What exactly is a digital amp?

THE PRICE!!

I believe they perform the signal amplification in the digital domain, with the signal being broken down into 0's and 1's. They have a much higher sampling rate than redbook CDs and some offer analog and digital inputs. The power supplies appear more efficient than those found in analog designs. They are lighter, run cooler, and are generally less noisey than their analog counterparts.

I recently bought Panasonic's SA-XR45 digital, 6-channel receiver, which can be found for around $300 on the Internet. I must admit that overall I prefer it to some highly-rated tube and solid-state analog amps I've had in the same system with my Klipsch Chorus. I see a very strong case for digital amps in the future.

I still use tube-MOSFET hybrid monoblock amps in my main reference system, but in the future I may try digital amplification based on my positive experience with the Klipsch/Panasonic system. BTW, Newform Research recommends the Panasonic XR-45 for bi-amping their R645 speakers (used in conjunction with a Behringer digital crossover)...

So when Theo says, "THE PRICE!!!", I'm not sure which way he means it!!! Some digital amps (TACT, for example) are expensive, but the technology is rapidly trickling down...

The digital amp has an output stage working on constant switching from 0 to 1. For every 0 and 1 there's a specified output voltage and current. The signal is primerely being broken by the clocking circuitry that defines the switching ratio of an output stage.
The higher the clocking freequency is the higher precision and clarity of a digital amp you'll get.
The main benefit of digital amp that it's always on the stand-by mode and "waiting" for the command of cloaking circuitry thus being not affected by heat dissipation losses and very efficient energy consumer.

TACT, PS Audio, Acoustic Reality, Spectron, Bel Canto, and maybe the Sunfire, are all examples of digital switching amps. Class D and Class T are Digital Amps.I don't know for sure about Class H amps.Class H amps are switching amps, but I don't know for sure if they would be classified as digital amps or not?
They are very efficient and run cool.Some don't even have heat-sinks at all! I have never heard one, but have read rave reviews on some of them, and heard good word-of-mouth on them.