Voltages (AC128's)
Q1
C =0.27v
B =0.09v
E =0.00v

Q2
C=8.92v
B=0.28v
E=0.31v



Any help would be much appreciated

Cheers- Rhys

[petemoore]

C =0.27v Low, should be about >1v, test for 33k between C and battery clip
B =0.09v hopefully this one will 'follow'
E =0.00v correct, Gnd.

Q2
C=8.92v High, should be ~4.5v, test for Q2C resistor value to battery clip
B=0.28v  Should be exactly as Q1C, probably is connected.
E=0.31v
  If you used a trimpot, Q2 collector resistance should be...about 8k2 to get somewheres around 4.5v [4k7 or 15k not too uncommon.
  Test all the resistances between transistor pins and ground too, Q2E should have..1k to ground, 100k to Q1 base. 22uf must have it's + side to ground, emitters toward ground, collectors toward top.
  you've got a good schematic, PNP transistors in Pos Gnd. circuit, red wire to Gnd., just look for resistances what's called for, measureing from 'distant' points, that way as many of the connections get checked at the same time.

[Fenderstrat]

Ok, thanks heaps for that. and you just happen to be perfectly correct!  , because last night after being completley stumped as to what the problem was, i tested every single component (caps, resistors pots etc.) and i found that the resistance of the resistors was only about half what it should be. the 33k was only 13k, and the 18k had dropped to 12. the 1k and 100k were still perfect though.    after noticing that i changed them over, and measured the resistors before i put them in. 33k and 18k, as they should be. I soldered them in and measured them, still the right values. after this my fuzz face worked perfectly, for a while.  I woke up this morning eager to use it a bit more! and bang, same problem again. the resistance had dropped back to 12k and 15k.

I have no idea what is going on here, any suggestion would be greatly appreciated

[petemoore]

  Not sure, I've had measurement problems with DMM, I think that was measuring voltages with near dead battery though, not sure if it'll 'off measure' resistances.
  Fixed resistors generally speaking by all accounts don't drift like that, two of them doing it' would make me look at something else common to the measurement process as the cause of the misreads {I think this has to be a misread of some type].
  15k's not bad, I'd check the voltage measurements again and mostly go by that, adjusting Q2C bias resistor to bring 4.5v or 5.5v to the collector with 9v battery.

[Fenderstrat]

I'm positive its not a misread, because not only do the measurements drop, the sound is sacrificed horribly, and when i measure the rest of the resistors they measure fine. the resistors are losing their resistance. thanks for the suggestion, but i don't think thats the problem. maybe i'll just solder in new resistors each time i want to use it?  lol.
Thanks heaps for the help, but i'll just sit here and scratch my head for a while i think

[petemoore]

  take new voltage measurements.
  the resistors are losing their resistance.
  I've never encountered this overnight, only when they get >smoking hot, Then IIRC the resistance went up.  two separate resistors drifting value overnight?  

[oskar]

Ghost in the machine eh?

I've never encountered resistors changing values?!  (By this I don't mean it doesn't occur!)
Did you meassure them after you removed them?
Sounds more like it's one of the transistors being dammaged by heat. Did you use sockets?
Try provoking the circuit with some heat like a blowdryer...

Hi by the way... wonderful place!

[Fenderstrat]

ok, i measured all the transistors and resistors again. both transistors are in sockets, and i haven't been putting the iron anywhere near those resistors, in fact, i haven't touched it at all until just now.  the weather has been quite cold here at night (down to 3 degrees C) the project has been in the shed, which isn't insulated. could this maybe change the resistances?

Q1  C: 5.92v
      B: 0.07v
      E: 0.00

Q2 C: 9.28v
     B:  5.89v
     E: 5.92v

33k resistor=41k
18k resistor=9.8k
1k resistor= 600ohms
100k resistor= 100k


now these resistances are different again from what i measured last time.


Maybe I should just call an exorcist?

[petemoore]

Q1  C: 5.92v
      B: 0.07v
      E: 0.00

Q2 C: 9.28v
     B:  5.89v
     E: 5.92v  This seems high, you are measureing <1k from the transistor E leg and the ground?
  Then from a ground to all other grounds, testing for continuity between all marked ground points?

[oskar]

33k resistor=41k
18k resistor=9.8k
1k resistor= 600ohms
100k resistor= 100k

now these resistances are different again from what i measured last time.

Maybe I should just call an exorcist?

sorry, I've got to ask... you do disconnect the battery before you check the resistance right?
What if you try another transistor?
Swap the first one for a Si?
Either way, do call an exorcist... 

[Fenderstrat]

It's definatley something inside the circuit changing the resistances. I measured the resistors that i took out the other day and their back to what they should be 
and yes oskar i did disconnect the battery.
though, i can't seem to find any exorcists in my area, does anyone know of any?

