Violectric HPA V90, User Manual

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Things to know …
The HPA V90 offers unbalanced inputs. The input signals are fed to
buffer amplifiers - for left and right channel separately - which also
provide the PRE-GAIN setting.
Your HPA V90 also offers an active feed-throu with dedicated buffering
amplifiers. This helps to use the input signals for further purposes.
Why does an active feed-through make sense ?
Each electronic device presents input impedance as well as input
capacitance. If several devices would be coupled passively - e.g. with "Y"
adapters - the resulting input parameters could provoke malfunction and
instabilities. A buffer amplifier "reconditions" the signal and makes it
compatible with other devices due to its low-impedance output.
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
tranistors 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.