Violectric DHA V226, User Manual

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User´s Manual DHA V226, November 2021, F. Reim
2nd example:
The (pre-) amplifier provides 2 V, whereas the headphone requires 10 V
to release 100 dB of sound pressure.
With the volume control fully clockwise, the amp would provide around
2,5 V at +2 dB gain only – much too low for the headphone. By means of
PRE-GAIN, input level can be boosted by 12 dB (four-fold), resulting in
effective 8 V input voltage instead of 2 V. These are again multiplied by
+2 dB or factor 1,25, now equalling 10 V. This is exactly what the
headphones demand.
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.
Why a good volume attenuator is essential?
“Normal” devices do have a volume potentiometer which is a
mechanical control element, it can be obtained on the market at any low
price. Meanwhile it is often replaced by electronic circuitry, often
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