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

    This site uses cookies. By continuing to browse this site, you are agreeing to our Cookie Policy.

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

      Hello,

      I finished my pedal and i m very glad of it (1st one). thanks to smellslikebleach’s for its help !

      I took a lot of time, checking the wiring, my solders, put tape for isolation..


      Everything's seems to be ok (light, bypass, jack as switch, non unpleasant sound...)


      But reading about fuzz i found the bias control very important to get the best of it and often 4.5 V a good start.

      Turning the trimpot all the way i can t have less than 6.6 between the red of battery and the collecteur (C) of Q2 (germanium transistor)

      I did few changes on the original diagram but nothing wild (did not connect dc jack, and put the 3pdt wiring shemas of somewhere else). I tried to find the answer on the net but i dont have a clear one,


      Here are my ideas to be able to play with bias and then ge lower than 6.6V, is there a better one to you?

      • Change the trimpot to allow more flexibility to control the bias : but bigger, smaller or same in case of problem on it ? actual is 10k, i can find 25k and 5k. If im right i shoudl put bigger that means 25k

      • change R5 (the resistor in serial with trimpot. Acutal is 1k. I read that some people put 4.7k. It seems more logical to me to change the trimpot but am i right?

      • Change the germanium transistors since they are said to be really inconstent in term of values?
      • other?



      Thanks for your help. I m looking forward to continue with another project (tube screamer) and improve my bias on the fuzz as soon as possible

      have a nice day

      here is my wiring

      The post was edited 1 time, last by roh ().

    • note:
      • For the bias values showed above, the fuzz potentiometer is set to the midpoint (500Ω)
      • The DC voltages might change due to transistor β variations, in this case, we are using a Q1 with β=85 and Q2 with β=120. If you want the see the AC128 PSpice simulation model, check the last part of this article.
      • The important settings to get the best sound out of a Fuzz Face is to have Q1VC=-0.5 to -0.7 and Q2VC=-4.5V. For this purpose, some designers include trimmer resistors to substitute R1 and R3 so the VC of the transistors can be easily adjusted. More info


      electrosmash.com/fuzz-face
      " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "
    • hello, thanks for your answer.
      i read the electrosmah article, that s why i try to setup bias

      • i have a trimmer resistor before Q2. Its a 10ktrimmer + 1k normal resistor.
      • i have Q1VC=0.34V an Q2Vc=6.6V (cant go under, that s my problem)
      • Turing the fuzz buton doesnt change Q2VC
      • I dont know the β of each transistor, i will look how to determinate it


      here where i take Q2VC (in case of measurment error)

      thanks

      The post was edited 1 time, last by roh ().

    • Simply use a Power Supply with lower Voltage :D ;)

      What is the Prob with bias? diddn´t Sound right?

      Hendrixianer wrote:

      The DC voltages might change due to transistor & variations, !!

      roh wrote:

      I dont know the β of each transistor, i will look how to determinate it
      The simple solution is to use a component Tester
      " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "
    • It seems too bright to me but i never uses a fuzz pedal. This DIY is a way to improve my knowledge and my guitar play with new effect. I read everywhere to start around 4.5V and then do the setup with ear. But with 6.6 it seems to be very far and i m nt able to try lower,. That s why i thought i had to change the trimpot or ressitor or transistor

      Thanks for the β, i will look the component tester

      sorry if questions seems really basic, im totally beginner
    • R5 is 1k. if i put a 4.7k parallel it will gives 824 ohms for total r5+new R. That doesn t seems to be a big change before the trimmer

      Dont you mean : put a 4.7k in series with the 10k trimmer to put it from 11k max to 14,7k max?

      thanks for your help, appreciated

      The post was edited 1 time, last by roh ().

    • You could change the trimmer with a normal 10k Pot which give you access to different tonal characteristics.

      Regarding to the highs: welcome to the world of fuzz - some love it some hate it. You could highly influence your tone with the volume and tone pod of your guitar. But the more you increase the gain / fuzz the more the pedal would increase the highs and cut off the lows.

      Try an eq or a mid focused overdrive after your fuzz to bring back mids and lows of your sound.

      The post was edited 1 time, last by smellslikebleach ().

