EZ Face Problem

[Ag_Nathus]

Ok, so if I can't do an easy face, what can I do? Oh well here we go:

Using the tonepad schematic and layout which I transferred by hand. The Ra resistor is 100 ohms. The Q2 transistor is from small bear and has an Hfe of 146. Now, the bypass works great, but when the pedal is engaged, I get no fuzz. I do get sound though. With the 10K trimpot counter-clockwise I get a clean sound. This diminishes as I rotate the pot clockwise until when it is about halfway then the sound goes away and I get nothing. The 250K and 500K pots act like volume controls and the 100K sounds like a tone control, it goes from a bassier clean sound counter-clockwise to a treblier sound clockwise. Nothing seems to produce any fuzz though. The signal will go just a little above unity gain. Here's some stats:

Battery voltage: 8.9V
Q1 E 8.88
Q1 B 8.24
Q1 C 5.78

With 10K trimpot counter-clockwise:

Q2 E 5.96
Q2 B 5.77
Q2 C 1.38

clockwise:

Q2 E 7.97
Q2 B 7.79
Q2 C 7.96

Here's some pics:

Board:



bottom:



jacks:



pots:



From left to right the pots are 250K Linear, 100K Linear, 500K Audio

Thanks for any help!

Ag

[John Lyons]

Ra should be 1M (1 mega ohm) I beleive.
With 100 ohms there you should not get much if anything out of the circuit.
This resistor is to prevent pops when switch the circuit on and off.

Adjust the trimmer with the black probe of your meter on the collector of Q2 and the red probe on ground.
You want to get around 4-5 volts on the collector.

John

[Ag_Nathus]

Ra should be 1M (1 mega ohm) I beleive.
With 100 ohms there you should not get much if anything out of the circuit.
This resistor is to prevent pops when switch the circuit on and off.

Adjust the trimmer with the black probe of your meter on the collector of Q2 and the red probe on ground.
You want to get around 4-5 volts on the collector.

John

Thanks for the reply. Ok, let me check a couple of things here. On the layout printout at tonepad it says "Joe G:Ra between 100-300 ohm resistor at Q1 emitter just lowers the gain of the transistor, which actually decreases sag because it is driving Q2 less hard, the cool thing..."
That is why I went with the 100 ohm resistor, but you think I should I should go with 1 meg?

Also, they mention that this particular build was modified for negative ground, so would I adjust the trimpot with the red probe on the collector and the black on ground?

Thanks and I apologize for my denseness

AG

[petemoore]

  About 100ohm between emitter and ground, like in YAFF, and works, 1meg wont work at all there.
  The only use for 1megs in a fuzz face would be the pulldown resistors.

[John Lyons]

crap! That's what I get for not looking at the schematic before giving advise!
100 ohms is correct.
I was talking about a pulldown resistor but this circuit does not need one since it has the pregain control connected to ground...

Yes, you want to adjust the trimpot with the red probe on the collector.

Sorry for the confusion.
Are you getting 4-5 volts on the collector now?

John

[Dragonfly]

I havent gone through the layout/schematic yet, but your soldering may have some issues...its hard to tell in the photos, but check your board for any solder bridges in the areas i circled in red....

[Dragonfly]

Also, your voltage readings indicate that there may be a ground issue

[petemoore]

  Yuopp..
  Q1 E 8.88  {IIRC and not off the schematic, this lead should be connected to Ground reference, 0.0v.
Q1 B 8.24
Q1 C 5.78
  The other two should drop when the emitter is grounded.
  This IS a 'regular FF" [PNP Pos Gnd or NPN Neg Gnd. ?]...

[joegagan]

your opamp is way off voltage and your expression loop is disconnected at the base ( medium Q)

[petemoore]

  I'm lost...
  Aq Nathus is referring to 'Q1/Q2' voltages, Joe Gagan is referring to opamps, and the thread title is "EZ Face Problem" ?

[joegagan]

little joke there, sorry to derail....

[$uperpuma]

your opamp is way off voltage and your expression loop is disconnected at the base ( medium Q)

[Ag_Nathus]

Ok, thanks for the slew of replies. Frst off, petemoore, it is a hybrid Si/Ge PNP but converted to negative ground. Second, Dragonfly, that appears to be an optical illusion as a continuity check shows no bridges in those areas (or anywhere else that I can find!) Thirdly, John Lyons, I was able to dial in 4.69 V on Q2 Collector. Here are the new values: Q1 E 9.16 (New Bat), Q1 B 8.53,  Q1 C 6.01. Q2 E 6.21, Q2 B 6.01 and Q2 C 4.69. I am getting fuzz now, but not as much as I expected. From a clean signal, it just makes the guitar gritty, not really fuzzy, so I think there are still errors. Also, I really only get much from the pregain and volume at the extreme high end of their throw, if I turn it down more than a little, the sound goes away. Thanks for the tips so far and let me know if you have any other ideas!

AG

[joegagan]

ok, this has been said before, but you are new, so here goes:

reversing the polarity on pnp fuzzes is iffy and is not recommended. if it isn't too hard at this point, put it all back to pos.ground, then debug as outlined.

[Simon Owen]

I always build mine with Si NPN 2n3904 and Ge NPN AC127, flipping polarity of caps and diodes as appropriate.
It is my favourite diy pedal by far. I recomend adding the pre gain and thickness control at the front and then squeezing in a SWTC before the volume control.
It never sounds bad.

[petemoore]

  MAX1044 voltage converter seems a likely prospect...
  Yupp those Neg. Gnd. PnP FF's....'problematic when so'...
  Not too hard to convert to a Fuzz Face though.

[Ag_Nathus]

Ok, so to make it positive ground, I just flip around the electrolytics and the power connections?

Thanks!

AG

[joegagan]

that is correct

[Tony Forestiere]

Is the 10k resistor at the bottom of pic 1 soldered in?

[Tony Forestiere]

Ooops! My Bad! Br-Bl-Y =100k