so i finally finished winding all the toroids and got my direct conversion receiver for 40m up and running last weekend. been wanting to build one of these for years honestly. used the NE602 as the mixer/oscillator and an LM386 for the audio amp, pretty standard stuff i know, but figured id start simple before getting into anything more complicated.

thing actually works, which surprised me a little if im being honest. i can hear stations, SSB sounds passable, CW is pretty clean. but theres this weird audio artifact - hard to describe but it almost sounds like a low frequency hum underneath everything, not 60hz exactly, maybe more like 120hz? and it gets worse when i touch the enclosure or even just move my hand near the board. i havent shielded anything yet, which is probably dumb, and the power supply is just a wall wart i had lying around so thats probably part of the problem.

wondering if anyone else has dealt with this with the LM386 specifically. ive read that thing is kind of a noise magnet if you dont bypass it properly. i have a 10uf on the supply pin but maybe that's not enough? the layout is also pretty much just point-to-point on a chunk of copper clad with no ground plane to speak of, just lots of little ground wires everywhere.

yeah the LM386 is notorious for picking up garbage if you look at it wrong. 120hz is almost certainly your wall wart - those cheap switching ones are brutal for anything RF or audio sensitive. try running it off a 9v battery and see if the hum goes away, if it does then you know where to start. also that bypass cap on pin 6, 10uf is fine but you really want a 0.1uf ceramic right next to it too, like physically as close as you can get it to the pin. the combination of both usually cleans things up a lot. and yeah, shield it. even just folding some copper clad around the audio section helped mine considerably. the NE602 stage probably doesnt care as much but the audio board will pick up everything.

i built basically the same thing a couple years ago, almost identical parts. the touching the enclosure thing you mentioned - is it getting louder or quieter when you touch it? because if its quieter that tells you something different than if its worse. mine was picking up hum through ground loops between the two stages, ended up having to run a single point ground back to the power entry rather than just daisy chaining everything together. took me forever to figure out. also dont underestimate how much better it gets once you get it in a real metal box, even just a diecast aluminum one from hammond or whatever. point to point on open copper clad is a great way to prototype but it'll pick up every bit of RF and hum in the room.