Violectric HPA V281 User Manual page 18

Too loud ? Too soft ? The PRE-GAIN method
The V281 is specially designed to drive headphones. Headphones
however can present load impedances from 8 to 2000 ohms and
efficiency ratios from 85 to 115dB per milliwatt. Thus it can be quite
tricky to fulfil all demands, since...
... owners of high-efficiency headphones will rarely set the volume
control higher than 9 o'clock in order to exclude hearing damage, while
... the maximum setting may still be too soft for low-efficiency
headphones, but
... all users expect highest quality at lowest noise and distortion.
Thus, the circuitry must adapt itself as the headphone won't !
WE CALL THE SOLUTION TO THIS PROBLEM
The alignment between amplifier and headphone is provided by the
preamp stage, which can boost or attenuate the input signal in four
steps of 6dB each. For this purpose, two switching devices are located
on the rear panel for left and right channel individually.
CAUTION !!
The switch settings should be altered under the following conditions
only:
- The unit must be switched OFF
- the "VOLUME" control must be set to minimum
left and right channel settings should ALWAYS be set the same
-
never increase the setting by more than ONE switch per channel
-
If you find your HPA V281's volume could be somewhat softer (in order
to improve volume control range e.g.), push the switch labelled "-6 dB"
(half gain) or "-12 dB" (quarter gain) in upward direction.
If you find your HPA V281 should provide more gain, do so with the
switch labelled "+6 dB" (double gain) or "+12 dB" (quadruple gain).
Ex-factory, all switches are set to their lowest position - i.e. 0 dB or unity
gain - which should be sufficient for most applications.
PRE-GAIN
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