FiiO's K1 USB digital converter has been buried under a pile of crap on my desk for months, but it's not my fault. The K1 is so darned small it's easy to lose track of, but now that I've gotten around to listening to it I'm here to spread the news: this super-affordable gizmo is really pretty decent. You can get the FiiO K1 on Amazon for $40, or £36 in the UK, with free shipping for Prime customers.
The little 2 by 0.3 by 0.8-inch device looks like a thumb drive, with a 3.5mm headphone jack on one end and a Micro-USB port on the other. The K1 needs no batteries, running on power from your computer. A tiny blue LED lights up when the K1 is plugged in.
The digital converter handles high-res files up to 96 kHz/24 bit, and FiiO claims the headphone amp will happily drive 16 to 100 ohm headphones.
The K1 is designed to be used with computers, but some folks claim it works with smartphones. That's a hit or miss proposition; I used the K1 with my Mac Mini and it worked like a charm.
To get started I plugged in my Grado SR 325e headphones, and the K1's sure-footed bass and wide-open stereo imaging on Bob Marley's "In Dub Volume 2" album was definitely up to snuff. Moving onto Dick Hyman's "From the Age of Swing" audiophile jazz album, the K1's clarity and neutral midrange tonal balance came to the fore.
At this point I removed the K1 and plugged the headphone directly into the Mac Mini and the sound thinned out, treble grew coarser, and soft-to-loud dynamics shrank, so the SR 325e sounded like a cheaper headphone. Returning to the K1 restored my faith in the headphone's sound quality!
Next up, I popped on my Hifiman RE600S in-ear headphones, and listened to Amon Tobin's brilliant "Bricolage" electronica album. I was taken aback by how much ultra-deep bass I was hearing. Not only was it deep, but bass definition and detailing were above and beyond what you might expect from a budget headphone amp. This headphone is noted for its transparency, and the K1 let it shine.
The K1 isn't just for headphones -- you can also use it with powered speakers, like my desktop Adam Audio F5s. Again I had no complaints, the sound was quite decent. So if you're looking to upgrade your computer's sound for not a lot of money, the FiiO K1 would be a wise investment.