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THE CLOCKWORK WIND-UP ACOUSTIC GRAMOPHONE AND 78RPM SHELLAC DISC ARE
IMPORTANT HISTORICAL PRECURSORS TO OUR CURRENT HI-FI, BUT MAINS ELECTRICITY HAS
PROVIDED ALL THE ENERGY FOR OUR HI-FI SYSTEMS FOR MORE THAN 60 YEARS. HOWEVER,
INCREASING MAINS POLLUTION POSES A REAL THREAT TO OUR HIGH QUALITY MUSIC
REPRODUCTION, AS BEN DUNCAN EXPLAINS.
In the broadest sense, all high-end music
reproduction requires careful management of energy
in its various forms. The energies that need perfect
handling may be wanted or unwanted, may be acoustic,
mechanical, or electrical, including electro-magnetic
fields and electrical currents, and the various wanted
and unwanted relationships and interactions that occur
between these. What is so often overlooked, of course,
is the invisible energy, and the quality of that energy,
that we must bring into the room, to bring the hardware
– and music – into life.
This is nearly always the AC mains supply, because it
is by far the cheapest source, and also requires the least
management effort. Even after recent steep rises in the
cost of UK electricity, making one’s own AC power is
slightly more expensive, noisy, and (in view of generator
exhaust fumes) potentially hazardous. Eco energy is far
more costly, maybe by one hundred times with its high
up-front capital cost and need for storage batteries, and
also a lot more bother to manage.
Avoiding too much power management is important
to listening enjoyment, as too is an operating cost that
is not out of proportion. When endeavouring to create
high quality sound, there are enough other imperfections
to deal with without worrying overmuch about whether
one is using 10 or 100 watts, or whether there has been
enough sunshine to recharge some solar device, since
some gear was accidentally left on. The public AC mains
supply it is then.
ASPECTS OF AC ENERGY
The fact that the AC supply is public is rarely mentioned
or considered. It also has finite impedance, which is
tantamount to saying that the energy available is finite,
and ‘softly’ limited. Consequently, the supply quality can
be affected by a single user drawing more than his/her
notional share; or many users doing likewise to a lesser
extent. There are few restrictions on, and no real policing
of, what any user plugs into the supply: how much load
is placed on it (so long as the supplier can be paid and
the main fuse doesn’t blow); when that load is on, when
it is off, and how often any loading is repeated. It follows
that use of the public supply for something as sensitive to
power quality as music reproducing equipment, is akin to
using the equally public roads. Depending on both skill
in social timing and pure luck, you may encounter miles
of empty, smooth highway, or the congestion of traffic
capacity overload.
The qualities of AC energy are vastly more
complicated, than someone with basic electrical
knowledge imagines. Compared to audio’s wide span of
levels and signal frequencies, electrical power engineering
appears straightforward enough, with apparently just
one frequency and a few voltages. But, the intricacies are
immense, especially when abusive loads designed and sold
by idiots are factored in.
An example is the TV set. Makers have known full
well and for many years that TV sets have represented
a dominant load on the electricity system in residential
areas, and at certain times of day. An eight year old
can figure this out. Yet most makers have persisted in
making cheapskate products that have, for the sake of
saving costs, used a crude form of switching supply,
since Ferguson first did so around 1966. The size of the
pulsed current draw may not be any greater than that of
a largish hi-fi, but there are ten or a hundred times more
TVs in a given neighbourhood, and the mass operation
of TV sets has long tended to be focused on particular
sectors of day. The overall effect has, in general, seen the
harmonic pollution of the supply rising as industrial
& commercial pollution falls away during the late
afternoon/early evening, then peaking at the main TV
watching times, and fading away again around midnight.
At which time many hi-fi listeners find that they get
better sound. TV manufacturers have not thought
through the consequences of actions they know will be
substantial, and since TV sets are no longer made in the
UK, any opportunity to create better standards for the
hi-fi industry is lost.
