Violectric DHA V590² Pro Headphone Amplifier, Preamp, and DAC - Manual (Page 25)

25
Things to know …
Why makes it sense to make such huge efforts?
A headphone amplifier is a device designed to condition audio signals with regard to the very
specific requirements of headphones. This does not sound too spectacular at the first glance and can
be achieved relatively easy. As with many things however, the devil is in the details and much more
effort is required to design one amplifier for all current headphone models.
Headphones per se are quite diverse, and there are two essential parameters:
Impedance and Sensitivity.
In general, headphones with higher impedance can be regarded as less sensitive than headphones
with low impedance (which is not generally true, but in the majority of cases). The sensitivity of
headphones is usually stated in dB SPL (sound pressure level) per Milliwatt.
Extremes in this sense are the AKG K1000 with 74dB/mW on the one hand, and the Sennheiser
HD25 with108 dB/mW on the other hand: The K1000 requires 2500 times the power to achieve the
same sound pressure as the HD25.
There is also the fact that headphones with high impedance usually require much higher voltage to
achieve high loudness. Thus, the amplifier
must be designed with high internal supply voltages.
Which advantages do balanced signals offer?
In contrast to unbalanced signals, balanced signals are carried by two wires (plus ground/shield). In
the transmitting device, a balanced signal is created by generating an inverted signal (180
0 phase
shifted). The "hot" wire carries the original signal (a), the "cold" wire carries the inverted signal (-a).
In the
receiving
device, the
balanced
signal is
processed by
a differential
amplifier
which detects
the difference
between both:
(a) – (-a) = 2a.
On its way between devices, the useful signal can be affected by interference (s). Interferences
however are in phase on both wires and fed to the differential amplifier as well. Again, the amplifier
detects the difference between the interference contents: (s) – (s) = 0.
Thus - in an ideal situation - all interference on the signal path is eliminated.
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.