so I finally finished winding all those toroids and got my 40m direct conversion receiver together based loosely on the Sudden receiver design, been meaning to do this for like two years and just kept putting it off. anyway it actually picks up signals which honestly surprised me a little because my soldering on the audio stage looked pretty rough.

my issue is there's this pretty noticeable hum on everything, like 60hz I assume, and I'm not sure if it's the power supply (just using a wall wart right now), the audio amp section, or maybe a grounding thing. I did most of the construction on a piece of copper clad with ugly style and the ground connections all seem solid when I check them but who knows.

also the audio is a bit muffled, wondering if maybe my low pass filter values are off or if the NE5534 stage needs some tweaking. reception seems decent on SSB but CW is where it really shines which makes sense. anyone been down this road with a DC receiver and hum issues specifically?

the hum is almost certainly your wall wart, those switching supplies are terrible for this kind of thing. i went through the exact same thing with a similar build and swapped to a proper linear regulated supply and it cleaned up like 90% of the noise. even just a 7812 or 7809 depending on your voltage requirements with some decent filter caps before it will make a huge difference. also check that your audio ground and your RF ground are tied together at one single point, if you have a ground loop anywhere in that audio chain it will hum like crazy no matter what supply you use.

the muffled audio could just be the passband on your LPF, what values did you end up using for the cutoff? for SSB you want to think about rolling off around 3kHz or so but if you went too conservative it'll sound like everyone is talking through a pillow.

yeah DC receivers and hum are basically old friends at this point lol. one thing people dont always think about is the VFO bleedthrough into the audio path, depending on how close your oscillator is physically to the audio amp you can get some weird coupling that shows up as noise or instability. shielding the VFO section with a small tin can or even some copper tape can help a lot.

nice work getting it on the air though, the Sudden design is a good starting point. I built something similar years ago and it got me hooked on homebrewing. eventually went down the rabbit hole of building a full transceiver from scratch which took about three years but thats another story