    • roh wrote:

      R5 is 1k. if i put a 4.7k parallel it will gives 824k for total r5+new R. That doesn t seems to be a big change before the trimmer ?( ?( ?(


      Dont you mean : put a 4.7k in series with the 10k trimmer to put it from 11k max to 14,7k max?
      don´t you tell me the R5 is in Series with Trimmer??,when you replace it,you should have 14,7k with R+ TR,you only had to solder it "paralell "on the R in Series with theTrimmer,so you don´t have to solder our R5 for a try.

      i didn´t look at the shematics couse you diddn´t link it.

      so right,try to come to 14- 15 K with R+ Trimmer
      " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "
    • I made a misstype, 1k + 4,7k in parallels gives 0,8k. I mean to put a 4.7k parallel to a 1k doesnt seem to change a lot the value (from 1k to 0.8k)


      Im a little lost (english is not my native language) for the solder thing. But i understood i have to go to 14-15 k with R5 + Trimmer. I will take time later to solder out the 1k to put a new 4,7k


      thanks for your patience


      i dont have shematics, the only i got is the original one with a 8.2k, but they instead put a 1k and a 10k trimmer on the pcb
    • Hello, hope you re doing well

      I finaly tried to improve my bias this morning (receive new resistors + the screamer project)

      I replace R5 (1k) with a 4.7k.
      • I took my time to desolder and resolder (mainly the volume and fuzz pots)
      • i checked the new r5 solder
      • i cheecked every solder i could
      • i checked if transitors were still well in place
      • footswitch works
      • led works when jack is in the input and i use the footswitch


      Q2 is allways8.5 V (as the battery), so i really dont understand what to do
      Turning the trimpot doesnt change Q2

      Do you have any clue? i dont have any im very disapointed

      thanks
    • Hi,

      How did you measure?

      Common of your Multimeter on Batt. Plus, Red-Stripe on Collector of Q2? and nothing change without Transistor,while you turn the Trimpot?

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

      For understanding: Pedal is allright working but sounds bad? than try other Transistors.
      Or Pedal didn´t work?

      Think of that:


      Hendrixianer wrote:

      The DC voltages might change due to transistor β variations,
      regards,
      Micha
      " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "
    • Hello micha and thanks for your help again :)

      here are the answers (just did not test on amp because was afraid, i can do it if there is no fear to dammage something)

      Hendrixianer wrote:

      Hi,

      How did you measure?

      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??
      0,05 V from collector Q2 to minus of battery, doesnt change while turning



      i dont know it trimpot is ok. I tested it on the pcb. when i turn it it changes betwenn feet 1 and 2e and also between 2 and 3. Between 1 and 3 it s allways 0 ohms. I was expecting to find a postition (between 2 and 3) with allways 10K. Is the variaton between 2 and 3 shoud be 10k and that would said trimpot is dead (suprinsing, didnt do anything to it)


      While swicthing the battery on i got same voltage between battery + and feet 1, 2, and 3 from trimpo (8,8 V). Are trimpot brittles (spröde)?





      For understanding: Pedal is allright working but sounds bad? than try other Transistors.
      i didnt try the pedal since the value was very bad. I was afraid to dammage my amp or guitar (no danger)?
      i dont have any others transistors (ac128) and they seems out of stock on the website


      Or Pedal didn´t work?
      didnt plug it to my amp , the footswitch and lights works



      Think of that:


      Hendrixianer wrote:

      The DC voltages might change due to transistor β variations,
      regards,Micha

      The post was edited 3 times, last by roh ().

    • Hi,



      What resistance do you have from collektor to Minus of Battery?Did it change while turning Trimpot? Trimpot o.k??
      0,05 V from collector Q2 to minus of battery, doesnt change while turning


      I mean Resistance in Ohm not Voltage !

      While swicthing the battery on i got same voltage between battery + and feet 1, 2, and 3 from trimpo (8,8 V).

      There must be something wrong ?(

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

      Trimpot´s very sensitive to Heat ! so maybe it is broken or you have a Bad solder Joint elswhere.

      Same to germanium Transistors,to much heat,wrong voltage........Exitus.

      i didnt try the pedal since the value was very bad. I was afraid to dammage my amp or guitar (no danger)?

      There is No Danger for your Amp or your Guitar,you can test but I think it will not work,but try.
      " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "
    • smellslikebleach wrote:

      Standard voltage for Q1 should be around -0,7 V while Q2 should be from -4,5 ill -5,5 V.
      Geht ja darum,das er an Q2 eben nicht auf die 4,5V kommt sondern da die volle Batterie Spannung anliegt :D ,Trotz trimmer und zusätzlichem R,beim drehen des trimmers soll sich die Spannung wohl nicht ändern.
      " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "