My two cents about MC cartridge loading:
A moving coil cartridge is an electromagnetic generator and, thus, obeys the laws of electromagnetic induction. Electromagnetic induction is the production of voltage across a conductor situated in a changing magnetic field, or conversely a conductor moving through a stationary magnetic field.
Faraday found that the electromotive force (EMF) produced around a closed path is proportional to the rate of change of the magnetic flux through any surface bounded by that path. In practice, this means that an electrical current will be induced in any closed circuit when the magnetic flux through a surface bounded by the conductor changes. This applies whether the field itself changes in strength or the conductor is moved through it (as is the case in a moving coil cartridge).
In other words, the EMF generated by Faraday's law of induction due to relative movement of a coil and a magnetic field is the phenomenon underlying a moving coil cartridge. When a coil is moved relative to a permanent magnet, an electromotive force is created. If the terminals of the coil are not connected, the EMF appears as a voltage across the terminals. If the terminals of the coil are connected through an electrical load Rload, a current will flow; if Rload=0, the maximal current flows, limited by the internal resistance of the coil windings.
A conventional MC preamplifier is a voltage amplifier with a predetermined (mostly adjustable) input impedance. A cartridge connected to a conventional MC preamplifier sees the input impedance of the preamp as load Rload. The current flowing through Rload generates a voltage drop across Rload which, in turn, is the input voltage fed to the preamplifier and to be amplified.
Two facts need to be pointed out:
(1) As the load is in series with the internal resistance of the moving coil cartridge, a voltage divider is formed with the result that only a portion of the output voltage of the MC cartridge is available for further amplification. Generally, the higher the internal resistance of the cartridge and the lower the load, the less input voltage is available for the preamplifier.
(2) Since it is the voltage across the load resistor that is amplified by a conventional MC preamplifier, the electrical and physical characteristics of the load resistor have a significant influence on the sound. Nobody will deny that differences do exist between real life resistors; thus, it is crucial to use only the very highest quality of resistor as a load for the MC cartridge. But the consumer sometimes has no influence on the quality of the resistor that is used in a particular preamplifier as load resistor, and often, for reasons of economy, not the very best resistors are used. The result is that you listen, at least to some extent, to the sound of the resistor in addition to the signal produced by the cartridge.
There are as many opinions about correct cartridge loading as there are cartridge users around. When using a CMC-Pre, it is common practice to select a load in the region of a few tens of ohms up to 47k or 100k. Since the range recommended by cartridge manufacturers is so broad, the task of selecting the correct load is still not easy.
In view of the physical basics discussed above, it would make more sense to load the cartridge with a high value, i.e. 1kO or above to have an output voltage as high as possible. However, many consumers seem to believe that a considerably lower value is more favorable, particularly in a system having a tendency towards excessive brightness or upper frequency distortion.
The many discussions about correct loading boil down to the fact that the cartridge load resistor is used as tone control or equalizer to compensate for blemishes in the rest of the reproduction chain. A correctly designed, inherently neutral MC cartridge, properly integrated in a neutral reproduction chain, should not need a low value load.
Any comment?
