On LED Flashlights…

By Bryan Geyer

The innate connection between a flashlight and “Audio Tech
Talk” becomes apparent as soon as you try to inspect any part of your sound
system that lies beyond the front panel. In recognition, here’s some personal
guidance about the most vital tool you’ll ever need: A modern single-cell LED
flashlight.

First, learn why the light emitting diode (LED), a
semiconductor device that dates to the late 1960s, didn’t become abundant in
flashlights until some 30 years later. What a curious delay! What happened? And
what changed? Well, a modern “white light” LED won’t fire until it sees a
threshold bias of about 3.2 volts minimum, and 4 volts or more works better.
But a fresh single cell battery produces only ~ 1.2 to 1.7 volts, dependent on
its chemistry (see footnote*), so multiple batteries would be needed to
fire a solitary white light LED. Clearly, using more batteries than before
didn’t advance the state of flashlight design, so miniature incandescent lamps
endured. Then, barely before year 2k arrived, integrated circuit “boost chips”
appeared. These new silicon ICs could efficiently elevate the energy from a
single storage cell to the operating level needed to fire a white light LED.
The basic design concept was old, but implementing it in IC form was
breakthrough genius. The entire boost function, consisting of the surface-mount
chip plus some tiny passive peripherals, could now be packed into a bundle
smaller than the size of two stacked dimes. A practical single AA cell LED
flashlight was suddenly viable, and its launch assured immense advantage over
anything using an incandescent bulb. A lone LED could now provide more light
(with selectable lower levels), draw less current, offer high resistance to
shock and vibration, and assure decades (not hours) of maintenance-free service
life—all while selling at competitive mass-market prices.

Product development was intense, with many players engaged.
Some failed, some flourished, and several smart trans-Pacific sources became
dominant. There’s now a wide array of LED flashlights and multi-LED lanterns on
the market. Many designs serve niche applications, but my intent here is to
feature a basic everyday flashlight—a modestly priced model that’s appropriate
for general purpose use and practical in-pocket carry. A flashlight that…

…is short (≤ 3.1" long), skinny (≤ 0.75" diameter),
and uses only a single AA size cell.

…is blindingly bright at full output, with multiple lower
levels to conserve current drain.

…has long throw capability, with enough side spill to see the
borders of your path at night.

…is obvious in operation, with a single butt-end control
button for all switching functions.

…offers instinctive battery exchange: unscrew head and
replace AA cell, button end up.

…has solid mechanical integrity; built to withstand the
rigors of moderate abuse.

…if supplied with a pocket clip, such clip must be readily
removable and leave no evidence.

… meets the IP68 waterproof standard (up to 30 minutes at
depths of ≤ 2 meters).

…is cheap enough stash extras (toolboxes/cars/bikes/garage)
and give as gifts.

There aren’t a lot of candidates that meet all of my
objectives. Many come close, then fail the “side spill” criteria. That’s
because flashlight marketers always hype throw (range), and inexperienced
buyers focus on that feature; they haven’t yet grasped the importance of spill
(beam spread). The two parameters (throw and spill) are mutually exclusive;
more of one means less of the other. A very tight beam will deliver impressive
reach, but hot spot fixation invites personal risk when you can’t see the edges
of a narrow path from just one step away.

My pick as a good “everyday” single AA cell flashlight is the
Fenix E12 Version 2.0. It meets all of my criteria, and you can buy it
here: https://www.fenix-store.com,
or here: https://www.batteryjunction.com
The Fenix E12 V2.0 flashlight offers three selectable outputs: 5, 30, and 160
Lumens. It uses a cool white LED, and has an ultra-thin (3mm) optical front
lens—all very desirable. The lowest level is appropriate for checking your
watch in a darkened theater or finding a keyhole at night. The mid-level
setting, 30 Lumens, assures a practical balance between output and capacity.
It’s great for all of your “fix it” tasks, also for walking at night. The full
160 Lumen output provides a brilliant spotlight, but keep it brief! Apply only
in 10 to 20 second transient bursts. At this level, supply current is consumed
at a rapid rate, and there’s significant internal dissipation (heating). As
with many LED flashlights, these output levels are all electronically
regulated, so the lighting intensity stays constant; it won’t droop as the AA
cell ages. Full expiration becomes suddenly apparent; it’s dependent on the
drain that’s required for the level you’ve selected. When the supply current is
insufficient for a given level, the output will drop to the next lower level.
When it’s too low to maintain the regulated 5 Lumen minimum, the output drops
to a useless glow, then goes out.

