so ive been at this for about three weekends now and i finally got audio out of my little direct conversion rx build. its based loosely on the NE602 mixer design that gets passed around everywhere, with a simple audio stage after it using an LM386. nothing fancy at all.

the thing actually works which honestly surprised me a little. i can hear SSB stations on 40m when i tune around, but the audio is pretty rough and theres this low frequency hum that i cant seem to shake. ive tried bypassing the power supply pins on both chips with 0.1uf caps and it helped a little but not much. running it off a 9v battery doesnt change the hum so im pretty sure its not coming from my bench supply.

also the opposite sideband rejection is basically nonexistent which i know is a known thing with direct conversion but i was hoping it wouldnt be quite this bad. you can hear both sidebands at the same time and it gets pretty muddy on a busy band. is there anything practical i can do about that without going full phasing network, that seems like a whole other project in itself.

anyway just looking for thoughts from people whove gone down this road before. got a schematic i can post if that helps.

the hum on those LM386 builds drives people crazy, pretty much everyone hits this. first thing id check is your ground layout, if youre on perfboard and the audio ground is sharing a long trace with anything on the RF side you get all kinds of weird coupling. star grounding helps a lot with these. also make sure there's a decent cap from pin 7 on the 386 to ground, like 10uf, that bypass is easy to miss and the chip will oscillate or just be noisy without it.

as for the sideband rejection, yeah direct conversion is what it is. you can do a simple RC phasing network on the audio output to get some improvement but honestly for casual listening most people just live with it or they add a narrow audio filter downstream which helps a little perceptually even if it doesnt actually reject the other sideband. the Weaver method gives you better rejection but youre right that its basically a whole second project. if you want clean DC RX that project the whole phasing approach was a rabbit hole i spent like two months in and it was worth it but not for a first build.

i built almost the same thing last year, NE602 into a 386, and had the hum problem too. for me it turned out to be my audio leads acting like an antenna and picking up 60hz from my monitor sitting nearby. moved the thing to the other side of the desk and it dropped way down. probably not your issue but worth ruling out.

post the schematic if you can, easier to spot something specific that way