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In the Forum: Analog Playback
In the Thread: Taking the mystery out of cartridge loading
Post Subject: Taking the mystery out of cartridge loadingPosted by skushino on: 2/26/2005
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.
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
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
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
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.
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