The Fenix E12 V2.0 flashlight comes with an attached (by
compression) pocket clip that I dislike, so I trash it. This is easy to do with
the aid of pliers—just grab the clip and pull it off. It will readily detach
and leave no evidence that it was once mounted on the flashlight body. This
flashlight is so small and light that a pocket clip isn’t of practical benefit;
however, removing the clip will then expose a perfectly cylindrical body, and
round stuff that’s not restrained can roll off flat surfaces. If this annoys
you, consider mating a wrist strap to a rear lug. Straps that have a small
pigtail loop at the end will pass through the lug without impeding the control
button.

BATTERY OPTIONS: AA cells are readily available in the
variants (3) noted below*, but you’d do well to reject the use of
alkaline (manganese dioxide) LR6 cells. These conventional cells are very
popular, but too risky to merit informed consideration. When an alkaline AA
cell approaches expiration (output ≤ 0.7 volts), it will progressively
destabilize and form a caustic compound (KOH, potassium hydroxide) that will
penetrate the outer shell and attack anything that’s within reach. The
consequent damage can be severe. This is an inherent flaw—all alkaline cells
present this same inevitable hazard—so don’t use alkaline AA cells.
Instead, select either of the other options. I use the non-rechargeable
lithium-iron disulfide Class FR6 cells, e.g., Energizer’s “Ultimate”**.
Others prefer the rechargeable nickel metal-hydride (NiMH) Class HR6 cells.
Both options are safe, don’t leak, and work well. Non-rechargeable lithium AA
cells exhibit extended operating life, perform well in cold ambients (alkaline
cells don’t), weigh about 40% less than the alkaline equivalent, and can
tolerate long term (10 years) passive storage with minimal (5%) net
self-discharge. Buy in bulk, stow for use as needed.

* The nominal AA cell output voltage,
when fresh (or freshly charged), is…

…1.5 volt for a non-rechargeable alkaline (manganese dioxide)
IEC Class LR6 cell.

…1.2 volt for a rechargeable nickel metal-hydride IEC Class
HR6 cell.

…1.6 to 1.7 volt for a non-rechargeable lithium-iron
disulfide IEC Class FR6 cell, e.g., Energizer “Ultimate” AA cells.

IEC = International Electrotechnical Commission

 ** I buy on-line, from Battery Junction;
refer… https://www.batteryjunction.com/energizer-aa-ln91-24pk-battery.html

BG (December 2022)

In the Golden Age

By Bill Heck
 

Ah, to have lived in the Golden Age of…well, anything. The Golden Age of philosophy? Ancient Athens, hobnobbing with Socrates, Plato, and Aristotle. Less ambitiously, there’s the Golden Age of American literature: maybe the mid-20th century, when we could hang out with Faulkner and Hemingway, or perhaps earlier so we could look over Melville’s shoulder. There’s even a Golden Age of American Industry for a few postwar decades, when American industrial might was unchallenged and a husband (it was always a husband, wasn’t it?) could provide for an entire family with a single factory job.
 
Then there was the Golden Age of American Classical Music, in the pre-WWII and postwar eras when giants roamed the land: Reiner, Szell, Ormandy, and Stokowski and their city orchestras, when first radio and then television networks competed to be highbrow: NBC even had its own symphony orchestra!
 
And the Golden Age of High Fidelity? Well, that could have been in the 1950s – 60s when the classic Marantz, McIntosh, KLH and then Advent appeared, or perhaps in the 1970s – 80s when exotic “high end” brands arose, tubes all aglow: Audio Research, Conrad-Johnson, Mark Levinson.
 
You may have noticed that all these Golden Ages have something in common: they happened in some magical past. We hear that philosophy has been all downhill since those smart Greeks; literature has succumbed to the way of Kindle; classical music is a mere footnote to popular culture; American industry is a shadow of its former self. And audio? Alas, High Fidelity has given way to MP3 and earbuds, with a few remaining enclaves accessible only to those with megabucks for gigantic amplifiers and massive speakers – and even multi-thousand dollar cables!

