so i finally got my direct conversion receiver working on 40m after about three weeks of head scratching and i'm pretty stoked about it. its based loosely on the NorCal 40 design but i kind of went off script with the audio section because i had some LM386s laying around and figured why not. reception is actually decent, picked up a bunch of SSB traffic last night no problem.

my issue is theres a pretty noticeable hum on the audio, like 60hz kind of hum that gets worse when i touch certain parts of the board. i double checked my ground plane and it seems okay but im wondering if its a power supply thing. im running it off a wall wart right now, one of those old switching ones i had in the junk box. would a linear supply clean that up or is there something else i should be looking at first. also the LM386 runs warm, like not burn your finger hot but warmer than i expected - is that normal for those chips

yeah that hum is almost certainly your switching supply, those things are noisy as heck and the LM386 will pick it up no problem especially in a DC receiver where you dont have a lot of selectivity to knock garbage down before the audio stage. swap in some batteries for a test first before you go buying anything - if the hum disappears you have your answer. linear supply would definitely help but even just a good LC filter on the supply rail can do a lot if you want to stick with the wall wart. a 100uH choke and a couple hundred uF caps in a pi filter usually cleans things up pretty well.

the LM386 warmth is pretty normal honestly, its a hungry little chip and depending on your gain setting and supply voltage it can dissipate a fair amount. what voltage are you running it at and what do you have on pin 1 and 8 - if you've got the gain cranked all the way up thats part of it too

congrats on getting it going. those direct conversion rigs are a real rabbit hole once you get the bug, ive built probably four or five variations over the years and still learning stuff. the hum thing - definitely try batteries like the other guy said, that's the quickest sanity check. i had a similar issue on one of mine and it turned out to be a ground loop between the audio board and the main board because i had them connected at two different points. ended up just running a single fat ground wire from one central point and it cleared right up.