Like a lot of people I use my mobile device as an audio source in my car. Unfortunately, like a lot of people if I plug my mobile device directly into the aux input on my car volume levels are extremely low. I have a choice, either crank up the volume on my head unit to the max and experience a hefty amount of distortion, or listen at low volume levels. A third, and much better sounding option is to boost the audio signal prior to sending it to the AUX input, or pre-amplify the signal. Lucid Labs CMOY portable headphone amplifiers are perfect for this application, simply plug a 3.5mm stereo audio cable from your mobile device into the amplifier's input jack and then plug another 3.5mm stereo cable from the amplifier's output into the AUX input and turn on the amp.
