A Practical Guide to "Class A" (Excellent) Audio Components
By Chuck Hawks
Stereophile Magazine's most popular feature has always been their "recommended components" list. Their selections have often mystified me and are clearly advertiser driven, but I have long admired the concept. An honest, rational approach to such a list that is not influenced by advertisers is practically impossible for a print magazine, which lives or dies depending on advertising dollars, but not for Audio Online, where any single advertiser contributes only a tiny fraction of our income and sharing information with our readers is our only purpose. We have no Board of Directors, owners or publishing company to satisfy.
Class A (Excellent) components are highly desirable when building a personal reference system. Since it is the loudspeakers that primarily determine how any music system sounds, including the best loudspeakers possible in a personal reference system only makes sense. Class A loudspeakers driven by Class B (Good) electronics will sound great and outperform a system using Class A electronics and Class B loudspeakers. A reference audio system is defined by its loudspeakers.
The intent here is not to list every Class A component on the market, but to provide a practical guide to what constitutes Class A and to illustrate this with examples of components at least moderately well known in audiophile circles.
Class A loudspeakers are top of the line products. To be in Class A, conventional moving-coil loudspeakers must have sizeable woofers capable of moving enough air to make low frequencies audible. In practical terms, that means at least 150 sq. in. of woofer surface area. (Three 8" = 151 sq. in., one 14" = 154 sq. in., two 10" = 157 sq. in., one 15" = 177 sq. in.; two 11" = 190 sq. in.; three 9" = 191 sq. in.) The woofers should have cast aluminum frames for rigidity, powerful magnetic structures and large diameter voice coils.
Cone tweeters are directional; that is, limited in angular dispersion (coverage). For this reason, Class A systems usually use dome, ribbon or horn tweeters. To eliminate distortion at the crossover point(s), the number of crossovers should be minimized. For example, a two-way system is preferred over a three-way system.
Class A loudspeakers should be wide range systems, offering an on axis frequency response of at least 39-20,000 Hz +/- 3 db. They should be capable of reproducing fundamental tones below 40 Hz at no more than -3db without recourse to a separate subwoofer module.
To play loud enough to even come close to live music sound pressure levels in a medium size listening room (listening position 15' from speaker), the Class A speaker system's sensitivity should not be lower than 90db SPL (one watt at one meter). Sensitivity in excess of 95db is highly desirable. Some loudspeakers, for example the Vandersteen Model Seven and the Genelec Main Monitors, come with built in power amplifiers to overcome their low sensitivity.
The enclosure must be correctly designed, very well-made and designed to suppress resonances. Naturally, the overall sound reproduction must be exceptionally accurate. Class A speakers are almost always floor standing designs in order to meet these requirements. (A bigger enclosure ameliorates other problems.) Here are examples of some currently produced loudspeakers that qualify:
Pre-Amplifiers, Power Amplifiers, Tuners and CD players
Pre-amplifiers, power amplifiers and tuners have few moving parts, generally just knobs and switches. However, they must be extremely well made, carefully assembled using top quality parts and should last for decades. Only discreet pre and power amplifiers can be considered for Class A. Integrated amplifiers are, by their nature, relegated to Class B or lower.
The best pre-amplifiers are very quiet in operation. Total distortion should be extremely low, usually less than 0.05%, and the signal to noise ratio should approach 100db for line level inputs. Most will include good moving magnet (MM) phono pre-amplifier circuitry. The frequency response from 20-20,000 Hz should be nearly flat, perhaps +/- 0.5db.
Power amplifier excellence is not a matter of high output power, it is a matter of quality and excellent performance (accurate amplification of the input signal). Full rated RMS power should be available from 20-20,000 Hz with both channels driven. Frequency response should be within +/- 1db or better, 20-20,000 Hz. Distortion of all types should be very low, not greater than 0.5% and typically less. The signal to noise ratio at rated output should be 85db or better. (Some approach or exceed 100db.) The higher the damping factor the better. Be aware that the way specifications are measured and stated varies among manufacturers.
Many excellent stereo power amplifiers are "dual mono" designs. These are essentially two mono amplifiers with a common front panel and power cord. Other power amplifiers are monoblocks (monaural), which means that two are required for stereo operation.
Many of the electronics manufacturers listed below also offer state of the art compact disc (CD and SA-CD) players. The audiophile seeking an excellent CD player need look no further than a Class A electronics manufacturer. Here are some manufacturers that currently produce Class A electronic components:
Turntables and Tonearms
Turntables are electrically powered, but the key to turntable excellence is superb mechanical design and precision manufacturing. Class A turntables are top of the line wonders of low friction, low resonance mechanical function/operation. They are all single play units, although some may offer automated tonearm operation. Record changers are outdated in high-end audio. The best turntable designs go to great lengths to minimize rumble, wow and flutter.
A few companies, such as SME and Ortofon, specialize in manufacturing state of the art tonearms that can be adapted to a variety of manual turntables. Long radial tonearms potentially track more accurately than shorter tonearms and low tonearm mass is very desirable.
The pick-up cartridge traces the grooves in an LP record and generates an analog electrical signal that is fed to a phono pre-amplifier. Thus, the cartridge and tonearm relationship must be synergistic. This is why some Class A turntables come with tonearms and cartridges installed and some turntable manufacturers offer optional matched tonearms and/or cartridges.
Audiophile phono cartridges have become expensive, separate tonearms have always been pricey and Class A turntables cost even more. A complete Class A turntable system represents a substantial investment in vinyl record playback. Following are some companies that offer Class A turntables and tonearms. Note that most also offer less expensive models:
Copyright 2011, 2012 by Chuck Hawks. All rights reserved.