sackley: TIM is transient intermodulation, another kind of distortion spec that describes how clean the signal runs through the zero line (ground level). It has something to do with the linearity of a transitor's amplification - that's where class A operation comes into play: If you add some additional - uhm... what's the English equivalent for Ruhestrom?
- constant current, you lift the transistor into the linear part of its amplification curve, but thereby you sacrifice quite a lot of power. Some amps can be switched from regular class B into class A operation - the Marantz PM8000 for example. This can be helpful, if you want to use your amp for both personal Hi-Fi use and as PA-workhorse for parties....
Nevertheless, it's yet another spec: If you don't exactly know how each manufacturer measures, it will only serve as a hint - quite similar to S/N-ratio, THD, wattage... Nowadays even cheap amps have very good specs (on paper, at least), so the specs won't tell you a lot, anymore. Usually I find it more revealing to have a look inside the amp, because the types and dimensions of parts as well as the board layout and cabling can tell you quite a lot if you have a little experience. So better trust your ears - and maybe your eyes, too.
Greetings from Munich!
Manfred / lini