so anyway i've been slowly building this direct conversion receiver for 40m over the past few months, nothing fancy just the classic NE602 mixer into an LM386 audio stage with a low pass filter in between. got it oscillating on frequency which took way longer than it should have honestly, my junkbox variable cap is a bit sketchy and the tuning is super touchy near the band edges.

problem is the audio sounds kind of phasey or hollow i guess? hard to describe. SSB signals are intelligible but they have this weird quality like listening through a tin can. CW is actually fine and sounds clean which is confusing me. i double checked my decoupling caps on the 386 and they look okay, and the supply voltage is stable at 9v. wondering if maybe my IF filter is doing something weird or if theres some kind of feedback path i'm not seeing. layout is pretty loose on a piece of copper clad which probably isnt helping

anyone dealt with this before with the 602 designs? ive built a regen before but this is my first proper superhet attempt, or well i guess DC receivers arent really superhets but you know what i mean

that hollow phasey sound on SSB is almost certainly audio feedback or RF getting into the audio stage. the LM386 is notoriously easy to get oscillating or picking up garbage if the layout isnt tight. the classic fix is a 10 ohm resistor in series with pin 7 (the bypass pin) and a 0.047uf cap to ground, plus make sure you have a cap right at the supply pins of both chips, like physically right there not somewhere else on the board.

also with direct conversion receivers you get both sidebands at once so SSB can sound a bit weird by nature, you kind of have to tune to one side of zero beat to minimize the other sideband. might not be a fault at all just the nature of the beast. CW sounding fine makes sense because both sidebands just give you a tone anyway so it adds rather than interferes.

I built almost this exact thing a while back from the ARRL handbook design and had similar issues. For me it turned out the ground plane on my ugly construction had a gap right between the mixer and audio sections and I was getting a ground loop kind of situation. just bridging it with a bit of braid fixed most of it. also my NE602 was running a bit warm which i read somewhere can cause stability issues but im not sure if thats actually true or i just imagined it fixed itself lol