so ive been puttering around with this DC receiver for about three months now, kept setting it aside when work got busy but finally had a weekend to just sit down and get serious about it. its based loosely on the Norcal design but i swapped out some of the filter caps and used what i had in the junk box which was probably my first mistake honestly

anyway it receives, like actually receives signals, i can hear 40m SSB pretty clearly which was shocking. the problem is theres this weird hum that follows the audio everywhere, not 60hz exactly but close, and i cant figure out if its the power supply coupling in somehow or if its a grounding issue with the audio stage. ive got a single point ground on the board but maybe i did it wrong. also the image rejection is pretty bad but i knew that going in with a direct conversion design so im not too worried about that part

has anyone dealt with this kind of hum specifically in homebrew DC receivers? i wrapped the whole thing in copper tape on the inside of the enclosure and it helped maybe 20% but its still there. using a 12v wall wart right now, maybe thats the issue, should i just slap a 7812 regulator and some filter caps on it before the board

yeah the wall wart is almost certainly your problem, or at least a big chunk of it. those switching supplies are noisy as heck and even with filtering they can get into the audio stage. i had the exact same issue on a regen i built a few years back and just dropping in a linear regulated supply made like 80% of the hum go away overnight. a 7812 with a good 2200uf cap on each side and maybe a small .1uf ceramic right at the board power pins should clean it up a lot

also worth checking if the hum changes at all when you touch the enclosure or move the audio cable around. if it does youve got a grounding loop somewhere in the signal path. the copper tape thing helps for RF shielding but it doesnt do much for audio frequency noise unless its actually connected to your circuit ground properly at one point

direct conversion receivers and hum are basically old friends lol. one thing people dont always think about is the orientation of any transformers you have near the audio stage, even small ones. also what op amp or audio IC are you using in the AF section? some of them are way more sensitive to supply noise than others and just throwing a small bypass cap right at the V+ pin of the chip can make a surprising difference. like right at the pin, not just on the board somewhere nearby.

the image rejection thing btw if it starts bothering you later, look into a phasing receiver variant, way more work to build and align but you can get pretty decent image null with patience. anyway sounds like you're making good progress for a first DC build, these things always have some gremlins the first time around