Electret Microphone Amplifier - MAX9814 with Auto Gain Control : ID 1713 : $7.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Dynamic and Electret Condenser Microphone Preamp Circuit
Amazon.com: S278 15W Lightweight Portable Rechargeable Mini Voice Amplifier with Headset Microphone Supports Bluetooth/Recording/FM Radio/MP3 for Teachers, Tour Guides and More : Musical Instruments
Microphone - Wikipedia
TL072 based Electret mic pre-amp not working correctly... Tinny and quiet. | diyAudio
Shure SM7B microphone review: A great studio upgrade | Popular Science