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While the loading of moving magnet cartridges is rather straight forward, the loading
of moving coil cartridges is at best a very inexact science. Specifi c requirements for
loading moving coil devices should be taken (and offered) very lightly.
The XP-27 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-27 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-27 is suffi ciently revealing such that the resistance and reactance of
that wire should be accounted for in choosing loading values in the XP-27. As long as
you derive your fi nal 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 defi nition 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. Specifi cally in selecting a cartridge load, we will
be listening for a compromise loading which sounds best across the whole audio
spectrum and specifi cally not that loading which optimizes one cut on one LP.
The front panel controls of the XP-27 load each channel of the phono-cartridge
independently through closely matched devices to preserve the best possible spatial
elements of recordings. The XP-27 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 fi gures 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-27 cartridge loading. Load and input changes
made to the XP-27 have a small but non-zero possibility of sending pulses to your pre-
amplifi er that could damage loudspeakers provided the volume of the pre-amplifi er
is set suffi ciently 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-27 electronics
a couple of minutes to settle in and listen to the system critically for some time (10
minutes to 1 hour) using various musical selections that you are familiar with.
Once again reduce the gain on your preamp and select the next lowest resistive
loading value (50 ohms) from the XP-27 front panel. Once again give the electronics