Here is a snippet from an email from Jonathan Carr (Lyra cartridge designer) about objectives and considerations regarding cartridge loading.  Most of this is old news, I only re-post it here as a convenient synopsis on this most misunderstood topic. 

The interesting point, for me at least, is Jonathon's statement (at the bottom) that since most step-up transformers act as band pass filters, additional loading to tame RF resonant frequencies is unnecessary.  I have often believed this based on my own experiments, but have not seen anyone else share this result.

Hi:

The proper loading value is difficult to say without knowing your
system, as it is partly a preamp and ultrasonic RF issue as well as
one that involves the cartridge and audible frequencies. Some
cartridges have frequency abberations within the audible band, and
may requre loading to achieve a flat energy response. However, the
Lyra cartridges aren't made like this, and don't need to depend on
loading for good frequency response within the audible range. In
other words, changing the input loading won't have much impact on the
frequency response of a Lyra.

OTOH, the inductance of a cartridge can react with cable capacitances
and cause a sizeable resonance, but with high-impedance loading (like
47k) and MC cartridges, the center frequency of that resonance is far
above the audible range - think 1MHz or so. If the phono stage or
preamp doesn't have a problem with that (ie., it is either linear at
MHz frequencies, or bandwidth limited at the input so that RF energy
can't come in), the RF energy will stay RF and remain inaudible. But
if the phono stage has some response at RF frequencies but is
non-linear at those frequencies, sum-and-difference modulation
between the RF energy and the audio signal will occur, with the
result that you may get distortion products at audible frequencies
that are not hamonically related to the music signal, and are
therefore quite objectionable to the ears.

The Lyra-Connoisseur phono stages have 47kohm loading and MHz
response (although there is some input filtering to remove CB, FM
signals et al), but since they remain linear at these frequencies,
they are not particularly affected by electrical resonances between
the cartridge inductance and cable capacitance. But for some phono
stages, 1kohm works better. And with other phono stages, I've had to
go as low as 100ohms for subjectively decent results.

Also note that environmental RF can come on top of the electrical
resonance caused by the cartridge-cable-input network, and make the
phono stage's life that much more difficult - and the RF environment
for each audio system is different. So the choice of loading is a
case-by-case scenario.

In general, however, I prefer under-damping (higher resistance
values) to overdamping. A lot of audiophiles seem to like a warm,
super-smooth smooth, and if this describes you, over-damping may be
what you want. But for my tastes, over-damping, while inoffensive,
also tends to be bland and uninvolving.

Electrically, you can obtain a better response by using a capacitor
as well as resistor in the input impedance network, but due to the
low source impedance of many MC cartridges (including the Lyras),
small capacitor values (of the type that you would use for MMs) will
not have much effect.

Also note that you want good phase response as well as good audible
response, so the net bandwidth should extend considerably farther
than the audible range per se, while overdamping will accomplish the
opposite.

I don't have the Argo inductance at hand, but I think it is about 8uH.

The Dorian should be around 12.5uH.

The Helikon is a little higher, about 8.8uH.

The Titan is likewise about 8.8uH.

The SL versions will have around half the inductance of the standard
models.

regards, jonathan carr

PS. The best way of loading would probably be to reproduce a square
wave with the cartridge and adjust the loading so that the square
wave looks the best on a scope.

PS. A transformer acts as a band-pass filter, and with the amount of
transformer inductance needed for good bass performance, in most
cases you won't need to worry about the RF issues that I alluded to
in my previous post. Autoformers usually have greater bandwidth
extension than transformers, but in this case probably still not
enough to get you into hot water.

 ***The proper loading value is difficult to say without knowing your system, as it is partly a preamp and ultrasonic RF issue as well as one that involves the cartridge and audible frequencies. Some cartridges have frequency abberations within the audible band, and may requre loading to achieve a flat energy response. 

OK, this is a well know thing but the selection of the words makes me a little suspicious...

 ***However, the Lyra cartridges aren't made like this, and don't need to depend on loading for good frequency response within the audible range. In other words, changing the input loading won't have much impact on the frequency response of a Lyra. 

Here we go! What an accomplishment! I wonder if the Lyra cartridges sound so gray and so boring because of this “accomplishment” or there is any other reasons.

 ***OTOH, the inductance of a cartridge can react with cable capacitances and cause a sizeable resonance, but with high-impedance loading (like 47k) and MC cartridges, the center frequency of that resonance is far above the audible range - think 1MHz or so. If the phono stage or preamp doesn't have a problem with that (ie., it is either linear at MHz frequencies, or bandwidth limited at the input so that RF energy can't come in), the RF energy will stay RF and remain inaudible. But if the phono stage has some response at RF frequencies but is non-linear at those frequencies, sum-and-difference modulation between the RF energy and the audio signal will occur, with the result that you may get distortion products at audible frequencies that are not hamonically related to the music signal, and are therefore quite objectionable to the ears. 

Once again: it is a correct prostration of facts but why he would imply the high inductance MM cartridges buy presenting those facts.

 ***The Lyra-Connoisseur phono stages have 47kohm loading and MHz response (although there is some input filtering to remove CB, FM signals et al), but since they remain linear at these frequencies, they are not particularly affected by electrical resonances between the cartridge inductance and cable capacitance. But for some phono stages, 1kohm works better. And with other phono stages, I've had to go as low as 100ohms for subjectively decent results. 

