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instabilities. A buffer amplifier "reconditions" the signal and makes it
compatible with other devices due to its low-impedance output.
The HPA V200 is DC-coupled, i.e. it can transduce DC voltage as well.
For good measure, a low-cut filter can be inserted by setting the
corresponding jumpers. After input buffering, the signals are forwarded
to a simple 6dB-per-octave filter stage which can be set to two
characteristics: AC (12 Hz), or DC (0 Hz).
Why does frequency bandwidth limiting make sense ?
In signal processing, sound is represented by AC voltages. Sound is
audible - for young people - from about 20 to 20000 Hz. The elder the
listener, the less he will hear high frequencies in particular.
In order to transmit these frequencies at optimum quality, the frequency
response of an amplifier should be as wide and as "flat" as possible. At
the low end of the scale, this limit is represented by DC, as there is no
frequency lower than zero. In upward direction, the limit can be set to
practically any frequency, but the higher, the more susceptible the device
becomes concerning electro-magnetic interference. This is not audible in
the first place, but may interfere with the useful signal and then become
evident. Therefore, unrestricted frequency response attests
thoughtlessness rather than remarkable engineering skill.
Here comes the volume pot.
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 multitap 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 V200.
