Home Forums GuitarPCB Build Support Sunn Model T: Switch Issue (Solved)

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    Hey folks,

    me again having issues/questions with the Sunn Model T. I finally had some time to solder the Musikding kit together and stumbled over two things.

    1) When I want to adjust bias I have strange voltages on Q4. Here’s what I measured (after adjusting the trim pots):

    g: 0
    s: 0.13
    d: 5.02

    g: 0
    s: 0.10
    d: 5.53 (although trim pot was turned completely counter-clockwise)

    g: 0
    s: 0.18
    d: 5.00

    g: 4.93
    s: 5.44
    d: 9.28

    Those last measurements shouldn’t be correct, right? I thought maybe the Q4-J201 is broken, so I changed it but I got the same results! What would be proper voltage values for Q4? And how do I get those?

    2) Both the normal & the brite mode work fine when I switch to the desired channel. But the “Both in” is just silent. Any ideas why this could be the case?

    Thanks again and sorry for my noob-questions!



    Your measurements are correct.  Take a look at the schematic and you will note that the Drain for Q4 is connected directly to the +9V supply.

    The reason your BOTH switch position isn’t working is because you have the switch wired incorrectly.  Consult the build documents for 2 different possible switch wiring guides.  This depends on the brand of switch you have.


    Thanks for your fast reply and clearing up, wilkie!

    I automatically assumed that musikding sends out switches that are identical to the ones from the guiitarpcb shop. I should start measuring everything before opening new threads in the future 😀

    Sorry again for the noob-questions and thanks for your help!


    I just flipped the wiring and everything works perfect! => SOLVED




    Thank you very kindly for reporting back and enjoy your build!

    Not to be too hard on Das Musikding since we put multiple switch pattern diagrams in the Build Document because unfortunatly these switches are harder to come by On/On/On and Datasheets are equally hard to find and often were incorrect anyway so that is why we showed multiple switch patterns. Really no other way around it due to the scarcity of the switch.

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