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frequency response attests thoughtlessness rather than remarkable engineering
skill.
Why is a good volume pot essential ?
A volume potentiometer is a mechanical control element, which can be obtained
on the market at any low price. Meanwhile it is often replaced by electronic
circuitry, exhibiting essential disadvantages concerning dynamic range, noise
and distortion.
Conductive-plastic resistive tracks, high-quality multi-tap wipers and separated
chambers for the individual sections are highly desirable for sophisticated
applications, and high quality is inevitable to ensure trouble-free operation for
years. Since the market for really good pots is a small one, manufacturers like
Noble or Panasonic don't offer these any more. A current sample of top of the
line pots is the RK27 by ALPS, which is also used in your HPA V280.
Why is a low output impedance essential ?
When actuated, electro-dynamic systems respond with a counterforce. When
the voice coil of a headphone has been displaced by the signal, an (error-)
current will be induced when it swings back to its initial position. This current
must be suppressed as far as possible, which is effected best if the amplifier's
output impedance is the lowest possible. The damping factor describes nothing
but the ratio between output impedance of an amplifier and a given load.
Since there is no known technical specification, we define the load (voice coil
impedance) as 50 ohms. With V280 having an output impedance of <0.2 ohms
this results in a damping factor 250.
Why are high supply voltages essential ?
A headphone doesn't really require high power, but from the equation
P = U2 / R we can see that the square of the supply voltage determines the
power into a given load resistance. The higher the headphone's impedance, the
more voltage will be needed. But this deals with the achievable loudness to a
limited extent only: Technically spoken, music lives on fast transients which put
high demands on signal processing. And thus a fast transient can easily push an
average amplifier with +/-15 volts supply to its limits (90 % of all headphone
amps in the market are operated with these or even lower supply voltages). Due
to the high supply voltage of V280 you will benefit from more than doubled
output voltage swing capability.
