Violectric DHA V226, Руководство пользователя

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User´s Manual DHA V226, November 2021, F. Reim
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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.
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-amp 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 DHA V226 with +2 dB gain (factor
1,25), 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 10 V
output at +2 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
+2 dB, then equalling around 2,5 V. Now the volume control can be
turned over almost the entire range.