Ge Fuzz Face troubleshooting

Discussion in 'Burnt Fingers DIY Effects' started by Suede, Jul 18, 2013.

  1. Suede

    Suede TDPRI Member

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    Hi,I've built a Ge FFace using 2 TI 2G308 from Small Bear.The problem is that the effect is producing very low output, well below unity gain - it's about 3dbs lower than when bypassed.
    Now I know Fuzz Faces are notorious for having low output issues but I built another one in the past, that slightly increased the overall volume,especially when on with fuzz pot set to max,without being picky with the transistors, they were rather on the lower hfe side.

    One other problem is that when I turn my fuzz pot down instead of reducing the distortion, it gets very thin and clips my signal, especially on higher frequencies,without having any fuzz on it.It isn't cleaning up as it should, rather farts out instead.Could that mean there is a bad cap?

    Here are the transistor's specs and my circuit voltages:
    Q1: hFE=92, Is=37uA
    Q2: hFE=155, Is=83uA

    Voltages:
    Q1 base : 150mV
    Q1 collector/Q2 base : 0.6V
    Q2 collector : 4.5V
    Q2 emitter : 0.5V

    It looks like it's biased properly and the relatively high hfe of the transistors should result in an increase of output so I'm guessing the problem lies somewhere else.Any ideas greatly appreciated!
     
    Last edited: Jul 18, 2013
  2. poiureza

    poiureza Tele-Holic

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    No precise idea

    However if it clips the signal with fuzz down and it behaves more or less correct with fuzz up, you have a serious problem ...

    I can't see how VbQ1 could be any different from ~0.3V
    It is one Ge voltage drop from ground whatever the rest ...
    The other voltages seems ok

    Is "Is" leakage current ? You have some top specimen then ...
     
  3. Suede

    Suede TDPRI Member

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    Yes, by Is I meant leakage, they are supposed to be top specimens since I paid them top dollar :mad:.

    That's why I'm so bummed about it.I got the other one to work with out of loot no-name transistors (which I gave away to a friend btw :rolleyes: ) and now I bought the good TI ones it isn't performing the way it should..
    Could the potentiometer itself be faulty?Although even in-circuit it measures properly.It really is like behaving completely different when not maxed out.Especially at bends the notes just drown and never get heard.

    Quoting from here : http://www.learnabout-electronics.org/bipolar_junction_transistors_02.php
    ''Transistors made from germanium do have an advantage in some circuits due to the lower forward voltage required between emitter and base (0.15V instead of 0.6V for silicon) to make them begin to conduct.''
     
  4. poiureza

    poiureza Tele-Holic

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    Yes my bad, I don't know what I was thinking ...

    I wouldn't focus on the volume drop. That could be normal

    My best bet is that there's something wrong at the Q2 emitter node.
    Sounds like the cap is not located where it should. You sure it's not connected to lug#3 instead of the central wiper #2 ?
    Does Ve Q2 change when you sweep the fuzz pot ?
     
  5. Suede

    Suede TDPRI Member

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    Thank you for helping poiureza :).
    I checked again, the 22uf capacitor at Q2's emitter is wired at the right place (lug 2 of fuzz pot and ground), with the correct orientation too.

    Ve or Vc of Q2 does not change as I sweep the fuzz pot.Smart comment on that one, voltages should change by altering the pot's resistance..
     
  6. poiureza

    poiureza Tele-Holic

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    Err ... no forget that one.
    Voltage should not change. It would only change if the cap was at the wrong place or had the wrong orientation.
    Between Q2 emitter and ground there's always 1K resistance, no matter where the wiper is. The resistance doesn't change for DC bias, it only changes for the AC signal.

    I think the DC circuit is OK.

    But then we're stuck.
    I still think it must be somehow related to the wiring around the 20µF cap

    Did you use the regular resistor values or did you have to tune them ?
     
  7. steve440

    steve440 Tele-Meister

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    Sounds weird, never had one act like that before. Could you take some pictures so we have enough info to be able to trace the circuit visually?
     
  8. Suede

    Suede TDPRI Member

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    Sure I'll take pictures when I borrow a decent camera.The resistors I've used are not the stock values they were recommended by small bear to match the transistors and result in Q2 Vc at 4.5V. They are 24k instead of the 33k, 680 in place of the 330 (shouldn't this result in even higher output on paper?) 9.3k for the 8.2k and 82k at the feedback resistor.
    I'll try to record some sound clips as well to give you a better idea.
     
  9. steve440

    steve440 Tele-Meister

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    Those resistors should work ok.

    Voltages:
    Q1 base : 150mV
    Q1 collector/Q2 base : 0.6V This should be 0v check your connections!!
    Q2 collector : 4.5V
    Q2 emitter : 0.5V
     
  10. steve440

    steve440 Tele-Meister

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    More specifically, check you have q1 collector & q2 base joined together.
     
  11. poiureza

    poiureza Tele-Holic

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    He certainly meant Q1c=0.6V and Q2b=0.6V too (obviously)
    i.e. not the voltage difference between both locations ...
     
  12. steve440

    steve440 Tele-Meister

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    Most would write the voltages like this

    Q1 B 0.15v
    C 0.6v
    E 0v

    Sorry, it wasn't 'obvious' to me during a quick skim over the info. Anyway, once you get off your high horse, see if you can rack your brains and think of a solution to the problem instead of acting like a berk;);)
     
  13. Suede

    Suede TDPRI Member

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    Sorry if I confused you, yes I didn't mean the voltage differential between Q1 collector and Q2 base.All measured voltages were to ground and of course they are absolute readings,they are negative since the circuit is with positive ground.
     
  14. steve440

    steve440 Tele-Meister

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    No worries, get some pics!
     
  15. Suede

    Suede TDPRI Member

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    Here they are, though I'm not sure what someone could see from these:

    [​IMG][​IMG][​IMG][​IMG]


    At the two junctions where one lead seems to be touching another while it shouldn't, I've checked it numerous times with the DMM and it's not making contact.
     
  16. tjk3052

    tjk3052 Tele-Holic

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    [EDIT] I accidentally hit reply before I was done...

    I'm not sure what resistor values you are using, but maybe I'm just reading the bands wrong.

    I think you have your Q1 collector resistor connected to where your Q2 collector resistor should be, and vise versa. The Q1 resistor needs to go from the collector to -9V and the 470ohm resistor. The Q2 resistor need to go the output cap and the other side of the 470ohm resistor. I think you have that backwards???
     
  17. tjk3052

    tjk3052 Tele-Holic

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    This is what I mean. Looks to me you wired it like this?

    Untitled-3.jpg
     
  18. Suede

    Suede TDPRI Member

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    Oh my it was there in my face all along.

    Thanks so much tjk3052 for pointing this out and of course steve and poiureza for scratching your heads because of my dumbness! :oops:
    It's got a fierce sound, quite aggressive for a fuzz face-rather on the higher gain side.

    I'd get you all a beer if I could, now all I can do is record a sample and let you know how it sounds.:D
     
  19. poiureza

    poiureza Tele-Holic

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    Cool :cool:

    Are you going to see Waters on 31 ?
    18€ only :eek:

    Saw him 2 days ago (for the second time), fantastic show.
     
  20. steve440

    steve440 Tele-Meister

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    Busy weekend, just returned. Glad you got it sorted. Good eyes on TJK;)
     
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