I've played around with loading quite a bit (though not on an XV-1S), trying loading on the primary vs. the secondary, various types of load resistors, different SUTs, etc. It's all guesswork in my opinion, and completely system dependent. When I've had different tonearms on the deck using the same cartridge, I've noticed I've had to tinker with loading - sometimes the difference is subtle, sometimes night and day (ahem). One of the better explanations as to why this is the case came a while ago from Jonathan Carr of Lyra in this thread (the pertinent excerpt from it is below):
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1258844370&openusid&zzJcarr&4&5#Jcarr
>>You are very crisp with your technical specifications, however, you openly offer a wide range for cartridge loading (100 Ohms to 47 kOhms). Why such a range?
First, because the loading of a low-impedance MC is not really an issue for the cartridge itself. An MC cartridge is a mechanically-driven electrical generator, and a not-very-efficient one at that. Unlike loudspeaker drivers, the meager efficiency of a low-impedance MC cartridge implies that loading applied in the electrical domain will have relatively little effect in the mechanical domain (which is where you will see effects on aspects like tracking performance and distortion). Also, due to the very low inductance of the signal coils, electrical loading will have practically no effect on any signals in the audible range, and this has other benefits in keeping a relatively flat phase response in the audible domain (a general rule of thumb for good phase response out to 20kHz is that the electrical frequency range should extend to at least 200kHz). This is a completely different situation with high-inductance MMs and MIs, where changing the loading will affect the frequency response in the audible range, and the phase response even more so.
So, if electrical loading doesn't change the behavior of the phono cartridge in the audible frequency range by much, why does the sound change so dramatically? The answer is that the inductance of the cartridge coils will resonate with the capacitance of the tonearm cable (and distributed capacitance of the coil windings) and create a high-frequency spike. The magnitude of this spike can be extremely high, and may give many phono stages outright problems if it isn't damped with loading measures at the phono stage input. I don't have my lab notes at hand, but from memory loading a Delos with 47kohm can result in a 28dB spike at 6~7MHz. Some phono stages will have been designed so that they remain unflustered by this, but many phono stages will not be happy with such brutal treatment, and will not sound good because of this. >>
Hope this is of some use. Happy hunting!
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1258844370&openusid&zzJcarr&4&5#Jcarr
>>You are very crisp with your technical specifications, however, you openly offer a wide range for cartridge loading (100 Ohms to 47 kOhms). Why such a range?
First, because the loading of a low-impedance MC is not really an issue for the cartridge itself. An MC cartridge is a mechanically-driven electrical generator, and a not-very-efficient one at that. Unlike loudspeaker drivers, the meager efficiency of a low-impedance MC cartridge implies that loading applied in the electrical domain will have relatively little effect in the mechanical domain (which is where you will see effects on aspects like tracking performance and distortion). Also, due to the very low inductance of the signal coils, electrical loading will have practically no effect on any signals in the audible range, and this has other benefits in keeping a relatively flat phase response in the audible domain (a general rule of thumb for good phase response out to 20kHz is that the electrical frequency range should extend to at least 200kHz). This is a completely different situation with high-inductance MMs and MIs, where changing the loading will affect the frequency response in the audible range, and the phase response even more so.
So, if electrical loading doesn't change the behavior of the phono cartridge in the audible frequency range by much, why does the sound change so dramatically? The answer is that the inductance of the cartridge coils will resonate with the capacitance of the tonearm cable (and distributed capacitance of the coil windings) and create a high-frequency spike. The magnitude of this spike can be extremely high, and may give many phono stages outright problems if it isn't damped with loading measures at the phono stage input. I don't have my lab notes at hand, but from memory loading a Delos with 47kohm can result in a 28dB spike at 6~7MHz. Some phono stages will have been designed so that they remain unflustered by this, but many phono stages will not be happy with such brutal treatment, and will not sound good because of this. >>
Hope this is of some use. Happy hunting!