On Power Amplifiers and How Much Power

By Bryan Geyer

The power amplifier needs to accurately amplify (apply voltage gain to) the incoming signal, and deliver that amplified signal, fully in tact, to a designated low impedance load. The power amplifier is not supposed to alter or reshape the input signal in any other manner, so optimum accuracy can be enhanced when the potential for error (a.k.a. distortion) is effectively suppressed.

There are, today, many solid-state power amplifiers that are highly accurate. They replicate the input signal with extremely low error, so it’s virtually impossible to separate such amplifiers by merely listening; they’ll simply sound identical. Distinguishing differences generally involve power output capability, load impedance compatibility, basic circuit design (and choice of active components), intended reliability, and target market. One needs to push deeper into the technical detail to make sensible decisions about benefit-versus-cost aspects; listening isn’t enough.

Given this state of modern amplifier excellence, it’s unrealistic to expect equivalent accuracy from vacuum tube dependent design. The archaic limitations of the triode tube (Lee DeForest, 1906) are not consistent with contemporary medians. Ruler-flat power response, near-zero (<  0.1%) total harmonic distortion (THD) at full rated power, and ultra-low output impedance (~ 1/10th the Zout of a typical tube amp) is now routine in the case of most solid-state power amplifiers. Identical measurements made on the very best vacuum tube models show that they can’t approach the same readouts. For example, consider THD: Typical “high-end” tube-type audio power amplifier THD limits are ~ 16X to 50X worse than as specified for a popular “mid-market” solid-state power amplifier.* (They’re 1% to 3% THD instead of 0.06% max.) That’s undeniable regression. Of course, tube boosters assert that this shortcoming is actually beneficial. They claim that vacuum tube amps will thereby render a warmer, more euphonic (?) sound. Given this Zen-infused perception, tube power amplifiers can seemingly transcend their intended role and become creative (but arbitrary) signal processors. This uncontrolled mutation is not consistent with the initial (accuracy) objective.

I recommend a power amplifier that can accurately replicate the input signal, and do so with sufficient power to deliver some +2 dB to +3 dB more unclipped drive than your speakers can tolerate. A speaker system’s safe operating range is defined by its “maximum unclipped power input” limit. The application of some +2 to +3 dB margin for power amplifier output will then assure that your speakers never see a clipped (potentially destructive) input signal that’s within the speakers’ safe operating range. E.g.: If your loudspeakers are able to accept unclipped power input ≤ 80 Watts, then your power amplifier should be able to provide unclipped power output ≥ 127 Watts (+2 dB) or ≥ 160 Watts (+3 dB). In this example, do take note that the cited power levels may be appreciably more than many tube-type power amplifiers can produce. Vacuum tube power amps are wimpy, as well as grossly inefficient.

Apply that “euphonic polishing” later, at the loudspeaker stage. The speakers’ performance will be inseparably linked to the acoustic characteristics of your listening room, so it’s sensible to address both of those issues together—without the need to compensate for anomalous amplifier sound.                                                                       

*Parasound’s Halo A23+ power amplifier ($1,495 list) versus the best from PrimaLuna, VTL, and VAC.

BG (February 2019)

No comments:

Post a Comment

Meet the Staff

Meet the Staff
John J. Puccio, Editor, Publisher, Reviewer

Understand, I'm just an everyday guy reacting to something I love. And I've been doing it for a very long time, my appreciation for classical music starting with the musical excerpts on the Big Jon and Sparkie radio show in the early Fifties and the purchase of my first recording, The 101 Strings Play the Classics, around 1956. In the late Sixties I began teaching high school English and Film Studies as well as becoming interested in hi-fi, my audio ambitions graduating me from a pair of AR-3 speakers to the Fulton J's recommended by The Stereophile's J. Gordon Holt. In the early Seventies, I began writing for a number of audio magazines, including Audio Excellence, Audio Forum, The Boston Audio Society Speaker, The American Record Guide, and from 1976 until 2008, The $ensible Sound, for which I served as Classical Music Editor.

Today, I'm retired from teaching and use a pair of bi-amped VMPS RM40s loudspeakers for my listening. In addition to writing the Classical Candor blog, I served as the Movie Review Editor for the Web site Movie Metropolis (formerly DVDTown) from 1997-2013. Music and movies. Life couldn't be better.
Karl W. Nehring, Contributing Reviewer

For more than 20 years I was the editor of The $ensible Sound magazine and a regular contributor to its classical review pages. I would not presume to present myself as some sort of expert on music, but I have a deep love for and appreciation of many types of music, "classical" especially, and have listened to thousands of recordings over the years, many of which still line the walls of my listening room (and occasionally spill onto the furniture and floor, much to the chagrin of my long-suffering wife). I have always taken the approach as a reviewer that what I am trying to do is simply to point out to readers that I have come across a recording that I have found of interest, a recording that I think they might appreciate my having pointed out to them. I suppose that sounds a bit simpleminded, but I know I appreciate reading reviews by others that do the same for me -- point out recordings that I think I might enjoy.

