so ive been building this direct conversion receiver for 40 meters based loosely on the old Neophyte design but i swapped out a few parts because i couldnt source the originals and honestly i thought i knew what i was doing. it receives fine, i can hear stations no problem, but theres this low hum in the audio that follows the signal — like it gets louder when im tuned to a strong station and quieter on a dead frequency. at first i thought it was just 60hz from the power supply so i threw a bigger filter cap on the rail but that didnt really do anything.

the audio stage is built around an lm386 which i know everybody has opinions about but i had a handful of them and its what i used. i wonder if its picking up something through the gain pins, ive heard those chips can be finicky. or maybe its something with my VFO leaking back somehow? i dunno. the whole thing is built on a piece of copper clad with ugly style construction, no enclosure yet because i wanted to get it working first. maybe thats the issue, just picking up everything with no shielding.

anyone dealt with this before? im not sure if its a grounding thing or the chip or what. kind of at a loss here.

the lm386 with no bypass on pins 1 and 8 will absolutely do that — even if youre not trying to use the extra gain it still picks up garbage on those pins. slap a 10uf cap across them and see if it changes anything. also yeah the no enclosure thing is probably not helping, ive had open builds on copper clad that were basically antennas for every switching supply in the room.

the hum tracking with signal strength is interesting though. that sounds less like a power supply issue and more like youre getting audio rectification somewhere, maybe in the detector stage itself. whats your product detector look like, are you using a diode ring or a Gilbert cell or just a single balanced thing? if the detector isnt well balanced you can get AM breakthrough and that can look exactly like what youre describing — louder signal means more detected carrier hum. worth checking your diode matching if thats the route you went.

yeah i had almost the exact same thing happen on a 80m receiver i built a while back. drove me crazy for like two weeks. turned out one of my ground connections on the ugly style build had a cold solder joint and i basically had a ground loop going through the audio section. reflowed everything with fresh solder and the hum dropped way down. not saying thats your problem but its worth going over every joint especially the ground connections to your copper clad sheet.