High Resolution Technologies (HRT) has a reputation of making great value USB DAC, with all products designed and manufactured in California USA. HRT microStreamer is the breakout product that cements that impression with great reviews and multiple awards.
HRT microStreamer is tiny measures just 1 x 3 x 6 cm, and connects to your computer via USB. It has two outputs, one for your headphones and the other for connecting to an amplifier or powered speakers. It uses asynchronous USB for a jitter free audio, and is capable of up to 24bit 96kHz.
HRT microStreamer is one of the few portable DAC that is compatible with iOS devices with no additional power required. To use with your iPhone or iPad, you need Apple’s USB Camera Adapter and iOS 7.