The
B
stands for band width and will be discussed later.
When a source like a MC pickup with it matching resistor is connected to a phono preamplifier`s input the output noise
includes contributions from both the amplifier and the source resistance. There exists an optimum source resistance for any
given amplifier, which will provide the lowest noise factor, or in other words the highest signal-to-noise ratio for any specific
input signal.
Since the source resistance is determined by the pick-up manufacturer, there is only one way left to optimize the overall
noise performance of a phono preamplifier.
The amplifier has to be designed in that way that it matches with these source resistances of the MC pick-ups or at least
come close to this value.
After solving some partial differential equations, it can be shown that the optimum source resistance is
n
n
e
R
i
=
That means for a given amplifier the optimum source resistance can be calculated. Beside the low noise performance, the
amplifier has to match to other requirements as well. For instance the amplifier has to be linear and should not add any
distortion or the bandwidth should be well above the audio bandwidth and so on.
