Magnetic circuit
Once the mechanical assembly had been perfected the next area to which particular
attention was paid was the magnetic circuit.
From numerous tests carried out on a variety of materials and configurations, it was
established that different types of magnetic materials exert a subtle influence on the
perceived quality of the final sound.
After further extensive research the optimal magnetic circuit was found to be electro
magnetically generated. This, however, requires a separate DC power supply and is
very costly to implement. Therefore, only a cartridge producing the absolute ultimate
in performance could employ such a system… and the IO Limited was born.
Wire Material
Because of the low impedance and very low output of the IO Limited, it is essential
that the minimum number of electrical connections occur along the wire and that the
wire itself is of the highest possible quality. Not surprisingly we chose our custom
made Audio Note (UK) 99.99% pure silver wire, and the coil wire extends all the way
to the output terminals, avoiding all unnecessary connections.
Cantilever, Material and Design
It is on the design and construction of the cantilever that much of the quality of a
cartridge depends. Many materials were investigated, Boron, Beryllium, Sapphire,
Diamond and Titanium and all except Titanium were disregarded in the final analysis,
due to deficiencies in one or more areas.
It is vitally important for the cantilever and stylus assembly to be as rigid as possible
in order to accurately transfer the stylus motion to the coil assembly, without adding
any unwanted vibration as a result of flexing or bending.
The optimum cantilever material here was found to be an extra thick walled, slightly
tapered Titanium tube, the taper being both outside AND inside, since this affords by
far the greatest rigidity.
Another advantage provided by this type of material was the possibility of employing
a longer cantilever, which greatly reduces cantilever excursions. This has three main
benefits: -
1)
It is easier for the stylus to track complex, highly modulated grooves.
2)
The resultant smaller coil movement reduces the nonlinearities in the magnetic
field, so the field will
ʻ
bend
ʼ
less.
3)
Damping can be reduced, as it becomes easier to control stylus movement.
IO LIMITED MOVING COIL CARTRIDGE