I won’t try to speak for philosophy or literature or even manufacturing, but there’s something odd about the tales of the demise of classical music. If serious music is sunk, how is it that we see a steady stream of classical recordings being released each and every week? And how is it that even newly minted musicians, those so obscure that only their mothers have heard of them, amaze us with their talents on a daily basis? Listen critically to some of those giants of yesteryear: Schnabel and Richter were known to hit some clinkers, and some of those legendary orchestras seemed occasionally lost in thickets of (sometimes wrong) notes. The level of accomplishment of even the rawest rookies these days is amazing, as they confront works formerly thought nearly unplayable and toss them off with ease. Orchestras in cities that you never heard of could play rings around some of the fabled bands of a few decades ago. And wait – how is it that those cities you never heard of even have orchestras? Still more: what about those contemporary composers who are once again writing music that ordinary music lovers actually want to hear? While there’s no denying that the classical music world has issues to confront, in many ways we are in the Golden Age of Classical Music: more music, and more ways to access it, than ever before.
 

But what about the Golden Age of High Fidelity? It’s true that earbuds and Alexa speakers get the headlines. It’s also true that many of the stereo shops of a decade or two ago have gone the way of the dodo, and too many of those that remain seem to specialize in multi-channel systems optimized to produce the sounds of car chases, laser weapons, and earthquakes. But quietly, behind the scenes, we have entered a true Golden Age of High Fidelity sound reproduction. And you, my friend, are the beneficiary.
 
So what do I mean by a “Golden Age?” Just this: audio equipment has evolved to a point at which:
 
· it is easy to obtain music sources – and the equipment to play those sources – that would have provoked awe just a few years ago; and
· doing so requires less specialized knowledge, effort, and commitment than ever before; and
· those sources and equipment are available at extraordinarily low cost, affordable to those with even moderate incomes.
 
Let’s take these in order, starting with the sources and equipment. Incredibly, the CD standard, developed back in 1980, has turned out to be capable of music reproduction that is rarely surpassed. Perhaps some people do hear small differences between CD and “high resolution” audio, although evidence beyond mere assertion is spotty, but the real point is that the plain old CD standard is remarkably robust and satisfying.
 
Moreover, a little listening should convince you that recording processes and techniques now routinely deliver superb results – not perfect, and of course some recordings are better than others, but a high percentage of contemporary recordings sound very good. Yes, some (a few) older recordings still hold their own, but the batting average seems much higher these days, and the best of today surely equals or even – oh heresy! – surpasses those fabled recorded masterpieces of yesteryear.
 
Meanwhile, even the best recordings need to be played back through a good sound system. Here again, the technological progress has been astounding. CD players, digital-to-audio converters (DACs), music streaming devices, preamplifiers and amplifiers now boast specifications and performance so good that it is difficult to find measurable or demonstrable audible differences among them. Yes, I know that the previous sentence invites derision and flaming comments from those convinced otherwise by the incessant advertising that passes for audio reviewing in some quarters. But even bastions of audio perfection like The Absolute Sound seem to admit, albeit sometimes reluctantly and only between the lines, that many humble components are really, really good. Meanwhile, the more objectively oriented world, as represented by sites like audiosciencereview.com, produce both measurements and listening results that indicate staggeringly good performance over and over. The point is not that “everything sounds the same,” but rather that excellence is readily available.
 
Turning to my second point above, the mere availability of first-rate components isn’t much help if you need to spend months or years learning enough to identify them, more months looking for them, and a lifetime learning to adjust and tweak them to optimize their performance. Who has time for that?
 

But, in fact, high quality components are easy to find. As the quality of even entry level components has skyrocketed, the problem of finding good stuff has decreased proportionally: if many components are now pretty good, your odds of finding satisfactory ones are high. We have not reached that state of audio nirvana in which components are indistinguishable commodities, but consider the contrast with even the recent past. Back in the earlier supposed golden ages, say the 1970s, the typical audiophile might haunt electronics shops weekend after weekend, searching for that elusive combination of components that would work well together, the strengths of each offsetting the weaknesses of the other. And let’s not even get started on craziness like adjusting tube bias or figuring out which transformer tap worked best with which speakers. (If you have no idea what I’m talking about, consider yourself lucky.) In the more recent past, the search may have been easier, but one at least needed to identify multiple types of components, learn the function of each and how to connect them, and assemble complementary units into a working system. Now consider something like the NAD C 658 unit that I reviewed some months back: it’s one box. That’s it. Oh wait, you need an amplifier; if that’s too complicated, you can purchase a similar unit that combines most or all of this same functionality plus the amp into one box. But wait, don’t you need a CD player? Not even that. Instead, you can use streaming to pull music out of thin air, so to speak, at CD or higher resolution.
 
And that brings us to the third point: low cost. Let’s build a simple, low cost system; I’ll refer to a few brands as examples, but please understand that there are plenty of choices that would be highly satisfactory.
 
