Amplifiers generally only need servicing if they have audible faults, I wouldn't bother otherwise. Most only need a squirt or two of switch cleaner to stop crackling and intermittent switches and pots. All amplifiers sound very similar, buy one with the highest power output that has the features you need at the price. Auditioning them is a waste of time, so is reading What Hifi reviews.
Some thoughts on this:
- Within amplifiers of the same technology and class, well-designed amplifiers will sound very very similar. One well-done class AB amplifier sounds pretty similar to the next, assuming they're both operating within their limits. At the extremes of performance (driving speakers that dip below 2ohm, for example), the "better" amps will typically have the extra current capability, regulated supplies, etc that would be needed to make sure the sound stays good.
- Once you start comparing amplifiers of different classes, differences can be more apparent. For instance, some class D amps have a high-frequency response that varies (usually only a dB or two at 20kHz) according to the impedance at the terminals. This is because the feedback point is before the output filter, so the LC network isn't accounted for. It's rarely a big problem, and most class D amps include the LC network in the feedback loop.
Class AB amps don't have this issue.
Class A amps don't have the crossover distortion that class AB amps have. You get the idea.
- When you compare the differences between valve amps and transistor amps, there's an even bigger difference. Valve amps can vary wildly in their topology and execution, ranging from push-pull pentodes which are capable of large power outputs and have a sound that starts to resemble that of transistor amps, over to single-ended triodes which are known for the soft/warm/glowy valve sound, low power output, and very soft clipping. There are other valve amps, too, including OTLs which do away with the output transformer and have the valves drive the speakers direct.
Saying that ALL amps sound the same is patently false. It's more correct to say that all similar amps sound the same as long as nobody has screwed up badly.
In conclusion, I'm not that bothered by amplifiers. I want something clean, enough power, and with the right I/O. A midrange class AB amp from a decent manufacturer will be just fine. The super-cheap stuff sometimes works well, but the more expensive ones can typically deliver more current and add other features I'm interested in like a USB input to connect to my laptop.
FWIW, I've used good class D amps for HiFi and also found them to be excellent.
Chris
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