How is Mid Fi defined?

has no tubes.

Mid-Fi is anything anyone can buy at a Big Box store. Same product sold by a boutique store automatically becomes Hi- Fi. :-)

"Components primarily designed to meet the needs of audiophiles and music-lovers are worthy of the appellation "high-end," no matter what they cost. The much wider range of products whose genesis lies purely in the need of their manufacturer to fill a gap in their product line or attack a previously unoccupied niche in the market, or even just to flesh out their business plan, are "mid-fi" by definition. It's as simple as that. The next time you find someone equating the words "high" and "end" with "high-priced," or feeling that low-priced is automatically equivalent to "mid-fi," remind them that it ain't necessarily so."

Source: http://www.stereophile.com/asweseeit/1194awsi2/