The Face Germanium - Fuzz kit : cant reach bias voltage under 6.6V with trimpot

  • Hi,

    O.k, Solder Joint´s and component Values and directions seem´s to be o.k.
    On shematics the Trimpot is not drawn in,just R5.

    I would reccomend to replace R5 with the original Value like before and look if Q2 and Q1 Voltages change back to the -6.6 ?! V

    Transistors are AC125? i think? with Kit you got one with c.a hfe 80 for Q1 and one with c.a hfe 120 for Q2 right? if so,are they on right Places?


    regards,
    Micha

  • Ok i will replace R5 and resolder all :)
    transistors are AC128. I did not get the idea to mark their hfe, i will look how to mesure it (so i dont know if they are in rigght place. I tried to swap them before the R5 modifications and dont remember a bias difference (sure i did not manage to get -4.5V)
    thanks

  • ok maybe i got a clue
    I did test (hope i dit it well : I placed Q in the transistors places on PNP position with legs on ther name and positiion HFE) cf picture

    Q2 : HFE changes with time (normal?) around 250
    Q1 : stays at 0 : means he s out of order? (could explain the problem, just dont know how he has died since it s far from my r5 soldes and other solders...

    so i wait before switching R5. If Q1 is dead will try first to get a new one..
    .

  • With a Multimeter you can´t measure a germanium Transistor right,that´s why Q2 show´s you a hfe of 240 and not the right value of 45 to 175 !
    but 0 at Q1 is not what i expected on that,maybe it is really defekt but i can´t be safe on that,I don´t trust those Test on your Multimeter.

    For those measures, a Component Tester will be the right choice! :

    https://www.amazon.de/Multifunktiona…la-837350962233

    If you will build more than one Pedal this is a good investigation.

    before you stuck in new Transistors,please measure Voltage on each Pin of your Transistor Socket´s to avoid High Voltages and Damages to it.
    If you solder anything on PCB pls.pull Transistors out cause the heat.

    if you don´t get an AC128,you can try similar PNP Germanium transistors whith the right hfe value for Q1 80 to 90 and Q2 100 to 120

    You also can test ! it with silikon PNP Types they are not so expensive for experiment´s than germaniums.

    On Side one of this thread there´s a link to electrosmash Site with Fuzz Face Analysis,please read and try to understand this helpfull Article.

    Maybe this also helpful: http://diy.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm
    http://www.geofex.com/Article_Folders/fuzzface/fffram.htm

    Einmal editiert, zuletzt von Hendrixianer (16. März 2021 um 15:57)

  • ok i did buy the transistor tester, i aim to

    1) fix this pedal
    2) go on to make my "vintage" pedalboard (screamer kit awaits at home and if i find good kits and have the skill a wah wah, a reverb and maybe a delay. But we are far from that with a non working fuzz lol

    i wait the tester and we ll see if i did burn a transistor (dont know why i didnt took it away from pcb while desoldering, i allways did when i was constructing the pedal)

    i chose germanium to get the closer of hendrix fuzz....but maybe my ear wont ear a difference with silicone. Aniway i got he germanium pcb so i think i have to stick with germanium, dont i?

    thanks again! have a nice day

  • Hello, sorry for the delay.

    It took time to receive the tester and then i have been very busy

    anyway here are the teste for the two AC128

    It seems ok, doest it? even if HFE are not near 80 for Q1 and near 120 for Q2 (i got 95 and 107)

    Do you have any clue so i could fix? (Ac128 are still out of stock so i cant buy new ones)

    thanks and have a nice sunny day ! :)

  • Hello all and thanks again for helping me :)

    hendrinxianer : good if transistors are ok, i will put them at best place Q1 or Q2 now that i got their HFE.

    To sum up the problem (for me also it s long, i recap for me too :) ) :
    Initially the pedal worked but i couldnt reach bias boltage under 6.6V with trimpot

    I replaced R5 (1k) with a 4.7k. It s the resistor before the 10k trimmer resistor of Q2. The goal was to improve the Q2 bias ajustement
    Now the pedal does not work anymore Q2 is allways 8.5 V (as the battery), Turning the trimpot doesnt change Q2

    Here are answers to questions

    • Common of your Multimeter on Batt. Plus, Red-Stripe on Collector of Q2?

    and nothing change without Transistor,while you turn the Trimpot?
    yes -8.78 V., nothing change while turning trimpot

    • What resistance do you have from collektor to Minus of Battery?Did it change while turning Trimpot? Trimpot o.k??

    Resistance from collector of Q2 to minus battery vary with trimpod from 4,5k ohms to 10.5k ohms

    • You can measure your Trimpot Resistance ! between Lug 1&2 turn it and look if Resistance change,and Lug 2&3 as same.

    R between 1 and 2 vary from 0 to 8.5 k ohms
    R between 2 and 3 vary from 0 to 10.7 k ohms

    you (hendrixianer) conlcued : trimpot was ok, Joint´s and component Values and directions seem´s to be o.k


    smellslikebleach : hong potientometers is a brand? i dont know which brands they are, i used the fuzz kit



    PS i dont manage to unscrew the pots (i used a special idiot glue idea...)

  • Yep. Hongh is a Brand. There should be a stamp/ branding on the back of the pot, saying Alpha or Hongh. If you have Hongh you should consider to change all you pots with alphas. In this case you also have the chance to fix you stupid glued pot idea :D

  • O.k,first,get the 6,6V out of Your Head,second,there must be something going wrong with your changes,take the shematic and measure all traces from component to component (Measures on the upside of PCB !),if theem are all o.k.
    What about your Wiring?,by solder out R5 did you desolder and resolder anything of the wires? or is there a Bad /false Contact?

    What Voltages actually on Both Transistors C,B,E?

  • take the shematic and measure all traces from component to component (Measures on the upside of PCB !), (you mean measure if there is a connection, no V or A ? because otherwise i have to resoledier wires before)

    What about your Wiring?,by solder out R5 did you desolder and resolder anything of the wires? or is there a Bad /false Contact? i did desoldier and resoldier the pots wire to gain access to the pcb, i checked the soldier after that, i will redo it


    What Voltages actually on Both Transistors C,B,E?
    will measure as soon as possible (voltmetre is not at home now)

    will also redo pictures

    really dont undestand with all the care i took, im about to take a new kit if we dont find anything :(

    thanks for your help !

  • Hi, all connections seems good (they all sound on the tester)...

    i'm fed up with not founding any errors

    i will remove all from the box (if i manage to remove my "glued" jacks and reorder a kit......

    • Do you have advices for the new one ? better quality components than in kit?
    • is my wiring diagram ok (since i made few changes like not wiring dc jack and trying to make a true bypass pedal)

    THANKS A LOT FOR YOUR HELP AND PATIENCE

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