First, we’ll use a streaming unit. You could get something like the Bluesound PowerNode, which combines streaming with an integrated amplifier for just under $1,000 (less for a perfectly good used unit), or any of a number of similar units, or even separate streamers and amplifiers, for not much more. For that price, you get competent audio streaming at high resolution and sufficient power to drive some decent speakers.
 
The contrast with previous alleged Golden Ages is stark. Oh sure, those lovely Marantz tube units back in the 1960’s were only hundreds of dollars – but in real dollars, i.e., accounting for inflation, prices for high quality audio equipment that have never been lower. (And remember, in those halcyon days of yore, you needed both a preamp and power amp, along with a turntable with tonearm and cartridge.) Moreover, those old tube units required periodic and often expensive maintenance and adjustment: replacing tubes was a periodic ritual. In addition, those of us of a certain age remember when every small town had at least one electronics repair shop, needed because those old electronics broke with distressing regularity. Modern solid-state stuff, not so much.
 
You still need speakers, and again it is technology to the rescue. Advances in science and engineering have made formerly exotic materials available and usable at low prices, and advances in computation have made formerly onerous and time-consuming design work much easier and faster. The result is a generation of widely available, reasonably priced, high-performance speakers. Of course, you can spend a lot on speakers, and expensive speakers often (though not always) yield better performance, but you can get into the game with very good speakers at very low prices. Let’s start you out with speakers at $1,000: they won’t shake the room with thunderous bass or wake up the dog with ultra-high frequencies, but they can sound quite credible in a basic system.
 
Our total allocation so far is around $2,000 brand new, full retail. (Lest you think such a number totally outrageous, just consider that a high-end television can easily be more.) Not pocket change, but as a long-term investment, not eye-watering either. If you find used equipment, subtract some more. Will you be satisfied forever? Maybe; if not, you can improve things incrementally, again at low cost, in one or more of the following ways.
 
· Upgrade the speakers. This is the obvious place to start: the possibilities – and the price levels – are endless. At our introductory cost level, even small increments in price will buy you significant upgrades in sound.
· Add room correction: This can produce major gains; one easy option is a $400 – 500 standalone unit from the likes of miniDSP. Alternatively, spend a little more up front and some streaming units include room correction for free.
· Add a CD player: as the streaming device likely has a digital input, you can get away with a cheap or used player functioning only as a transport. $100 - 200?
· Add a subwoofer: There are plenty of competent choices starting well under $1,000.
 
Finally, there’s the music. You can have high-quality audio streaming for a dirt cheap $10-15 per month. Even if that price doubles or triples (to better support the musicians), it’s still cheap, especially considering that the monthly fee buys you access to a library of hundreds of thousands of albums – audio nirvana indeed.
 
Does all this make our own time the Golden Age of Audio? There are those who say no, who lament the fact that it’s too easy; who long for the days when, by golly, you really had to work to put together your audio system; who whine that it doesn’t count if you don’t have to spend endless hours getting it right (or even getting it working at all). It’s the same syndrome as with the golden age of cars: those Jaguars, MGs, Triumphs, early Corvettes were so beautiful, so fun, symbolizing the freedom of the open road. I understand that nostalgia, and I, too, feel the appeal of those early cars – until I want to go somewhere. By any objective measure, today’s cars are better than those vehicles of yesteryear: more reliable, faster, mostly better handling, more economical, safer, etc. Similarly, we can understand the appeal of glowing tubes, monster amps, giant but inefficient speakers – until we just want to listen to music. Is the audio hobby in a golden age? Maybe not, but audio is.
 
A final note:
There are supposed audio gurus who will tell you that putting together a decent audio system condemns you to spending hours and hours tweaking this and that, putting little gizmos that rely on effects unknown to physics on top of and under your components, endlessly comparing freaking wires – and that you most certainly need to subscribe to their YouTube channels and haunt their websites so that they can guide you through this foreign landscape. Forget all that, at least for now. Get the basics under control. If you are inclined to mess around with such things, do so later. (Personally, I recommend that you continue in your blissful ignorance and spend your time listening to music.)
 
Even more annoyingly, there will be those who sneer that you can’t possibly appreciate the nuances of good music because you haven’t spent their threshold amount, whether that’s $10K or $100K, or you haven’t performed the proper rituals or penances of tweaking and fiddling. If that happens, just smile politely, go home, turn on the music, and enjoy your time in the Golden Age of High Fidelity.
 
