MacMons

Simpler solution, at least for me. What I found was insufficient ground pads on the microphones and R16. This only factors when you move the mics off of the board. Which is exactly what we want in a helmeted costume. So, on the trace side, scrape off some of the green protective layer on the ground plane near the negative posts of each mic and at both ends of R16. Bridge the pins to the scraped off area. If already assembled, just use a bit of wire. But if building a new kit, just strip enough wire to reach and solder the wire to both the original pad and to the scraped clean area. For R16, just bend the leads over to reach the cleaned area and solder to both pad and scraped area before you trim the leads. This gives sufficient ground to eliminate the humming you are hearing. That's all it is, a bad trace design by Velleman that works if you assemble the kit as designed, but not for us helmeted users. I have messaged them about this, but never got a reply. Looking at recent kits, they haven't changed it. But, it's a simple fix. To test this without any soldering, attach a piece of wire to each mic case, holding tight with your fingers. The hum should vanish.