so anyway i've been building this superhet receiver for like 3 months now, mostly on weekends when i have time, and i finally got audio out of it last night which was exciting but the IF stage is doing something i dont really understand. im using a 455kHz ceramic filter i pulled from an old AM radio and the selectivity seems way too broad, like i can tune across a whole shortwave station without it really cutting off at the edges. the BFO is working fine i think, i can hear SSB signals okay but they kind of blend into adjacent signals more than i'd expect.

the circuit is pretty basic, standard NE602 mixer feeding into a couple stages of IF amp built around some LM386 chips i had laying around, then the ceramic filter right before the detector. i'm wondering if i have the filter in the wrong place or if 455kHz ceramic filters from AM radios just aren't designed for SSB use. read some stuff online that was kind of contradictory. also my AGC isn't hooked up yet so strong stations are just crushing everything which probably doesn't help.

anyone built something similar and run into this? i'm not sure if this is a filter placement problem or just the nature of cheap ceramic filters or what. could also be my IF transformers are peaked at the wrong frequency, i just set them with a screwdriver until the noise seemed loudest which probably isn't the right way to do it

yeah that ceramic filter is almost certainly your problem, at least for SSB. the ones pulled from AM radios are typically like 6-8kHz wide at -6dB, sometimes wider, which is fine for AM broadcast but way too broad for SSB where you want something more like 2.4kHz or so. you can sometimes find narrower 455kHz filters marketed as SSB or CW filters, Murata and TDK made some decent ones, but honestly pulling one from a random AM radio is kind of a crapshoot. also worth noting that LM386 is kind of a pain in the IF stage, it's really meant to be an audio amp and it can be a bit noisy and prone to oscillation when you try to run it at IF frequencies with any real gain. NE602 into a proper IF transformer chain would probably serve you better there. the peaking by ear method works in a pinch but you really want to peak those IF cans for maximum signal output on a known frequency, not just noise, otherwise you might be peaked off-center and that'll definitely hurt your selectivity.

i built a similar thing a while back and had almost the exact same issue. what worked for me was just ordering a proper 455kHz SSB filter, i think mine was a Murata SFU455 or something close to that, cost like a couple bucks on ebay. made a huge difference honestly. the AGC thing is real too, running without it you'll just get stomped by anything strong and it makes everything sound worse than it actually is. i ran mine without AGC for a while thinking i'd get to it later and it really does mess with your perception of how the receiver is actually performing.