There is a technique called Direct Conversion, effectively there is no intermediate frequency, detection is by using a local oscillator at the RF signal frequency feeding into the mixer, and out comes audio.I
There are many SSB radio projects listed in Google. One said it has a gain of 100dB and its audio amp is so sensitive that it picks up buzzing from nearby mains wiring.
This only works with SSB and CW.
It has the advantage of being relatively simple, but the downside is that you get a lot of "image" responses, and, you need a LOT of audio gain, which can be a real pain.
JimB