[oskar]

It's definatley something inside the circuit changing the resistances. I measured the resistors that i took out the other day and their back to what they should be 
and yes oskar i did disconnect the battery.
though, i can't seem to find any exorcists in my area, does anyone know of any?

I've worked with some really hardcore circuitboard maintenance and I've never heard of resistances changing values... (But I'm certainly NOT an expert)
And if they did, from excessive heat etc. it would definitely be a one-way trip. Even with a minimum of components in a construction it really fast
gets hard to meassure your way to the value of single components.
Some errors are rather obvious but rather a lot of them (when you're testing pcb's with a 1000 parts) is file under: ghost 
It really sounds like something is leaking somewhere on your pcb. Things that go leaking would first of all be electrolytic capacitors, when they are
about to go pop!... 
The next set of questions I could think of would be something like. Did you meassure the right board? You're not living under high voltage transmission lines are you? Isn't there a lot of solar activity right now? Is one of your neighbours conducting secret experiments with orgon energy... 
However, if you do have some freaky leak around there, you could eventually see some difference if you'ld turn the potentiometers while meassuring.
Were the transistors new or desoldered from something else?    (transistors? I just don't trust them!)
Sorry there mate, I find it hard to be constructive without actually having the thingo in front of me (as if that would help...)and I'm not gonna bug you with any more obvious
questions. May your all your circuits be successful 

[petemoore]

  I would say it's more likely that the [common to all tests] DMM is playing a trick on all the resistors, than all the resistors at once playing the same trick on the DMM.

[Fenderstrat]

very good point, and your probably right, but it still dosent explain the high voltages on the transistors and terrible sound of my fuzz face 

[petemoore]

but it still dosent explain the high voltages on the transistors and terrible sound of my fuzz face.
  This is still true.
  I don't know what's up with those whacky readings, [fresh battery in DMM?]except that it puts a damper vibe on the debug process, as most readings seem somewhat 'anomolous'.
  the only thing that might still be working it seems is the ratio', it may not give 'indexed' R readings but at least the ratio seems to be close...bigger resistors are reading bigger comparatively to smaller ones.
  WHich makes me wonder where the voltages measured 'are' actually.
  One way to test voltage measurement accuracy, is to connect two series resistors of = value across a fresh tasting battery and see if you get 0.0v [which of course you'll see when measuring voltage across a short wire], 1/2v, [middle of votlage divider] and ~9v [across the battery terminals] at the three possible test points.
  high voltages on the transistors and terrible sound of my fuzz face
  Make measurements across as many connections as possible [distant point measurements], and see what isn't like the schematic.
  I have three DMM's...when one goes to reading whakky, I taste the battery [and replace if it tastes noticably flat] then compare readings taken to those of the other DMM.
 

[hellwood]

ok, i measured all the transistors and resistors again.  the weather has been quite cold here at night (down to 3 degrees C) the project has been in the shed, which isn't insulated. could this maybe change the resistances?

Q1  C: 5.92v
      B: 0.07v
      E: 0.00

Q2 C: 9.28v
     B:  5.89v
     E: 5.92v

33k resistor=41k
18k resistor=9.8k
1k resistor= 600ohms
100k resistor= 100k

bad resistor values like that wont throw your voltages off this bad. you have other issues. make sure the pots, input/outputs, chassis, and any other grounds are all happening for starters. the 2k pot will throw off the bias as well, and yes freezing cold has an effect on resistance (but i dont think that is your problem)

[Fenderstrat]

ok, thanks hellwood. I'm pretty certain I've fixed all the input/output/grounding issues. but i could be wrong.

i've noticed that if the circuit is fully connected (i think its fully connected) the resistor values are stupid 100k= 13k,   33k=12k, 18k= 15k. the 1k resistor seems to have remained normal the entire time. maybe the problem has something to do with that frequency control capacitor ?
The weird thing is that if i disconnect something in the circuit, to make it open, then the resistor values are exactly what they should be.   
so i have a choice of a terrible sounding fuzz face, or one that dosent work at all at the moment 

any ideas?

Cheers- Rhys

[hellwood]

what 1K resistor?

do a diode test on Q2 and make sure its not shorted (if you are 100% sure your pot's chassis are grounded)

[Fenderstrat]

sorry for the late response. I'm talking about the 1k resistor in series with the 0.01uF cap and the 18k resistor.  It's the only resistor in the circuit which isn't reading a different value to what it should be.
The schematic is from the technology of the fuzz face page on geofex. It's the one with the roger mayer mods.

Cheers - Rhys

[Fenderstrat]

hmmm.. it seems im using a 500k linear pot for volume control.     could this be my problem....