so ive been slowly putting together a direct conversion receiver over the past few weeks, nothing fancy just a NE602 front end with an audio amp stage tacked on, wound my own toroid for the bandpass filter which honestly took longer than everything else combined because i kept losing count of the turns. anyway plugged it in tonight expecting the usual wall of hiss and static and i actually heard someone on 40m calling CQ, couldnt believe it. signal wasnt great and theres a weird hum i need to track down, probably my power supply since im just running it off a wall wart i found in a drawer. but still, it works. or at least it does something that resembles working.

the audio is a little muddy and i think the BFO isnt quite right because SSB sounds like everyone is talking through a kazoo but CW comes through pretty clean actually. i breadboarded the whole thing which is probably why the hum is so bad, ground loops everywhere im sure. gonna try to get it into a real enclosure once i figure out what im doing wrong with the demodulation side. anyone else built around the NE602 and have tips for getting the audio stage cleaner? ive seen a bunch of designs use an LM386 but i read somewhere that chip is kind of notorious for oscillating if you sneeze near it

yeah the LM386 is a pain, its almost a rite of passage dealing with that thing. the trick that finally worked for me was the bypass cap on pin 7, like a 10uF to ground, and keeping the gain jumper at minimum (pins 1 and 8 open) until you actually need more volume. also putting ferrite beads on the power leads helped a lot. that said if you're still on breadboard you're going to fight hum no matter what, RF and sloppy layouts dont get along.

the BFO offset thing on the 602 is just tuning, you want to be somewhere around 700-800hz off the carrier frequency to get SSB sounding decent, fiddle with your VFO until voices stop sounding like donald duck. its all a bit of a fuss but once you get it dialed in its pretty satisfying. what frequency is your local osc running at?

nice work getting it going, first time you hear an actual signal on something you built yourself is kind of a weird moment. i built one of those 40m DC receivers from a magazine article a while back and the hum drove me absolutely crazy for like two weeks before i realized my bench supply was the whole problem, swapped to a proper regulated supply and it was night and day. wall warts are pretty variable on how clean they are.