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Hi, my Cortado MkII has started to emit a nasty ‘grounding’ buzz. I couldn’t find any loose/bad solder connections on the circuit board or the xlr pins but it goes away if I touch the chassis or metal connectors in my cables with bare skin. This was the only way I could get it to stop. (Also, I plastidipped my piezo so can’t really get in that part to see what’s up.) Any insights into what the problem likely is or how I can diagnose the cause?
You seem to have a bad ground connection somewhere. You can check this by doing a continuity test between pin 1 of the xlr connector (the ground pin) and the copper tape around your piezo disc. You’ll probably have to puncture a small hole in the plasti-dip, but you can always paint another layer of it on later. Also make sure that you are getting continuity to the metal enclosure from pin 1.
Good luck!
-Brach
I took off the plasti-dip, tested both faces of the copper tape and the solder points, as well as the case, the solder on the case connecting to the pcb and both of the ground solder points on the pcb from the xlr ground pin, but couldn’t find any breaks in continuity. Is there anything else it could be or a different way to diagnose the cause?
I assume you’ve tried a different mic cable, correct?
I suggest re-flowing all the joints on the board and xlr cable, even the ground lug on the tin. If it used to work but doesn’t now, most likely a solder joint is cracked on a tiny level that is hard to detect without a microscope.
Alternatively, maybe the sensor disc got cracked or damaged somehow. If you unsolder the sensor cable, do you still get the ground buzz? You’ll most likely get a different type of buzz caused from the input of the circuit being open, but it should sound different. You can test this further by installing a couple of very low value capacitors (anywhere around 100pF or so) between PZ1 and ground, and PZ2 and ground, which emulates the piezo sensor. If you do this, the buzz should go away completely, if the problem is the sensor.-Brach
