Classic Bass Preamp - Preamp kit

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    • Classic Bass Preamp - Preamp kit

      Hi guys, thanks for all the contibution you are making in this forum. So, I put together a musikding kit of the classic stingray preamp, but i cannot make it work, so i'm reaching to you to find some help.

      First, I'm not very competent about electronics, but I'm trying to learn. Please be patient, consider my competence at "hairless monkey soldering stuff" level. :D

      That's the situation:

      I'm using a bartolini mm4cbc wired in parallel, with an impedance of 1.95K. (3.9 each coil). I can read on a multimeter the correct impedence, so i'm assuming it's wired correctly and working (i was using it before the preamp project.

      First wierd thing, the audio output is very low, and it's al the same level if I take out the battery (is it even possible?!)

      So far, I did the following:

      1) i checked the battery, it's working fine (8.8 V);
      2) I can see the same V on the board input, so no bad cable
      3) I can see the same V between pin 7 and pin 4 of the op-amp

      So I'm guessing the op-amp is powered, but it seems not amplifiyng anything.

      What should I check next? Do you have a step by step procedure to toubleshoot your device when it doesn't work? Have you ever experienced something like this?
      What connection should I check on the PCB, what should i read on the multimeter to check anything and how I can test the audio path?

      Thank you very much for your help and time!
    • Hi cebersp, Thanks for your reply! Here some photos:

      a) the schematics, as it is on the installation guide

      1) the wiring of the bass and treble pot: Since the bass pot was working in reverse (maybe it was a feature, i'm not sure, i reversed lug 1 & lug 3, so now it's working in a traditional manner, the treble pot is connected as specified in the installetion guide.

      2) the board. Since you have to install some resistor in a vertical way, i'm not sure if to proper function they have to make contact with the upper side of the board, i frankly don't know. Might it be an issue? it's well soldered in the bottom side

      3) the wiring on the volume pot. On pot 3 there is the output from the board (lug 3), the white cloth wire is the output (lug 2), on lug 1 it's the output ground from the board with the brown wire that switch the preamp off when the cable is disconnected, that goes to the ring of the jack with the black cloth wire.

      Hope it helps,

      Thank you very much!
      Images
      • Schematics mm preamp.jpg

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      • 1.jpeg

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      • 2.jpeg

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      • 3.jpeg

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      Files
    • Thanks simon.bethke for your reply. Yeah, it might be that i did something wrong myself, and that the schematic is generally correct. Following your advice, do you suggest to disconnect all the treble pot lugs from the circuit, to see what is going to happen? Or just the lug connected to the op-amp output (it should be lug 1 on treble pot)?

      Thank you very much for your time