BH

On Upgrading What’s Analog…

By Bryan Geyer

THE POSIT—Recent
technology advances make it practical to upgrade select analog functions in
many conventional stereo systems. It’s now possible to…
…dramatically extend the range and enhance the
linearity of low bass response.
…materially reduce the mass of the main
speaker enclosures.
…clarify the midrange response by isolating it
from low bass modulation.
…eliminate archaic high-level passive
crossovers that reflect only low order filter slopes.
…enable precise line-level active
crossovers with full 4th order (-24dB/octave) attenuation.

BACKGROUND—The
pursuit of good sound is evolutionary, but the conviction that high fidelity
= big speakers persists. Low frequencies have long wavelengths (28 feet at
40 Hz), so big transducers, in big enclosures, have always been considered
essential to reproduce, propel, and propagate big bass. Regardless, monstrous
monkey coffins that require prominent front-and-center placement look absurd in
domestic living rooms, so reasonable compromise is vital. The usual course is:
(a) downsize the speakers, or (b) always entertain outside, or (c) cram the
system into a “man-cave”, even though the main LR offers superior acoustics
(lower Schroeder frequency), or (d) use headphones only. These are odious
options; let’s pursue better.

WHAT’S CHANGED—In the
mid ’90s, the push to popularize home theater became dependent on finding a
practical way to recreate Godzilla’s footfall while squeezing the mass out of
the additional speaker enclosures. This paradox looked hopeless until design
guru Bob Carver, then at Sunfire, proposed his astonishing new (1997)
self-powered “True Subwoofer” as a viable solution. Market acceptance was slow
until Sunfire’s patent grip was softened; then the trade piled on. The new subs
could pump out pure (low harmonic content) 30Hz sine wave bursts at pressure
levels exceeding anything previously envisioned. Today, relatively compact
subwoofers with only a single 10" or 12" diameter driver (e.g., https://www.jlaudio.com/collections/home-audio-e-sub/products/e112-gloss-home-audio-e-sub-powered-subwoofers-96279)
can produce lower, louder, and cleaner bottom bass (the two bass octaves
below 80Hz) than the very best, biggest, and most expensive full range
floor-standers ever built by anybody, anywhere.

Tempering this marvel
is the reality that these new self-powered subwoofers excel at just one thing:
They can handle those two bass octaves better than any conventional woofer.
They’re able to do that because they’re expressly designed for a single,
solitary mission. They have extremely deep, ultra stiff cones, long and
compliant surrounds with extended x-mass capability, and they’re driven by high
power class D amps that apply carefully contoured equalization. Unlike the
woofers in a costly full range floor-stander, the “sub” doesn’t have to produce
any appreciable output above ~ 140Hz. Conversely, a conventional full range
floor-stander is designed with the expectation that it must also cover the full
low-to-middle bass range, commonly extending to frequencies approaching ~
800Hz, and do so with good linearity. That’s a stringent additional assignment.

TODAY—If the intent
is to achieve optimal fidelity, we need to reconsider how stereo systems should
be configured. Clearly, paired stereo subwoofers* should handle the
bottom bass octaves. The main stereo loudspeakers can then be reduced in size
to reflect the fact that they will no longer have to reproduce those
subterranean sounds. Stand-mount main speakers with 6" to 8" drivers
have proved absolutely optimum. Excellent bookshelf-size speakers, like Harman’s
Revel Performa M126Be (https://www.audioholics.com/bookshelf-speaker-reviews/revel-performa-m126be),
or the Revel M106 (https://hometheaterhifi.com/reviews/speaker/bookshelf/revel-performa3-m106-2-way-bookshelf-monitor-loudspeaker-review-part-one/),
come to mind, and they confer welcome decor relief. The related subwoofers are
best placed near the front corners of the room, at or near floor level, where
they’re generally easy to accommodate. There’s simply no need, anymore, for
monstrous four to five foot tall main speakers that are packed with multiple
10", 12", or 15" woofers. At least, not unless you’re personally
committed to high-end electrostatic-type speakers, such as those
championed by Sanders Sound Systems. (In that event, please see https://classicalcandor.blogspot.com/2019/09/on-elephants-in-room.html.)

