I think the very best amplifiers are like wire with gain. That is, they add or take away nothing from the sound quality. They just boast the signal enough to drive the speakers. An amplifier that does this requires the source and speakers to be well matched. Often times, people will choice an amplifier that will “color” the sound to componsate for their speakers characteristics. For example, speakers which are known to be “bright” are often paired with a tube amplifier.

One of the first question with amplification is whether you are going to use an integrated amplifier or separate components. The advantage with integrated amplifiers are they they tend to be less expensive and offer more value than equivalent separates. If you are spending less that $3000 on a system and don’t plan on playing the upgrade game, you should strongly consider using an integrated amplifier. The advantage of separates is that you have more flexibility and are able to update one piece at as time.

If you aren’t familiar with electronic design, you might want to read the wikipedia article about electronic amplifiers. Most high quality pre-amps use a class A circuit design. Most power amplifiers are class A/B, the better ones are designed to be pure class A through normal listening levels and switch to class B when there is a need for a lot of power. Most companies don’t make class A amplifiers because they are less efficient (run hotter, use more electricity) and will be more expensive to build than an A/B amplifier of similar output power. On the other hand, it’s easier to design a clean class A amplifier. Most class A integrated or power amplifiers are expensive. It is possible to build low to moderate class A power amplifiers (say less than 20 watts) which are reasonably priced.

The wikipedia article mentioned that there is something called a class D amplifiers. Class D amplifiers are more efficient than class A or A/B amplifiers. Until recently nearly all class D amplifiers were designed for efficiency and not for high fidelity. In recent years a number of decent class D amplifiers have hit the market. I predict that as more people figure out how to build high quality class D amplifiers, that we will see class A/B largely disappear from the mass market. Why?  The class D amplifiers don’t sound as good, but they are close enough while being cheaper, more compact and more power efficient. Welcome to the iPod generation where people don’t seem to care as much as audio fidelity. I expect that class A and A/B will only be found audiophile orient products in ten years.

Now back (mostly) to conventional A and A/B designs. Amplifiers that I like

• Exposure 2010S, – simple, minimal features, but you would have to spend at least twice this much to get as well rounded and good sounding amplifier.
• Peachtree Integrated Amplifier. Lots of features, well though out. I think of this as the modern NAD 3020… a really good starter system.
• Bluecircle I have heard good things about their integrated amps, but not listened to it myself.

For less performant / expensive options I would suggest looking at  Rotel and NAD.  I would also recommend look at the used market. My favorite older amplifiers are the Classe’ CAP 80/100, Bryston B-60 SST (slightly updated Bryston B-60 is still made but overpriced), YBA Integre, Acurus DIA-100, and Krell KAV 300 (updated as the 400 and overpriced). Each of these integrated amps with extremely well built and provides extremely good sound quality. You could also look for one of the  for one of the The Ten Most Significant Amplifiers of All Time as selected by the TAS staff.

It used to be that there were four good choices for moderately priced seperates at the high end of consumer electronics, or low end of audiophole: Rotel, Parasound with NAD and Adcom trailing slightly behind. Adcom seems to be history now. A newer company getting very good reviews is Emotiva. Their combination of some good designs, Chinese manufacturing, and direct marketing has produced some excellent products for the money. Several of the engineers at Martin Logan recommend them as a modestly priced amplfier.

I was surprised how much of a difference the preamp can make. I found a great deal of difference between comparably priced preamps when doing blind A-B testing. I did not find that similarly priced power amplifiers varied as much as the preamps did. Ultimately, I discovered that the superior pre-amps where all discrete components using class A amplifier circuits. In recent years I have experimented with not using a pre-amp. Since my music is coming from a single source I have wondered if simplifying the signal path could result in better source. Not surprisingly, the answer depends on the source. In most cases, I found a good preamp significantly improved the sound quality when placed between a source and a power amplifier. One notable exception was the Lavry Black DA11 DAC. I found that I couldn’t tell the difference between the Lavry driving my power amplifier directly, or passing through a high quality pre-amp.

Most of the power amps I tried sounded good.  There were only minor differences.  In 1993 I ended up selecting the Classe’ 70 because it sounded slightly better to me than the other amps with the Aerius, and because Classe’ has a reputation  for standing behind their product, it was one of the amps Martin Logan used in the lab with the Aerius, and I got a good deal on it.  After 19 years I had some problems with my Classe and ended up switching to a more powerful Chord SPM-1200 (the original version) which can deliver 250watts/channel @8ohms, 512watts @2ohms continuously, and can do more during peaks without distortion.