Home Forums GuitarPCB Build Support MKC3 gain (old thread)

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  • #1452
    Anonymous
    Inactive

    Hello

    I have built an MKC3 and have a problem: it responds in a peculiar way to the gain knob.

    At very low settings it sounds very close to a BYOC Klon clone in a direct comparison. So having compared I also have realistic expectations for the max gain.

    When increasing the gain nothing much happens until at very high settings, treble is attenuated.

    The pedal is built without options and with the stereo pot for gain.

    IC voltage readings. I do have a crappy voltmeter but hopefully it is sufficient for fault tracing purposes.

    Source measured over “GND” and “+9V” on the PCB: 9,24V

    Pin     IC1   IC2

    1       4,63   4,61

    2       4,63   4,64

    3       1,3   4,58  (both these readings seem suspicious)

    4       0      0

    5       4,53   4,59

    6       4,63   4,64

    7       4,67   4,67

    8       9,25  9,26

    I also tried swapping the ICs and got similar readings in IC1 socket after swapping

    I enclose an image if that may help. I was a little confused with the pinning for the gain pot. Blue is pin 1 and orange is pin 3 for all pots.

    Best regards. /Målberg

    #1455
    Barry
    Keymaster

    I would follow the usual troubleshooting ideas listed in the tips tricks and tutorials section of the forum which would include checking all values by code and verify orientation and re-flowing all solder joints. Since this is a complex build an audio probe may also prove useful to narrow down the list of suspects quickly.

    Here is a proper breakdown of the correct voltages and audio path.

     

     

    #1456
    Anonymous
    Inactive

    Thank you for the Swift response. I have double checked resistances, even though I have to admit that it is difficult to du unambiguously for the ones that have brown stripes at both ends.

    I have also checked orientations.

    I am a wee bit uncertain re capacitors. Perhaps someone could check the image for obvious errors?

    Was I correct to wire pot pin 1 to 1 on the PCB?

    I do not have or know how to use an audio probe so next step is re-soldering I guess.

    Best regards /Målberg

    #1458
    wilkie1
    Moderator

    +1 Barry.  The voltage at pin 3 of IC1 is obviously too low.  I suggest removing power and the ICs then resolder all joints.  Particularly pay attention to pin 3 of the socket of IC1.

    #1467
    Anonymous
    Inactive

    Reflowed Soldier joints. No change.

    I built a simple audio probe (internet is your friend). The readings are enclosed.

    I noted each component following each signal path.

    I measured on both sides on each component, where possible.

    x means no signal

    Check means signal. Where the signal was particularly weak I noted that with a comment.

    All measurements were taken with effect on and all controls at 12:00.

    C5 is not mounted so those measurements are taken at the empty terminals.

    it seems that the area between R15 and IC2 is cause for concern.

    Best regards /Målberg

    #1469
    Barry
    Keymaster

    If you go to our Tips Tricks and Tutorials section of the forum and under Build Guides. (also available from the Home Page as a large green button) you will see a multitude of important guides listed in a row.

    Here is the direct link: https://guitarpcb.com/forums/topic/pedal-building-guides-mandatory-reading/

    Once there we have an Audio Probe Explained guide. This may be helpful depending on what you found on the internet.

    #1470
    wilkie1
    Moderator

    From your measurements, it appears that you have bad connections from R15 through to R21.  I suggest you remove power and both ICs.  Then resolder all pads around R15, IC2 and R21.

    Also, look closely to make sure there are no solder bridges that are causing shorts between traces on the board in those areas.

    Also resolder all connections on the pots and their wires to the board.  Resolder both sides of R3 and pin3 of IC1.  Remeasure the voltage at pin 3 of IC1.  It needs to be around 4.5V.

    #1471
    Anonymous
    Inactive

    Thank you for your patience. I have successfully completed a few pedals before but fault tracing is not my forte. I had missed the audio probe guide. Will check that out, repeat the resoldering and, hopefully, get back with success.

    #3781
    Andreas
    Participant

    Where you successfull? Did you have found the error? Was it the D2? I have also soldered the MKC and it doesn’t work. Maybe the installed D2 and R25 is the problem, because i use that with the 3DPT handy board.

     

    #3782
    Barry
    Keymaster

    @ Andreas

    Many people do not respond once they have solved unfortunately. This thread is from August.

    Please start your own thread with everything we need. Check voltages and report with your finding as well as photos. It only adds confusion when jumping on an old thread.

    Your problem is likely a completely different issue and has nothing to do with D2 or wiring board.

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