A basic quality of the public supply is a voltage
that would, if pure, reach a peak of 339 volts for the
everyday RMS value of 240V. This power-equivalent
RMS value is, however, generally maintained to a fair
standard in UK, largely staying within a few percent
either side of 240V (the supposed change to 230V is
wholly illusory Euro-speak). While the supply level is
monitored and automatically regulated at intermediate
11kV/33kV electricity substations that occur every
12 miles or so, we need to understand that the endusers’
supply fluctuates to a mild extent with virtually
every appliance that’s turned on and off. The effect is
that the supply voltage is never constant. Those who
measure their supply once and then claim “it’s 230V”
are mistaken. A supply can be averagely centred on
240V, but the continuous deviations can be sonically
important; they are unpredictable as to timing, duration
and magnitude. Furthermore, all hi-fi, and much other
equipment, relies not on the RMS but on the peak
value, for which suppliers are wholly non-cognisant.
Degraded sound may be caused by the peak value being
way low or high, while the RMS value remains relatively
within limits. I term this ‘bad crest factor’.
THE SUPPLIER
The supplier or network owner (in the UK at least) has
to be mindful in law of mains quality, but only to a
limited extent. And only complainants used to dealing
with large organisations will get far with rectification.
Expect one or more years of letter writing. If engineers
actually owned the privatised distribution companies,
AC supply quality might be taken more seriously, since
their capital equipment is made less efficient or can even
be damaged, by a surfeit of ‘bad loads’. Common such
loads in urban areas are the hundreds of idiot-designed
low voltage halogen lamps, the problem being caused by
saturation in the associated low grade, penny-pinching
E-I core transformers, often one per lamp. Along with
the halogen content and the UV rays, a less ecological
form of lighting (and potential way to start a house fire)
would be hard to contrive. Meanwhile, the circulating
‘triplen’ (third, alias 150Hz) harmonics generated by
hundreds of stressed little transformers adds distortions
to the supply that are largely un-filterable. The cheap
switch-mode regulators now frequently substituted for
those toroids are even worse.
In your home, halogens and low energy fluorescent
lamps are OK if you can switch them off when listening.
The ones to worry about are those you can’t switch
off in your neighbours’ houses. The Government’s
technologically illiterate phasing out of ‘high energy’
incandescent lamps won’t help sonic quality: traditional
incandescent lamps actually help power quality by being
virtually pure resistive loads.
Sonic problems can be caused by excess AC voltage.
Equipment with under-rated toroidal transformers
saturate suddenly above a certain voltage, creating a
mechanical buzz when this happens. E-I transformers
saturate gradually, so adding some distortion at all times,
like valve amplifiers. Well designed, suitably over-rated
toroidal transformers avoid adding any distortion under
all conditions. Rather like a good high-feedback amplifier,
you must have a large enough rating so you never reach
‘clipping’. This approach applies in both equipment
transformers and passive power conditioners (both
isolation and transductor devices), and even with active
power conditioners, where too small an E-I or toroid may
distort the AC to any hi-fi gear that’s not run through a
Power Conditioner (PC).
As no supply has infinite capacity, and as the end-user
voltage isn’t regulated, it’s obvious that a public supply
voltage will vary randomly all the time, with the bigger
changes down to mass human behaviour patterns. And
it’s most likely to be at its high end when the system is
lightly loaded, ie the small hours of the night which are
often favoured for serious listening.
To look for either excess voltage, or correlations
between extremes and sonic degradations, the user must
take many readings at regular intervals and through whole
weeks. Previous articles, reprinted as AQMS[1], give
full details. Plug-in electrical usage measuring units are
now available at low cost, and these will display voltage
without the hazards of using a multimeter.
The supplier can be required to reduce the voltage if
it’s provably and regularly above the legal limits, but that
may be ethically problematic by causing users further
away from the substation the opposite problem of too
low a voltage – particularly as the voltage can also only
be adjusted in crude steps of typically 10V. A voltage that
varies widely but stays within the legal limits probably
doesn’t cause many problems, but it can with poor
designs. Since the 1970s, equipment of my own design
has been tested to operate correctly and indefinitely at
below 200V and as high as 265V. Other equipment, even
of otherwise good design, can give bad sound if the mains
is just a tad low, because almost no one tests the finished
product in this way.
"Θαυμάζω την κομψότητα της μεθόδου σας. Πρέπει να είναι ωραίο να καλπάζεις με το άλογο των αληθινών Μαθηματικών, ενώ εμείς οι υπόλοιποι αγκομαχάμε στον ποδαρόδρομο" - ο Άλμπερτ Άινσταϊν στον Τούλλιο Λέβι-Τσίβιτα