In addition to the
cited decor benefit, separating the low bass from the upper bass presents a
compelling aural upside. In a conventional setup, the main woofer and its power
amplifier handle both signals, so there’s often some mild modulation blur of
the upper bass or lower mids when the score calls for a sudden burst of big
bass thunder. Routing that sound directly to the low-pass amplifiers, inside
the self-powered subs, means the main speakers will now be unaffected. The main
power amplifier will never see those low bass signals when they’re appreciably
below the crossover notch. Eliminating this potential midrange modulation is
one of the most vital rewards that you can claim when you add subwoofers and
install an external active crossover. Some listeners feel that the midrange
benefit is even more audible than the subwoofers’ bass extension. Your own
impression might be a bit program-dependent in sensing these complementary
improvements, but it’s clearly evident when the score fits**.

MODERNIZING
CROSSOVERS—A further concern is that conventional full-range speakers impose
the need for accurate driver-level crossover networks. Such filters are
fussy to design and awkward to assemble. They’re wholly dependent on precisely
defined R/L/C components that must pass high current signals to low impedance
loads. Tight tolerance passive parts of this unique nature are rare—most have
no other fundamental application in the scope of the electronics trade, so they’re
often difficult to obtain in the exact values that are needed. The inevitable
consequence of this difficulty is compromise, and compromise breeds inaccuracy†.
Even when they’re effectively designed and constructed, these high level
crossovers often prove inadequate because they’re typically just first order or
second order (-6dB or -12dB/octave) filters with gentle attenuation slopes.
Full fourth order (-24dB/octave) passive crossover networks would be more
suitable, but they become impractical (too complex, physically prohibitive) for
high level (low impedance) applications.

The solution to this crossover dilemma is to move that
function from its classic position, between the power amplifier outputs and the
various driver inputs (where it must process high level signals), to an
earlier point, prior to the power amplifier, where the components will
see only lower line level signals.This
preferred location assures ready access to lots of stable, tight tolerance
R/L/C components of virtually any desired value. When combined with active
op-amp circuitry it’s then possible to form highly selective Linkwitz-Riley
type filters with full 4th order attenuation slopes. The penalty implicit with
inserting the crossover in this line-level position is that a separate power
amplifier will now be needed to connect each crossover output (high pass and
low pass) directly to its designated driver. That means operating in “bi-amplifier”
mode, a form of connection that confers useful advantages; e.g., better load
(driver) damping; also the ability to independently dictate the signal
amplitude sent to each power amplifier.

A fully external
(meaning separately enclosed and powered) active crossover controller is
invaluable when adding supplementary self-powered subwoofers. The active
crossover’s high-pass outputs can feed the main stereo power amplifier +
main speaker system, while its low-pass outputs feed the line inputs on
the self-powered subs. (The active crossover thereby supersedes any built-in
low-pass filtering that might be a part of the sub’s internal circuit, so the
subs should then be operated in their selectable “bypass mode”.) This setup
facilitates convenient adjustment of the “mains-to-subs” dominance (the
relative output levels of the main speakers compared to the subs) from a
single, central location. Without this crossover controller you’d need to crawl
to each individual subwoofer and separately adjust their input sensitivity
controls—and repeat that crawl every time you want to tweak the mains-to-subs
settings or alter the relative channel balance.

An external active
crossover controller with variable frequency capability will allow the user to
position the crossover notch at a point that’s optimum for the main speakers in
use. For most subwoofer setups, this will involve a setting that’s somewhere
between ~ 76Hz and 100Hz. (Lower crossover frequencies are not advisable,
regardless of the main speakers’ perceived bass capability.)

Loudspeaker systems
with internal line-level active crossovers + self-powered class D amps
are already in common use as near-field monitors; also as desk-top setups.
Designs of this nature offering higher power output have also appeared, e.g.,
the “Kii Three”. Clearly, this trend will accelerate. We’re going to see lots
of analog circuitry integrate with the loudspeaker, and some of the speaker
makers are likely to merge with those that currently make power amplifiers. Of
course, vacuum tube power amps—already a moribund species—will then fade forever.
Ditto for big solid-state quasi-class A power amps and heavyweights that
resemble engine blocks. Niche products will always exist, but it’s doubtful
that those who make them will prosper and survive, so be wary about where you
hitch your wagon.

THE PREAMPLIFIER—Refer
https://classicalcandor.blogspot.com/2019/12/on-controlling-volume.html.
Amen.

Footnotes…
*Paired stereo subwoofers (not a solo “shared
bass” subwoofer) are essential for acoustic advantage; refer https://classicalcandor.blogspot.com/2019/03/basics-about-bass_20.html.