For readers who might be wondering about what kind of system I am using to do my listening, I should probably point out that I do a LOT of music listening and employ a variety of means to do so in a variety of environments, as I would imagine many music lovers also do. Starting at the more grandiose end of the scale, the system in which I do my most serious listening comprises an Arcam CDS50 CSD/SACD CD player, Goldpoint SA4 Passive Preamp, Legacy Audio PowerBloc2 amplifier, and a pair of Legacy Audio Focus SE loudspeakers. I also do a lot of listening while driving in my 2016 Acura RDX with its nice-sounding ELS Studio sound system through which I play CDs (the ones I especially like I rip to the Acura's hard drive so that I can listen to them whenever I want) or stream music through the system using my cell phone. For more casual listening at home when I am not in my listening room, I often stream music through the phone into a Vizio soundbar system that has remarkably nice sound for such a diminutive physical presence. And finally, at the least grandiose end of the scale, I have an Ultimate Ears Wonderboom Bluetooth speaker for those occasions where I am somewhere by myself without a sound system but in desperate need of a musical fix. I just can't imagine life without music and I am humbly grateful for the technology that enables us to enjoy it in so many wonderful ways.
Bryan Geyer, Technical Analyst

I initially embraced classical music in 1954 when I mistuned my car radio and heard the Heifetz recording of Mendelssohn's Violin Concerto. That inspired me to board the new "hi-fi" DIY bandwagon. In 1957 I joined one of the pioneer semiconductor makers and spent the next 32 years marketing transistors and microcircuits to military contractors. Home audio DIY projects remained a personal passion until 1989 when we created our own new photography equipment company. I later (2012) revived my interest in two channel audio when we "downsized" our life and determined that mini-monitors + paired subwoofers were a great way to mate fine music with the space constraints of condo living.

Visitors that view my technical papers on this site may wonder why they appear here, rather than on a site that features audio equipment reviews. My reason is that I tried the latter, and prefer to publish for people who actually want to listen to music; not to equipment. My focus is in describing what's technically beneficial to assure that the sound of the system will accurately replicate the source input signal (i. e. exhibit high accuracy) without inordinate cost and complexity. Conversely, most of the audiophiles of today strive to achieve sound that's euphonic, i.e. be personally satisfying. In essence, audiophiles seek sound that's consistent with their desire; the music is simply a test signal.

William (Bill) Heck, Contributing Reviewer

Among my early childhood memories are those of listening to my mother playing records (some even 78 rpm ones!) of both classical music and jazz tunes. I suppose that her love of music was transmitted genetically, and my interest was sustained by years of playing in rock bands – until I realized that this was no way to make a living. The interest in classical music was rekindled in grad school when the university FM station serving as background music for studying happened to play the Brahms First Symphony. As the work came to an end, it struck me forcibly that this was the most beautiful thing I had ever heard, and from that point on, I never looked back. This revelation was to the detriment of my studies, as I subsequently spent way too much time simply listening, but music has remained a significant part of my life. These days, although I still can tell a trumpet from a bassoon and a quarter note from a treble clef, I have to admit that I remain a nonexpert. But I do love music in general and classical music in particular, and I enjoy sharing both information and opinions about it.

The audiophile bug bit about the same time that I returned to that classical music. I’ve gone through plenty of equipment, brands from Audio Research to Yamaha, and the best of it has opened new audio insights. Along the way, I reviewed components, and occasionally recordings, for The $ensible Sound magazine. Recently I’ve rebuilt--I prefer to say reinvigorated--my audio system, with a Sangean FM HD tuner and (for the moment) an ancient Toshiba multi-format disk player serving as a transport, both feeding a NAD C 658 streaming preamp/DAC, which in turn connects to a Legacy Powerbloc2 amplifier driving my trusty Waveform Mach Solo speakers, supplemented by a Hsu Research ULS 15 Mk II subwoofer.

Mission Statement

It is the goal of Classical Candor to promote the enjoyment of classical music. Other forms of music come and go--minuets, waltzes, ragtime, blues, jazz, bebop, country-western, rock-'n'-roll, heavy metal, rap, and the rest--but classical music has been around for hundreds of years and will continue to be around for hundreds more. It's no accident that every major city in the world has one or more symphony orchestras.

When I was young, I heard it said that only intellectuals could appreciate classical music, that it required dedicated concentration to appreciate. Nonsense. I'm no intellectual, and I've always loved classical music. Anyone who's ever seen and enjoyed Disney's Fantasia or a Looney Tunes cartoon playing Rossini's William Tell Overture or Liszt's Hungarian Rhapsody No. 2 can attest to the power and joy of classical music, and that's just about everybody.

So, if Classical Candor can expand one's awareness of classical music and bring more joy to one's life, more power to it. It's done its job. --John J. Puccio

Contact Information

Readers with polite, courteous, helpful letters may send them to classicalcandor@gmail.com

Readers with impolite, discourteous, bitchy, whining, complaining, nasty, mean-spirited, unhelpful letters may send them to classicalcandor@recycle.bin.

"Their Master's Voice" by Michael Sowa

"Their Master's Voice" by Michael Sowa