Violectric PPA V600, Руководство пользователя

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The PPA V600 offers both balanced and unbalanced inputs.
What's the advantage of a balanced signal ?
In contrast to unbalanced signals, balanced signals are transmitted via two wires
plus ground connection. A balanced signal is accomplished by inverting the
original source signal at unaltered level. One wire carries the original, unaltered
signal (a), the second wire the inverted signal (-a).
At the receiving input, the signal is fed to a differential amplifier which 'sees' the
difference between a and -a only, at a resulting level of 2*a.
On a signal path between devices, interferences (s) may try to disturb the signal
by entering the connecting line, but being in-phase with respect to both signal
wires. The differential input again sees the difference between interferences on
both wires only. Thus - after the rule (s) - (s) = 0 - they are eliminated almost
completely.
The PPA V600 uses instrumentation amplifiers.
Why did we choose instrumentation amplifiers ?
Like mentioned earlier, the balanced signals are fed to special instrumentation
amplifiers with differential inputs, which were originally intended for the use with
microphones. However, the difference between dynamic microphones and
pickup systems isn't as big as one might assume: By means of wire coils and
magnetism, they both deliver very low signal voltage at quite similar impedance.
During design, we discovered that this breed of instrumentation amplifiers is
ideally suited for turntable pickups as well.
The PPA V600 has a gain control on the front panel
Why is an easily accessible gain control useful ?
A further advantage of instrumentation amplifiers is that gain can be adjusted by
rather simple measures. Furthermore, gain control can be achieved without any
significant change in bandwidth, as faced with (multi-stage) operational
amplifiers. Thus, bandwidth still exceeds 200kHz at a gain setting of remarkable
60dB, equalling a level ratio of 1:1000 !
By means of the front gain controls, the PPA V600 can easily be adjusted even
for less known pickup models without hassle. Adjustment is provided for both
channels individually, in order not to impair crosstalk rejection. At the same time,
precision resistors ensure perfect stereo matching at 0.25 dB tolerance.
The PPA V600 offers balance control on the front panel
Why is easily accessible balance control important ?