Home Forums GuitarPCB Build Support Micro amp problem (solved)

This topic contains 20 replies, has 4 voices, and was last updated by  Knallkopf 2 months ago.

Viewing 15 posts - 1 through 15 (of 21 total)
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  • #3500

    Diederik
    Participant

    Hello,

    i’ve built the Emexar micro amp version. The led works, i’ve got signal. But in effectmode there is no boost and the volume works counterclockwise.

    what did i do wrong?

     

    #3501

    wilkie1
    Moderator

    The volume pot is wired backwards.  Reverse the wires to lug 1 and 3.  Do this at the pot, not on the board.

    Now that you have the board removed to fix the pot, send us a better photo of the front and one of the back. If you have no boost, you may have a resistor value wrong.  Check all of them.  Let us know the results.

    #3503

    Diederik
    Participant

    #3504

    Diederik
    Participant

    #3518

    Barry
    Keymaster

    An Audio Probe would make very quick work of your problem and benefit all future troubleshooting.

    See the GUIDES page for more on Audio Probes.

    For now here is a photo with proper voltages. Please update us with yours.

    Also it clearly shows the Audio Path for testing.

    #3522

    Barry
    Keymaster

    “Tack solder” a jumper (short wire or leftover resistor lead) connecting both the anode and cathode sides of R10 (currently a diode) together and see what happens.

    #3544

    Diederik
    Participant

    Now I read following voltages on the ic from pin 1 to pin 8:

    0,1465

    4,506

    2,255

    0

    0,1464

    4,506

    9,027

    0,0001

    Still no volume boost….

    #3548

    Barry
    Keymaster

    Your pin 3 voltage is low. It should be 4v.

    Most importantly:

    I cannot clearly see the entire board. Update with a clear new board photo.

    Because I cannot see everything please check that you followed these instructions from the build document for the MA build:

    ● The MicroAmp only has a single Level control. If you wish to keep your build true to the original, we suggest using a hand wired potentiometer connected to the “Gain” pads so you can center the single knob on your enclosure. If you do this, you will need to solder a fixed 10k resistor between “Volume” pads 1 and 2, and a jumper between pads 2 and 3.

    #3549

    Diederik
    Participant

    I measured all the resistors. They are the right value and in the right place. I reflowed the solder. Pin 3 Still measurs 2,5 volt.

    Capacitors should also be correct.

    I use the volume slots, not the gain. Kit is from Musikding and the hole in the predrilled enclosure is offset. That’s why.

     

    #3550

    Barry
    Keymaster

    The pot needs to be in the Gain pads. Also you need to have a 10K resistor and a jumper in the volume (level) pads per the directions.

    Whether you hand wired the pot or not it does not matter you still need to do what the final directions say above. The pot must be in the gain pads and you need to solder a fixed 10k resistor between “Volume” pads 1 and 2, and a jumper between pads 2 and 3.

    This is why I was asking for an updated picture because I cannot see what is happening.

    #3551

    Diederik
    Participant

    #3552

    Diederik
    Participant

    I Still have to change the pot to the gain side

    #3554

    Barry
    Keymaster
    • The potis must be used in the Gain pads and you must:
    • solder a fixed 10k resistor between “Volume” pads 1 and 2,
    • and you must place a small jumper between “Volume” pads 2 and 3.

     

     

    Then you will still need to make the connection from VB to IC3 in Purple above.

    This can be done on the back side of the board best IMHO.

    If it helps I think we are very close now.

    #3568

    Diederik
    Participant

    Thanks for all the help. I got it working now. Apparently, the resistors and jumper in the volume slots are a “have to”, not a “want to”. Volume boost starts on the last 2 millimeters of the pot. Is that normal? If so, would a lineair pot help solve this?

    #3571

    Barry
    Keymaster

    “Want to” in my tongue means you must in a nice manner or we would say it is optional.

    In other words if you take that pill you will want to eat first.

    I completely understand so that is why I was extra clear with you. My daughter speaks German which was my next move.

    That said congrats and you are welcome to try a different taper pot. We simply chose what the manufacturer did but we always encourage experimentation.

    Also note that the Micro Amp is more of a Mod based on the more popular circuit varieties since it was so close schematically the Mod was too easy to pass up. That said all of our other builds are much more “straight forward”.

    I am glad I have helped and you have a working circuit.

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