so ive been fighting this thing for about three weeks now and i think i finally got it to a point where it actually receives something. its a simple DC receiver for 40m, pretty much the classic NE602 front end into an LM386 audio stage design thats been floating around the internet forever. built it dead bug style on a piece of copper clad.

the good news is i can hear SSB stations on it, which is honestly more than i expected for a first attempt. the bad news is theres this really nasty hum thats just always there in the background and it gets worse when i touch the chassis or move my hand near the board. i added some bypass caps on the power rails which helped a little but didnt kill it. also getting some microphonics, like if i tap the table the audio goes nuts for a second.

anyone dealt with this kind of thing before? i'm running it off a 12v wall wart right now which is probably part of the hum issue, i know i should try a battery but even with battery power i still get the hand capacitance thing going on. wondering if my layout is just bad or if there's something else im missing. the VFO section is a colpitts oscillator and its sitting pretty close to the mixer chip which probably isnt ideal.

the hum almost certainly is your wall wart, those switching supplies are terrible for sensitive receiver front ends. try a 9v battery or a proper linear regulated supply and i bet it drops way down. for the hand capacitance issue thats almost always a shielding problem — your VFO needs to be in its own shielded enclosure, even just a tin can works. the colpitts sitting next to the NE602 is definitely not helping, oscillator leaking straight into the mixer. seen this exact setup before and usually a chunk of copper flashing bent into a little box around the VFO section cleans it right up. the microphonics are a little harder to fix after the fact honestly, partly just the nature of dead bug construction. some people use a little dab of silicone on components that ring but your mileage may vary with that approach.

yeah the wall wart thing is real but also check whether your ground plane is actually continuous — ive had builds where i thought i had a solid ground but there were these little gaps in the copper clad that were basically acting like slots and picking up all kinds of garbage. also how long are your leads on the audio section? the LM386 is notoriously easy to get oscillating if the feedback path isnt kept short. i had one that sounded like a motorboat for like two days before i figured out the output cap lead was running back over the input. anyway congrats on actually getting audio out of it, getting to that point is half the battle with these things.