**Re. “when the score fits”…is a phrase
that brings to mind a subwoofer quirk that you need to know. Many (all?) of the
companies making self-powered subs provide the useful ability to select
automatic “signal sensing” as a means of activating the sub’s internal power
amplifier; i.e., to auto-awaken the sub from its passive sleep state. In sleep
mode, the sub stays on, but it dissipates minimal power until it perceives that
it’s time to rumble. The sub then goes into active mode, and remains active
until there’s no input signal for an appreciable duration, e.g., 20 or 30
minutes. An initial problem is sometimes evident with respect to the maker’s
signal-sensing level. Bear in mind that the sub can only hear very low
frequency signals because its line-level input path is through a low-pass
filter. When there’s persistent heavy bass (as with virtually all pop music
today), the sub will awaken quickly. But when the bass content is evident only
where Mozart scored it, that sub might not awaken (go active) until you’re a
third through an extended concerto. Classical music just doesn’t exhibit the
same pounding bass line that persists with pop. Unfortunately, the folks that
make subs think classical music is extinct, so they normally set the signal
sensing to trigger at a higher (less sensitive) level than what’s optimum for
classical format. In many cases the original factory setting is as much as 14dB
to 16dB too high (too insensitive). So—when you buy a sub, communicate with
your supplier. Have the maker set your subs to auto-activate when The Lark [is
barely] Ascending. (I bow to Mr. Vaughan Williams.) If they fail to do
this you’ll then need to return your subs to the source, and have a factory guy
readjust the trip point (warranty return, maker’s expense). With all of the
subs that I’ve seen, this setting is always an internal adjustment. Some subs
might now make this tweak externally accessible, but internal-only is more
logical because it’s a “set once” consideration, and external access invites
misuse. Home-based DIY readjustment is definitely not feasible. The internal
class D “plate amp” has complex multi-layer boards + tiny surface-mount (not “through-hole”)
components, and that makes this simple task too risky when no schematic is at
hand.

Be assured that there’s
no downside related to increasing the subs’ activation sensitivity. When your
external active crossover controller’s low pass outputs (to the subs’ inputs)
cease sending a source signal (for the specified time lapse) to the subs, they’ll
automatically revert to their dormant sleep mode, exactly as intended. The only
instance in which this might not happen is if your crossover controller
suddenly became intolerably noisy—with noise so annoying that you’d be fully
absorbed with that fix before noting that the subs didn’t go to sleep.

†It’s only natural that those who own big
full-range floor-standing speakers would assume that the internal high level
crossovers buried inside their costly purchase are both optimum and accurate.
Regardless, their faith is likely misplaced. Accuracy is certain to be deficient
in the case of passive networks that have accumulated appreciable use because
passive high level crossover components drift. High level operation = high
level stress. (Refer paper headed “On Crossing Over,” at https://classicalcandor.blogspot.com/2020/01/on-crossing-over.html.)

BG (April 2021)

On Rational Selection--Part II…

By Bryan Geyer

In Part I, I listed the most important specifications that
should be reviewed when selecting an appropriate power amplifier. These truly
critical parameters included…

            …size and
appearance.

            …input
impedance (Zin).

            …output
impedance (Zout).

            …power
output capability.

            …voltage
gain; i.e., input sensitivity.

Now let’s look at some other specs that merit attention.
These aren’t quite so vital as the essential considerations that were listed in
Part I, where appropriate compatibility was the main objective. Instead, these
specs reflect basic quality-related issues, such as…

SIGNAL-TO-NOISE (s/n) RATIO: Freedom from hum will be
highly dependent on power supply design and grounding issues. Freedom from noise
will generally trace to circuit design and component selection variables. It’s
desirable to exhibit a wide spread (e.g., a difference of 100dB or more)
between the value of a given output signal (the modern reference is 1Vrms) and
the residual detected when there’s no input signal (input shorted). This
represents the amplifier’s innate signal-to-noise (s/n) ratio. It’s commonly measured
through a filter (it’s “A-weighted”) to emphasize audible frequencies
rather than ambient hum or response beyond the audible spectrum. If the consequent noise reading is 10µVrms, the
related s/n would be -100dB relative to a 1Vrms reference. A fine quality solid-state
power amplifier of current design will meet -110dB (re 1Vrms) s/n ratio. A 90dB
s/n ratio is certainly not state-of-the-art, but it’s relatively acceptable. A
s/n ratio that dips to -80dB (0.1mVrms re. 1Vrms) means that you’ll start to
hear some annoying background hiss from your loudspeakers, dependent on their
efficiency. Of course, all vacuum tube power amplifiers produce poor
signal-to-noise ratios—it’s an inherent limitation.

