so ive been working on this direct conversion receiver for 40m for like the past two months on and off, based loosely on the NorCal 40A design but with a few mods i found in an old QST. got it mostly working last weekend and i can actually hear stations which honestly surprised me after all the grief i had with the LO section.

the problem is the audio is just... rough. lots of hum and what sounds like hash, especially when i touch the cabinet or move the coax around. im using a TL072 for the audio amp stage and i wonder if thats the weak point. also my ground plane situation is kind of a mess on the ugly construction board, lots of little islands that probably arent connected as well as they should be.

anyone else fought this kind of thing on a scratch built DC rx? not sure if im chasing a grounding issue or if the audio chip is just picking up everything because the gain is so high at that stage. the LO is a colpitts oscillator running around 7 MHz and i havent shielded it at all yet which might be part of it

yeah grounding on ugly construction can be a real nightmare, i went through the exact same thing on a 20m DC rx i built maybe three years ago. what helped me more than anything was basically treating the whole ground plane as a single star point and running individual ground returns back to one spot instead of just hoping the copper board ties everything together. also if your LO isnt shielded thats almost certainly contributing, even a little tin can soldered around it makes a huge difference, i used an altoids tin once and it worked fine.

the TL072 should be okay for that application, its a bit noisy compared to something like an NE5532 but shouldnt be that bad. id look at your power supply decoupling first honestly, a big electrolytic right at the board plus some 0.1uf caps at each IC and see if that cleans things up before you start tearing into the RF side

touching the cabinet changes the audio? thats almost always a shielding or ground loop thing in my experience. ive had that exact symptom and it drove me nuts for like a week before i figured out i had the audio ground and the RF ground going to different points and they were like 0.3v apart or something. DC receivers are super sensitive to that stuff because of all the audio gain you need.