so anyway ive been building this direct conversion receiver for 40 meters over the past couple months, been using the ugliest ugly construction youve ever seen, just manhattan pads thrown on a piece of copper clad and soldered together wherever things line up. the VFO is a colpitts running around 7 mhz and it locks up pretty decent, drift isnt terrible after warmup maybe 100-200 hz over 20 minutes which i can live with for SSB.

the problem is the audio coming out of the LM386 stage is kind of buzzy and distorted especially on stronger signals. ive got a bypass cap on pin 7 and the usual stuff on pins 1 and 8 to set gain, but something isnt right. also picking up a fair amount of 60hz hum even running off a 9v battery which is weird. the RF frontend is just a simple bandpass filter and a diode ring mixer which i breadboarded first and it worked great but now that its soldered up the audio is just rough.

anyone dealt with LM386 audio issues in homebrew receivers? wondering if its oscillating or if my layout is just causing problems. i can post some pictures of the board if that would help diagnose

the LM386 is kind of notorious for being a little finicky in RF heavy environments, which a receiver chassis definitely is. the usual thing people miss is bypassing the supply pin really aggressively -- like 100uf electrolytic in parallel with a .1uf ceramic right at the chip, and then another cap back closer to your power source. if youre picking up 60hz hum on a battery that actually sounds more like a ground loop or maybe your audio wiring is running too close to the mixer section and acting like an antenna.

also what value did you put on pins 1 and 8 for gain? if you cranked it all the way up to 46db or whatever it is with the 10uf cap the chip gets real unhappy with RF getting in. try dropping the gain and see if the distortion on strong signals clears up, sometimes it is literally just the amp being overdriven by a hot signal off the mixer. DC receivers can push a lot of audio voltage on a strong signal.

yeah post the pictures, always hard to diagnose layout stuff without seeing it. but my first guess with manhattan style builds and audio buzz is ground return paths -- like where is your audio ground actually going relative to your RF ground. ive had builds where i thought i had a solid ground plane but the currents were all looping around in weird ways and making noise.

also is your VFO shielded at all? even a little tin can over it can help keep the LO from getting back into the audio chain. i built something similar last winter and spent about three weekends chasing hum that turned out to be my VFO radiation coupling into the output wiring. drove me nuts.