QUIESCENT DC OFFSET VOLTAGE: Well, it’s just nuts to
neglect checking your power amplifier for DC offset. It’s easily measured with
almost any DC voltmeter, and it’s vital that offset be minimized. Do it! Check
this column for background info.: https://classicalcandor.blogspot.com/2019/10/on-power-amplifier-dc-offset.html

FREQUENCY RESPONSE, DISTORTION, & DAMPING FACTOR:
These specs were once of vital concern in expressing the efficacy of a power
amplifier. That’s no longer the case today because virtually every solid-state
power amplifier exhibits near-perfection with respect to its innate frequency
response and distortion performance. Ditto for damping factor, as that
parameter is directly related to a solid-state amplifier’s ultra-low output
impedance; refer Part I of this paper. As a consequence, you can safely skip
these three specifications when ranking the merits of solid-state power
amplifiers. Any divergence will be too small to justify analysis. Conversely,
there are operating characteristics that you should research, such as…

INPUT OPTIONS: If it’s your intent to apply balanced
interconnects, make certain that the required XLR sockets are provided. I don’t
personally recommend the use of XLR balanced interconnects in a normal home
stereo installation (refer “On Noise, Coax, and Control” at https://classicalcandor.blogspot.com/2020/08/on-noise-coax-and-control.html);
however, you might want that option. Balanced in/out connections are of great
benefit when operating in noisy environs, but typically present no measurable
advantage in benign home environs. XLR plugs and sockets derive from an archaic
vintage (see https://classicalcandor.blogspot.com/2019/10/on-equipment-interface-options.html),
so they’re grossly oversized and generally awkward to accommodate.

Most modern power amplifiers now offer both XLR (balanced)
and RCA-type (unbalanced) inputs, although some older units might lack the XLR
option. Confirm (view back panel photo) that you’ll get what you want. To the
best of my knowledge, there’s just one power amplifier on the commercial market
that provides XLR balanced stereo inputs but NO unbalanced (RCA-type) stereo
inputs, and that’s the Benchmark AHB2. They offer short RCA-to-XLR adapter
cables to accommodate users that require unbalanced input compatibility.

POWER LINE PROVISIONS: Verify that any power amplifier of
interest will be compatible with the power line provisions available at the
site where the amplifier is to be installed. This implies more than merely
confirming that the AC supply voltage and power line frequency are compatible—it
should also encompass the AC current drain (AC line load) compatibility. Refer
“On Assuring Adequate AC Power” at https://classicalcandor.blogspot.com/2020/05/audio-tech-talk.html.

TURN-ON and TURN-OFF PROVISIONS: While it’s always
possible to turn your power amplifier on/off manually, via a switch that’s
wired in series with the power supply, there are potentially more convenient
options to consider. Here are some popular automatic control options…

(1)  Turn on/off
via a low voltage (12-15V) DC control signal: This is a popular turn-on option.
It’s commonly offered on many modern power amplifiers and on other peripheral
components.

(2)  Turn on/off
via signal sensing: The amp senses an audio input, then turns on. The turn on
sensitivity setting is generally variable, via a back-panel switch or pot, so
that background noise won’t be sufficient to falsely trigger operation. The off
function is generally based on a time delay; i.e., when no input signal is
detected for a specified period of time (e.g., 5 minutes) the amplifier then
turns off.

In either case, it’s helpful to have a power amplifier
that connects the input signal path only after a momentary (relay-controlled)
sequential delay. That permits the initial DC power-up surge to “settle out”
first, so that there’s no audible turn-on “thump”; i.e, no sound output until
the amplifier’s internal DC power supply has stabilized.

IN THE FUTURE: As you consider these issues, do bear in
mind that the days of a stand-alone stereo power amplifier look limited. The
current design trend is to fully integrate the power amplifier with the
loudspeaker system. Future audio systems will reflect that preference,
especially when listeners learn to appreciate that…

…it’s more accurate to use active—rather than
passive—crossover networks to feed the drivers in a speaker system with their
intended passbands.

…low bass frequencies (those < 60 Hz) can be more
accurately produced by separate self-powered subwoofers than by an integrated
driver that must also handle all of the mid-bass frequencies (to 600 Hz) as
well. The best top quality speaker systems will no longer include multiple
large diameter woofers because we’ve learned that the classic all-in-one-box
approach is an inferior and outmoded way to implement a full spectrum sound
system.

BG (February 2021)