They use different technologies and have a lot of technical specs. This enables your amplifier to be stacked on top of your other audio equipment. The vast majority of todays audio amplifiers are solid state amplifiers vs more traditional tube amplifiers. Tube mini amplifiers have been prevalent a decade or so ago. Tube amplifiers, on the other hand, have a rather large amount of harmonic distortion. Harmonic distortion refers to how much the audio signal is degraded whilst being amplified. A few of the most popular technologies in the past have been “Class-A” and “Class-AB” technologies. Amplifiers based on any of these technologies are also referred to as “analog amplifiers”. Whereas amplifiers using these technologies normally have low audio distortion, power efficiency is merely 10% to 30%. “Class-D” amplifiers, on the other hand, which are also named “digital amplifiers” have a power efficiency of at the least 80% and are smaller and have a smaller power supply than comparable analog amplifiers. The downside is that many digital amps have higher audio distortion than analog amplifiers although several of the most recent models employ a feedback mechanism to minimize distortion to levels of 0.05% and below. The required power will be determined by how much power your loudspeakers can tolerate as well as the size of your space where you will be listening. You would almost certainly be good getting an amplifier that can offer 20 to 50 Watts although your speakers might be able to tolerate 100 Watts of power.