so i've been putting this thing off for like two years, always buying kits or used gear but never actually building from scratch. finally sat down over the past few weekends and put together a direct conversion receiver for 40m based loosely on the Sudden receiver design, but i swapped out a few parts because i couldnt source the exact ones listed and figured close enough would be fine.

the VFO is a colpitts oscillator running around 7 MHz, driving a NE602 as the mixer, then into a pretty basic audio chain with an LM386 at the end. i was fully prepared for it to not work at all on first powerup but i'm actually hearing SSB signals on it. not perfectly, there's a fair bit of hum and the audio is a little muddy, but actual signals are coming through and i can tune across the band and hear different stations.

my question is the hum — i'm running it off a wall wart right now and i suspect that's at least part of the problem. would a proper regulated supply help a lot here or should i be looking at decoupling on the board first? the layout is pretty rough, just point to point on a piece of veroboard.

congrats on getting it going, that's the hardest part honestly. the hum is almost certainly a combination of both things you mentioned. wall warts are pretty noisy and the LM386 is notorious for picking up every bit of supply noise if you dont decouple it properly. the classic fix is a 250uF cap from pin 7 to ground and make sure you've got a 0.047uF from the output to ground through a 10 ohm resistor or it'll oscillate like crazy. also check if you have any decoupling right at the NE602 supply pin, that thing is surprisingly sensitive to supply noise too. a 100uF electrolytic in parallel with a 0.1uF ceramic right at the chip goes a long way. try a 9v battery as a quick test, if the hum drops significantly then yeah its your supply and you can sort that out properly rather than chasing ghosts on the board.

the veroboard layout can cause you a lot of grief too, ground loops and stuff. i built something similar a while back and spent ages chasing hum before i realized i had the audio ground return running all the way back across the board through like three other sections. star grounding made a big difference. anyway good on you for actually building it, most people just talk about it