Moving Coil Cartridges
The Audio Note Io Type Cartridges
As early as in 1978, Mr. Kondo of The Audio Note Company, Japan, introduced his Io cartridge design. The revolutionary nature of the design runs contrary to most accepted design criteria, now, as they did then. The result is a small range of moving coil cartridges, which are second to none in dynamic range, tonal balance, separation, timbral reproduction, and lack of colouration and surface noise.
The cartridge designs do not lend themselves to mass production and as a result are not in-expensive, they require a tonearm of very substantial rigidity, and must be combined with a matching transformer, in order to achieve the best possible linearity and dynamic signal transfer without which it seems pointless to own cartridges of this quality.
All the above make the cartridges relatively costly to acquire and use correctly, but the results are so illustrious and their music making so fine that Audio Note have never found selling them a problem, generally they have been very scarce and hard to find. An annual Production of about 40 - 50 pieces speaks for itself. This has now changed, as of July 1990, the license for making the cartridges was transferred to The Audio Note Co. (UK) Ltd., and after substantial investment in tooling, both for cantilever and body parts, as well as in measurement equipment, the first IoIIv made in the UK was ready in April 1991.
The following paragraphs outline the distinctive design features of the IoIIv, but also apply to the IoIv and the IoLtd.
The basic design criteria can be described as follows:
Mechanical integrity of body.
Magnetic circuit and magnet choice.
Wire material and quality.
Cantilever material, shape and length.
As a basis for the designs the moving coil principle was chosen, as it offers greater linearity in terms of electrical output from the mechanical movements of the stylus.
To ensure that the stored information on the disc is precisely recovered it is essential that the mechanical movement of the stylus is accurately translated into an electrical signal. Any extraneous excitations arising as a result of vibrations in the cartridge housing must be eliminated.
Therefore in the design of the Audio Note cartridges very considerable attention has been paid to the rigidity and structural strength of the body, and to ensuring that the adopted mechanical construction stores the absolute minimum of resonant energy, which will degrade the signal derived from the disc being played.
To adequately achieve this level of mechanical integrity, all aspects of the body design was considered, to minimize standing waves and eliminate any resonating air pockets within the cartridge assembly.
Mechanical integrity of the cartridge body is an aspect of cartridge design that has never been adequately dealt with and as a result all other cartridges suffer greatly from colourations derived from energy stored in their body assemblies.
The benefits of getting the mechanical assembly right would be lost if the complete assembly could not be rigidly mounted to the headshell, hence the incorporation of the largest possible surface mounting area and the provision of up to six (6!) bolts to secure the cartridge to the headshell.
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 by Mr. Kondo, it was established that different types of magnetic materials exert a more or less subtle influence on the perceived quality of the final sound.
After further extensive research the optimal magnetic circuit was found to be electromagnetically generated, this, however, require a separate DC power supply and is very costly in manufacture and therefore only suited for a cartridge of absolute performance, the IoLtd. Second only to the electromagnet in sound quality was the highest grade ALNICO magnet.
In order to develop an extra powerful magnetic circuit Mr. Kondo combined two of these magnets with a pure iron yoke, precision machined in two pieces and subsequently gold plated to prevent corrosion.
This design ensures an accurately focused field of over 2,500Gauss field strength, by far the most powerful of any available cartridge.
The very high strength field enabled Mr. Kondo to significantly reduce the number of turns on the coils, with the twin benefits of reducing distortions and improving sensitivity- In addition a special core material was developed, made from an ultra thin amorphic magnetic material, to ensure increased output without the problems of saturation, so common in other cartridges- The coil arrangement is shielded with a very thin copper shield to exclude extraneous noise and vibration, thereby providing the purest possible electrical output.
Because of the low impedance and very low output of moving coil cartridges, and this design in particular, it is essential that the minimum number of electrical connections occur along the wire and that the wire itself, of the highest possible quality. Not surprisingly Mr. Kondo chose his 99.99% pure silver wire as used in his cables, transformers, etc., and the coil wire extends all the way to the output terminals where it is terminated, this is done to avoid unnecessary connections.
Cantilever Material & 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 in the 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 material here, was found to be an extra thick walled tapered Titanium tube, the taper being both outside AND inside, since this affords by far the greatest rigidity, despite the fact that Boron offers some theoretical advantages, but these cannot be realized in practice, mainly due to current production techniques.
It was further found that but using this type of Titanium cantilever, its greater rigidity made the use of a longer cantilever possible. This greatly reduces cantilever excursions on heavily modulated records, which offers three advantages:
It is easier for the stylus to track complex, highly modulated grooves.
The resultant smaller coil movement reduces the unlinearities in the magnet field, where the field will "bend" less.
Damping can be reduced, as it becomes easier to control stylus movement.
All the above points help reduce distortions and unlinearities introduced by the cartridge during playback.
As mentioned above, damping of the cantilever is extremely critical. Too much and the cartridge will sound dull, because a lot of the critical energy from the record will be absorbed in the damper instead of reaching the coils, and thereby reducing the efficiency of the vibrational energy transfer from the record as electrical energy in the cartridge. Conversely, too little damping will make the cantilever prone to uncontrolled excursions, resulting in unwanted distortions and poor tracking.
Much experimentation led to a precision Butyl rubber damper, offering a wide operating temperature range and minimal hysteresis effects. The tension on the damper is furthermore adjustable, allowing very accurate set-up of each cartridge's individual suspension.
Finally the assembly is completed with the use of a solid diamond stylus, type van den Hul 1. the main advantages this design offers are described in a separate paragraph, but can briefly be described thus: better tracking of high frequency, lower surface noise, lower record wear, longer stylus life, smaller tip mass and lower tracking force.
The stylus is first "pinched" into place by the cantilever and then glued. using a single component epoxy resin, which needs "baking" for about three hours to harden.
After assembly, each cartridge is subjected to a series of tests, one of which involves a fast dynamic frequency sweep, at high amplitude, this method shows up any undesirable problems in the cartridge. Special test equipment and test. records had to be developed for this process, which is exclusive to Audio Note.
IoLtd requires tonearm with extra 2 wires (6 wires in total) for DC power for energized field. It may require re-earthing of tonearm to avoid hum.
Due to the extremely low output, we do not recommend the use of active moving coil stages for any of the Audio Note cartridges, as they do not offer the linearity and general noise level necessary to get the best yield from the Io cartridges, this requires a transformer.
Audio Note offer two silver wired transformers, the AN-CD and AN-7D, whose quality is consummate with the cartridges, more economic solutions are offered by Audio Note in the form of the ANS~1, ANS~2 & ANS~3 moving coil matching transformers.
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