How you set up a microphone to play through your audio receiver's speakers depends on the kind of equipment you have or are willing to buy or rent. Most receivers are capable of directly connecting to microphones, but this often doesn't produce optimal performance. Typically, you need some extra equipment to get the best performance from your microphone and receiver.
Most audio and AV receivers feature a dedicated microphone jack, often marked Line-In, Mic or AUX. The simplest and usually least expensive option is to directly connect your microphone to this jack and switch to its input channel. However, with most microphones you'll find that there is a significant drop in volume compared to your other devices.
The reason for this drop in volume is that microphone lines carry audio at a substantially lower decibel level than other audio devices. Since the microphone can't supply the same level of volume to the receiver, a direct connection means you have to turn the volume up considerably in order to be heard clearly.
Preamps and Sound Mixers
Preamplifiers and mixers are a good way to mitigate the volume loss that occurs by connecting your microphone to your receiver. Preamps increase the signal strength of connected devices like a microphone to the same line level as other audio devices. Sound mixers can be used to adjust the signal and volume of connected audio devices such as a microphone. These devices act as an intermediary between your receiver and your microphone. Using a preamp or mixer, you can increase the volume level on the microphone without having to dramatically increase volume on your receiver.
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Typically, when hooking a preamp or mixer to your audio receiver, connect the microphone to the Line-In or Mic jack on the device, then connect the device to the receiver's Line-In or Mic jack. Set-up instructions may vary from one device to the next, so check the owner's documentation for your preamp or sound mixer.
If your intent is to blend microphone input with music for singing, investing in a karaoke machine may be a good choice. Karaoke machines generally come in two configurations: Stand-alone devices that include their own screen and speakers, and machines that connect to your TV and speakers. Karaoke machines are specifically designed to amplify microphone input and mix the microphone channel with music, and many feature input jacks for at least two microphones.
In most cases, setting up your karaoke machine means connecting it to your receiver's Line-In or Audio-In and Video-In jacks, depending on the type of karaoke machine you're using. Check with your karaoke machine's owner's documentation for setup instructions specific to your device.