Korg HA-S Nutube Headphone Amplifier DIY Kit HAS B&H Photo Video
Headphone Amplifier Donner 4 Channels Metal Stereo Audio Amplifier,Mini Earphone Splitter with Power Adapter-4x Quarter Inch Balanced TRS Headphones Output and TRS Audio Input for Sound Mixer-DEL-4 - Walmart.com
Basic Headphone Amplifier Kit An Analog Educational Kit About Op Amp Applications