so i finally got my direct conversion receiver working after about 3 weeks of fiddling with it on the bench. its based loosely on the NE602 design you see everywhere, 40 meters, nothing fancy. i wound my own toroid for the BFO and honestly that was the most frustrating part, kept getting the inductance wrong until i just sat down and counted turns more carefully.

anyway its working, im hearing SSB stations pretty clearly, some noise floor issues i think are just my layout because i built it ugly style on a piece of copper clad and the ground plane situation is kind of a mess. my question is about the audio stage — im running an LM386 after the 602 and there's this persistent hiss that gets worse when i turn up the gain pin. i added the cap between pins 1 and 8 like every schematic shows but its still pretty hissy. is that just the nature of the LM386 or am i doing something wrong with the input impedance matching? i feel like the 602 output into the 386 input might not be ideal but i dont really know what im looking for here.

also the image rejection is pretty bad obviously since its DC but wondering if anyone has added a simple front end filter to one of these and if its worth the effort at this stage or if i should just live with it for now

yeah the LM386 is kind of notorious for that hiss, its a cheap part and it shows. the cap trick helps a bit but youre not going to get a quiet audio stage out of it no matter what you do. a lot of people swap it out for an LM380 or just build a simple discrete class A preamp stage — makes a noticeable difference. also check your bypass caps on the supply, even small amounts of ripple on the rail gets amplified right along with everything else and sounds like hiss.

as for the image rejection, for a first build id honestly just live with it and learn the radio as-is. once you understand what youre hearing you can add a bandpass filter later and youll actually appreciate what it does. putting too many fixes in at once makes it hard to know what actually changed anything.

im in almost the exact same situation, built a 602 based direct conversion for 20m a couple months ago. the hiss drove me crazy too. what helped me was keeping the gain jumper off pins 1 and 8 entirely and just using the 386 in its default low gain config, then adding a separate preamp before it. sounds counterintuitive but the hiss dropped a lot. also make sure you have that 0.047uf cap on the output to ground right at the chip, mine was oscillating at like 400khz and i couldnt figure out why things sounded weird until i put a scope on it