A Re-Introduction to Two-Channel Stereo (Part 5: Amplifier)

Time to get serious by placing the amplifier, or power amplifier, in its proper context. As the final electronic component in the chain from original recording to loudspeakers, the amplifier’s job is to increase the power of the signal, or simply, to make everything louder. For better or for worse. Better: high quality original recording, high-quality turntable / cartridge / phono stage or CD player, pre-amplifier, and high quality interconnection cables running between these devices. Worse: the inadequacies of the weakest link are amplified, too.

In the previous article, we discussed a $999 Rotel pre-amplifier, the RC-1570. Happily, this component was designed to pair with the same company’s RB-1552 Mk II, also $999. (Each can be used with a component from another company, but they look and sound good together—and they’re available in a choice of silver or black.). The RC-1570 is a 130 watt amplifier—a 200 watt version is available for $600 more as the model RB-1582 Mk II—useful if your loudspeakers require more power.

Here's a look inside the Rotel RB-1552 MkII with the large transformer common to power amps.

Here’s a look inside the Rotel RB-1552 MkII with the large transformer common to power amps.

How much power do you need? The answer depends upon several factors. The first is the size of the room—think cubic feet, not square feet. A small room—let’s say 10 feet by 15 feet with an 8 foot ceiling—that’s 1,200 cubic feet would require about 50 watts per channel, more if you’re driving a pair of speakers with a special power-consumptive design (the Magnepan series of flat panel speakers are an example). A good-sized living room (20 x 20 x 10 feet = 4,000 square feet) requires about 100 watts per channel—more if you play your music loud. Bigger room, more power required. However: if your room’s acoustics are “dead”—tapestries on the walls, lots of soft absorbent furniture, thick carpeting, few exposed reflective surface—you may need more power. And if your room is very “live,” you may need less power.

If this seems complicated, trust your ears. Ask your dealer to arrange an in-house test so that you can listen to the prospective amplifier and loudspeakers in your listening room. You will learn a lot about the relationship between the amp and the speakers. (More about listening rooms in the next article.) Be sure to listen to your own records, your own CDs—music whose sound you know from past experience.

Start with the low register: the bass, the drums, the bass section of the orchestra, the lowest vocal sounds. If the amp is suitable to the room and the speakers, the bass will be clearly defined—and thrilling. If you sense some straining, or graininess, then the amp is insufficient for the speakers’ needs (this is why your in-home demo ought to include a test of an amplifier beyond what you believe you need). Now, listen for the soundstage—the placement of the instruments, the sense that you are listening to a full group, ensemble or orchestra. When the music becomes complicated, does the amplifier keep up, or does the soundstage begin to decompose? Start at a lower volume, then gradually increase. If the music sounds very good at a low level, you’ve got a good match between speakers and amplifier. If the music doesn’t sound as good when the volume increases—is the higher register smooth or does it become edgy (and, perhaps, headache-inducing)? Don’t be afraid to go louder than you might listen to under normal circumstances—you want to push the system near its limits (preferably under dealer supervision so you don’t blow out the speakers). Listen to a variety of recordings in order to expose both strengths and weaknesses. And by all means, step up to a better amp in order to understand what you are and are not buying.

For most listeners, most of the time, the Rotel RB-1552 Mk II will be an ideal choice, but it’s considered an entry level amplifier for high-end audio, as is the competitive Parasound A-23 Halo (also $999) for comparison. If you were to increase your investment to about $2,300, and your room, listening preferences and/or loudspeakers require the additional power, you should certainly consider Parasound’s 250-watt A-21 Halo. And, take note, there is a sister pre-amp ($1,095), the well-reviewed Parasound 2-channel P5.

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To learn more about any audio component, download the owner’s manual before you buy. (Click on picture.)

Here, we begin to understand the passions of an audiophile: the resonances of the cello, the timber of the piano, the breath behind the vocals, the feeling of warmth and presence, all of these indescribable factors come together to more than justify the additional investment. It’s tempting to read the engineering background, and to refer to the design of the transformer, or the capacitors, or the overall approach to technology, but for me, none of that matters much. Most equipment in this price class is well-made, and most benefits from sophisticated engineering design, but it’s very difficult for me to understand these technology discussions. And besides, what I hear—and I do spend a lot of time listening, as you should if you’re making this kind of investment—and I’ve learned to trust my ears, my brain’s ability to process the information, and the holistic feeling that each recording seems to offer. I think the Rotel sounds very good, and the Parasound A-23 sounds even better—for all of the reasons described above. They also sound different from one another, but I cannot fairly detail the differences because I listened to these models in different rooms, with different loudspeakers.

img_0903Too theoretical? Maybe. We can shift back to the practical side of technology. These amplifiers—typical of their class—offer both RCA and XLR (“balanced”) inputs. It’s best if your pre-amp and your amplifier are both equipped with balanced connection. In the high-end community, there is no clear consensus in favor of balanced connections, so try both to determine which approach you prefer.

The other big decision: tube vs. solid state design. Certainly, tubes can sound sweeter, but solid state may seem less, well, scary. This is a longer discussion for a future article. My short-form recommendation: a tube pre-amp paired with a solid stage amplifier—but there’s lots more to discuss.

img_0902If you’d like to dig deeper into the world of amplifiers, that’s a good reason to buy The Complete Guide to High-End Audio by long-time Stereophile writer Robert Harley (now in its fifth edition. Some of the information in the book is fairly technical, but most of it is written for the same reason I’m writing these articles—to help select the best listening equipment.

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  1. […] 2 – Basic Loudspeakers 3 – Integrated Amplifiers 4 – Pre-Amplifiers 5 – Amplifiers 6 – Listening […]

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