so ive been building this direct conversion receiver for 40m based loosely on the Sudden design, swapped out a few parts because i couldnt source the originals and honestly thought it would be close enough. the thing actually receives signals now which is more than i expected after the first smoke test went badly, but the audio is just... rough. lots of hum, kind of a raspy quality to everything, and strong stations sound almost distorted even when im barely touching the volume pot.

the LO is running off a VXO built around a 7.1 MHz crystal i pulled from an old CB radio, not sure if thats part of the problem. the audio amp stage is basically a LM386 with the gain cranked because i thought more was better (i know, i know). power supply is a wall wart 12v switching supply that i had laying around. i built the whole thing ugly style on a piece of copper clad and the layout is probably a mess if im being honest.

anyone been through this kind of thing before? not sure if i should chase the power supply issue first or look at the audio amp stage, or if theres something fundamentally wrong with the mixer i havent thought of yet.

the switching wall wart is almost certainly a big part of your problem, those things dump noise all over the place and a DC receiver is going to pick it up no matter what you do. i had the same exact situation with a 20m regen i built a few years back, drove me crazy for a week before someone told me to just try a battery and see what happened. tried a 9v battery and the hum dropped by like 80% instantly. if you can, throw a 7805 or a proper linear reg in there with some decent filtering caps before anything else.

the LM386 with the gain cap is also worth looking at. the 1.2k between pins 1 and 8 trick to back off the gain a bit helps a lot with that raspy thing you're describing, though honestly if your mixer output is already overdriving the input you might need a voltage divider before the amp anyway. direct conversion receivers are real sensitive to all of this stuff because you dont have a bunch of IF filtering cleaning things up before it hits the audio chain.

CB crystal for the LO is a bit of a gamble on 40m depending on exactly where you land, but shouldnt cause the audio quality thing by itself. id vote power supply first, switching supplies and homebrew analog stuff just dont play nice and its the cheapest thing to rule out. battery test takes 30 seconds.