I knew that the reference to his high gain Connoisseur phono stages is coming. Would be his response is just buttering of Reality in order to convince himself and others that Connoisseur is the only preamp that “does it right”? I wonder how the Connoisseur own SS hardness affects a listener perception of “correct loading”?

 ***Also note that environmental RF can come on top of the electrical resonance caused by the cartridge-cable-input network, and make the phono stage's life that much more difficult - and the RF environment for each audio system is different. So the choice of loading is a case-by-case scenario. 

Certainly it is but still I do not know where he is going.

 ***In general, however, I prefer under-damping (higher resistance values) to overdamping. A lot of audiophiles seem to like a warm, super-smooth smooth, and if this describes you, over-damping may be what you want. But for my tastes, over-damping, while inoffensive, also tends to be bland and uninvolving. 

Yes, and now. What Jonathan forgets to mention that using the phrases “under-damping” and “overdamping” he implies that there is such a thing as a “correct exact damping”. However, the “correct damping” is unfortunately exist only in a virtual subjective perception and HUGELY depending on very- very- very many others, primary masking factors.

 ***Electrically, you can obtain a better response by using a capacitor as well as resistor in the input impedance network, but due to the low source impedance of many MC cartridges (including the Lyras), small capacitor values (of the type that you would use for MMs) will not have much effect. 

Sure, this is well know facts….

 ***Also note that you want good phase response as well as good audible response, so the net bandwidth should extend considerably farther than the audible range per se, while overdamping will accomplish the opposite.

OK, now. Why he threatens the poor audiophiles with the fear of “good phase response” and associate the “bad phase response” with the overdamping?

 ***The best way of loading would probably be to reproduce a square wave with the cartridge and adjust the loading so that the square wave looks the best on a scope. 

Probably he is correct, however considering that the loading is very much might be subjectively overwritten by many-many other factors then what would be the purpose of the loading tuning via the scope? I wonder how the square waves test would differentiate itself if for instance the VTA is off for a fraction of degree or is the primary resonance of the arm is overdumped?

  ***A transformer acts as a band-pass filter, and with the amount of transformer inductance needed for good bass performance, in most cases you won't need to worry about the RF issues that I alluded to in my previous post. Autoformers usually have greater bandwidth extension than transformers, but in this case probably still not enough to get you into hot water. 

Sure, for a guy who manufactures the 88dB active gain phonostage it would be understandable to consider a transformer acts as a band-pass filter. In fact his is very much correct but … there are some “howevers”… If Jonathan bring his Connoisseur in my room and raise the input impedance of his phonostage then I will be very glad to connect it to Expressive Technologies SU2 or SU1 transformer and to demonstrate to him how this “band-pass filter” will VERY substantially increase the low and high frequency response of his phonocorrector (not to mention the it will bust the dynamic range inhumanly!) It would be fun to listen the further Jonathan’s theories about the band-pass filtering ability of the transformers after that (even if I do agree that a transformer ordinary do act as a band-pass filter)

***Here we go! What an accomplishment! I wonder if the Lyra cartridges sound so gray and so boring because of this “accomplishment” or there is any other reasons.

***I knew that the reference to his high gain Connoisseur phono stages is coming.

Self-promotion isn't too surprising here.  These are his babies.

***Yes, and now. What Jonathan forgets to mention that using the phrases “under-damping” and “overdamping” he implies that there is such a thing as a “correct exact damping”. However, the “correct damping” is unfortunately exist only in a virtual subjective perception and HUGELY depending on very- very- very many others, primary masking factors.

Now we are getting nearer to the point.  It strikes me as funny that some vinyl people calculate cartridge loading to a precision of 0.1 ohms.

***(even if I do agree that a transformer ordinary do act as a band-pass filter)

Look, vinyl people hold very strong opinions about having the precise cartridge loading for their cartridge.  Some claim +/- 1 or 2 ohms is critical.  But if the objective of loading is to tame RF resonances, and step-up transformers filter these frequencies, then what are the 0.1 ohm people talking about?  I believe they make changes because they think it sounds better.  But this has nothing to do with the intended objective of taming RF peaking. 

First of all I disagree that the objective of loading is to tame RF resonances. The tame RF resonances is what is the most easily observable. I personally never care about RF resonances while I chase loading but only about the LF.

Secondary, I do not believe in the phrase: “vinyl people hold very strong opinions”. I know those “vinyl people” and I do not respect or value the “wisdom” they express. For instance here is a listening room of Myles Astor, the person who loved to review $10.000 cartridges, claming that his tonearm's dumping is sensitive to the Moon’s gravitation and his woofers detect the earthquakes across the Globe.

 

Those people do tell to each other the stories about the 0.1-Ohm cartridge loading, setting the VTF to .001g and the benefits to Sound by aligning the phono-cable with the Earth’s magnetic lines. You have to once to stop by in thier listening rooms and to hear what ACTUALY they deal with. When you hear the sound they get in their rooms then you will not have any further doubts.

Rgs,
The Cat

I do not completely agree with everything that Dave imply in this article but all-together it is a very good article. The phase by logging graph is particularly interesting and I did not seen it was published anywhere.

http://www.intactaudio.com/forum/viewtopic.php?t=945