Home Forums GuitarPCB Build Support Dr Phybe – (solved)

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    I tried to check this alone, I welded all the points again to avoid the failed welds … I checked the cabling of 3pdt with the guide but I can not find the solution to my problem.

    Whether the effect is activated or not, there is a clear sound with no flanger effect. I suspect that I have probably missed something. Here are some pictures that I hope you will understand better than me.

    I did not saw what is the purpose of tr1 in the doc, must it be adjusted?

    Thank you for your help.



    The trimmer needs to be adjusted to find the “sweet spot” where phasing occurs.  Slowly advance the trimmer while sending a signal through the pedal.  You should get phasing somewhere around the middle of rotation.  Set it for the maximum effect.


    Hi wilkie1

    I tried to play with the trim pot but nothing as changed. I did something wrong… It’s a 250k like in the documentation and fets are matched pairs from gpcb.

    Ic3 and IC1 are correctly plugged?


    And I used a bc557b -h41 instead of a 2n4125 for Q5 (the shop where I bought it said it’s the good remplacement part because he won’t have a 2n4125 for now). Is it right?


    If you have a DMM (Digital Multimeter), Measure and report the voltages on all IC pins and your voltage at +9V pad.


    Ok, I did it:

    • Voltage input: 8.9V
    • Speed: Max Pot
    • SW1:On

    IC1: TL071
    1.  0.14
    2.  4.49
    3.  3.03
    4.  0.0
    5.  0.0
    6.  8.89
    7.  4.49
    8.  0.14

    IC2: TL074
    1. 4.5
    2. 4.50 ~ 4.51
    3.  4.48 ~ 4.49
    4.  8.89 ~ 8.9
    5.  4.48 ~ 4.49
    6.  4.49
    7.  4.49
    8. 4.48
    9.  4.49
    10. 4.49
    11. 0.0
    12. 4.48
    13. 4.49
    14. 4.5

    IC3: TL061
    1.  0.02
    2.  4.41 ~ 4.62
    3.  3.86 ~ 3.87
    4.  0.0
    5.  0.0
    6.  8.83
    7.  4.6 ~ 4.83
    8.  0.01 ~ 0.02

    Q1- Q4: 2N5952

    1. 4.3 ~ 4.42
    2. 4.49
    3. 4.49

    Q5: bc557 instead of 2N4125

    1. 4.49
    2. 3.96
    3. 2.04



    I think you have the IC legs numbered incorrectly.  Read this and provide new measurements.  Particularly, look for a varying voltage on IC3 pin 6.  Reduce the speed pot to 50% to see this more easily.

    I am looking for a varying voltage that will indicate that the LFO is operating.


    Oups sorry I was wrong with pin numbers…

    I did that measurements with the speed pot approximatively at 50%.

    Thank you wilkie1 ! 🙂


    OK.  I think you can measure a varying voltage at lug 2 (or the middle pad ) of the Rate pot (P1).  If so, Measure the voltage at any of the Gates of Q1-Q4.  IF the voltage is steady there, slowly adjust the Trimmer.  At some point , you should see the voltage at the gate start to vary.  Adjust the trimmer to get the maximum variance.  Now you should hear phasing with a guitar signal applied.  If not, tell us where you lost the varying voltage.


    Check the BC557 has the same pinout as the 2N4125


    Check the BC557 has the same pinout as the 2N4125


    You are right Billy, I´ve found this:

    I turned it to other way, plugged amp and guitar.

    nothing has changed. I tried to turn the trimmer-pot slowly to find a dephasing, like wilkie1 said, nothing too.

    I’ll take measurement tomorrow evening.




    Since this is a complex build including an LFO I would like to mention that this is an excellent opportunity to use an Audio Probe to quickly check the signal path not only confirming audibly the LFO but seriously narrowing down the area of the board to focus on where the Audio Path check would reveal a fault. Voltages will reveal that the LFO is working and much more but an Audio Probe is also an invaluable tool for listening for where the fault lies and helps beginners solve issues.

    Be sure to always make sure the Pot is full Clockwise when testing for phasing as a SLOW phase might be inaudible.

    Still provide test results please for Wilkie.


    The transistor pinout was just a heads up as Barry says an audio probe is definitely a good option

    Wilkies got it covered! to make it a little easier for diagnosis you should label the transistor pins as

    C B E (Q5) and D G S (Q1 – 4) instead of 1,2,3



    +1 to Barry and Billy!  SInce he indicated that he had clean signal in both foot switch position, I assume that the audio path is complete and functioning although without the phasing.  The varying voltage on IC3 tells me that the LFO is oscillating.  It seems he is losing that varying voltage somewhere between IC3 and the Gates of the FETs.  I agree that the audio probe will make identification of the phasing easier to identify.

    If the voltage coming from the trimmer to the gates is greater than the LFO voltage, there will be no oscillation at the gates and no phasing.  We shall see what he reports.


    R23 looks like a 3K9 instead of a 3M9

    • Hello,

    thank you all, I will take a look later on it, because it’s 23:00 pm here and we have like 38 degrees celcius at home :-)) I m like a fried chicken on my desk 🙂



    Good eyes, Billy!  I think R23 should be color coded ORANGE, WHITE, GREEN, BROWN, BROWN  which would be 3M9.

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