Violectric HPA V281, User Manual

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difference between the interference contents: (s) – (s) = 0. Thus - in an
ideal situation - all interference on the signal path is eliminated.
Why are discrete signal paths important ?
Twin op-amps are the most common design for operational amplifiers,
i.e. two amplifier circuits are integrated in one device. If left- and right-
channel signals are processed simultaneously by such a device,
interaction between both cannot be excluded. This interaction is
admittedly diminutive, but should be avoided whenever a different
design offers the possibility.
Why are op-amps ideal for low-level signal processing ?
Discrete amplifiers (designed with transistors) are very popular in high-
end audio design also for preamplifier stages. This is often marketed as
an optimization measure, but the partially exorbitant extra expenses are
of course to be paid by the customer. But an op-amp consists of
transistors as well...
Moreover, its structure has the advantage of thermal coupling between
its internal components. Also ageing issues play a much less important
role. Due to the large number of op-amps types offered, it is possible to
pick an optimum type for any specific application.
Why does PRE-GAIN make sense ?
Two extreme examples (with the HPA V281 at +14 dB gain (x 4,5),
volume control set to full):
1st example:
The (pre-) amplifier provides 2V output voltage, whereas the headphone
requires only 2V for 100 dB sound pressure level.
With the control fully turned up, the V281 would deliver 9 V output at
+14 dB gain. Therefore the volume control would have to be operated
very carefully in order 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