Violectric DHA V590² Pro Headphone Amplifier, Preamp, and DAC - Manual (Page 26)

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Why does PRE-GAIN make sense?
Two extreme examples (with the DHA V590 with +6 dB gain (factor 2), volume control set to full):
1st example:
The (pre-) amplifier provides 8 V output voltage, whereas the headphone requires only 2 V
for 100 dB sound pressure level.
With the volume control fully turned up, the amp would deliver 16 V output at +6 dB gain. Therefore,
the volume control would have to be operated very carefully to avoid hearing damage. Moreover,
any interference at the input should be avoided since it would be "unforgivingly" amplified as well.
With PRE-GAIN, the input level can be reduced by 12 dB (a fourth), with 2 V instead of 8 V input level
as the result. This 2 V is again amplified by 6 dB, then equalling around 4 V. Now the volume control
can be turned over almost the entire range.
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 4 V at +6 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 6 dB or
factor 2, now equalling 16 V. This is more than enough to drive the headphone.
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 a small one,
manufacturers like Noble or Panasonic don't offer these anymore. A current sample of top of the line
pots is the RK27 by ALPS, which is used inside DHA V590 (standard version).
About the sophisticated volume control of DHA V590 PRO
It offers a just normal looking big knob on the front panel. To enable the same touch and feel of
standard solutions we are using a motor driven potentiometer. Due to a friction clutch between
motor and potentiometer, manual and remote operation of the knob at the same time is possible
without the risk of damage (although not useful…).