7
XP-25 Owner’s Manual
The XP-25 is not typical and I encourage you to think separately
from the cartridge manufacturer and choose your resistive loadings
accordingly.
As for example with the very lowest output cartridges, the cartridge
maker likely anticipated a transformer being used as the initial
stage of gain, the XP-25 with its active elements is a very different
proposition from a transformer as seen by the cartridge. This
fundamental difference of circuit topology can affect loading
preferences.
As an added complexity; part of the cartridge loading is always
provided by the lead-in wiring. The XP-25 is sufficiently revealing
such that the resistance and reactance of that wire should be
accounted for in choosing loading values in the XP-25. As long as
you derive your final setting empirically through careful listening you
may ignore these wire effects; however your cartridge will not.
An improperly loaded cartridge will suffer every unwanted sonic
anomaly, ranging from lack of definition and bass to a very strident
and screechy high end.
Cartridge loading is a compromise between what works best for
the cartridge and what sounds best for the listener. Specifically in
selecting a cartridge load, we will be listening for a compromise
loading which sounds best across the whole audio spectrum and
specifically not that loading which optimizes one cut on one LP.
The front panel controls of the XP-25 load each channel of the
phono-cartridge independently through closely to preserve the best
possible spatial elements of recordings. The XP-25 is a dual mono
design, which minimizes cross talk between channels. The loading
resistors and capacitors are isolated from the front panel switches to
provide the best possible signal to noise figures possible.
I suggest you start with the following for moving coil cartridges:
Always, ALWAYS reduce the volume or mute the output of your
preamp before making any adjustments of the XP-25 cartridge
loading. Load and input changes made to the XP-25 have a small
but non-zero possibility of sending pulses to your pre-amplifier that
could damage loudspeakers provided the volume of the pre-amplifier
is set sufficiently high. Damage to your equipment is highly unlikely
but in light of the effort and expense your equipment represents we
believe that caution however un-necessary is warranted.
Start by selecting an initial resistive load of 100 ohms. Give the
XP-25 electronics a couple of minutes to settle in and listen to the
