The low-level output of a detector is:

The detector stage in a receiver extracts the original information (baseband or audio signal) from the intermediate frequency (IF) carrier. However, the signal that emerges from the detector is typically very weak and lacks the electrical power to drive a speaker or headphones directly. To make this low-level audio signal usable, it must be routed to an Audio Frequency (AF) amplifier. The AF amplifier boosts the voltage and current of the audio signal to a level sufficient to drive the audio output transducer. Feeding the detector output directly to a speaker would result in audio too faint to hear, applying it to an RF amplifier makes no sense because the signal is no longer at radio frequencies, and grounding it would simply destroy the signal entirely.