so ive been wanting to build a DC receiver for ages and finally sat down and did it over the last few weeks. based loosely on the NorCal design but i changed out a few things because i couldnt source the original parts easily. using a NE602 for the mixer/oscillator and an LM386 for the audio amp stage, pretty standard stuff.

it actually works which honestly surprised me a little. picking up SSB stations on 40m no problem, audio is decent through some computer speakers i had lying around. the VFO is drifting a bit which i expected but its worse than i thought itd be - like if i tune to a station and walk away for 10 minutes the pitch has shifted noticeably. i used a plain LC oscillator with whatever coil i wound on a t50-2 toroid. maybe thats the issue or maybe its just temperature in my shack, hard to say.

also getting some hum that i think is coming from my power supply. its a wall wart 12v regulated one but maybe not regulated well enough? or could be a grounding thing. the hum goes away if i touch the antenna connector which is weird to me.

anyway proud of myself for getting this far but curious if anyone has tackled these same issues on a similar build

the hum going away when you touch the antenna connector is almost certainly a ground loop or floating ground situation. your wall wart probably has the secondary floating relative to mains ground, and your body is providing a reference path when you touch it. try running a wire from the chassis ground of the receiver to a known earth ground and see if that clears it up. also double check your audio ground path, LM386 builds can be real sensitive to layout - if your ground traces are looping around anywhere near the audio section youll pick up all kinds of garbage.

on the drift, t50-2 mixes are decent but temperature coefficient on those cores isnt great for a free-running VFO. the classic trick is to put a small NP0/C0G cap in series or parallel with the tuning cap to temperature compensate. takes some fiddling but you can get it pretty stable. or honestly just buffer the oscillator better so the load doesnt pull it around - even just a JFET source follower between the osc and mixer input helps a lot.

congrats on getting it going, that feeling when you first hear a real signal on something you built yourself is pretty great. i built something similar a while back and the drift drove me absolutely nuts. ended up just putting the whole oscillator section in a small metal box with some foam insulation around it just to slow down the thermal swings, wasnt a real fix but made it manageable. eventually replaced the LC with a DDS module which kind of felt like cheating but hey it works.

the NE602 is a nice little chip but watch your signal levels going in - they clip pretty easy and it sounds awful when they do. if youre in an area with strong local AM broadcast stations those can also sneak in and cause all kinds of weirdness with a simple frontend like that.