Feron – Grain-Oriented Silicon Iron

Feron is not a “normal transformer core” but a rigorous material and process decision: it is based on grain-oriented silicon iron, a high-performance electrical steel whose properties are determined not only by the material itself but above all by its crystallographic orientation. During manufacture, the sheet is rolled in several stages and subsequently annealed; this deliberately orders the microstructure so that, along the desired direction, the metal lattices develop particularly favorable magnetic permeability and controlled magnetization-reversal behavior. This class of material is used not only in high-quality transformers but also in the output transformers of tube amplifiers – precisely where lowest losses, minimal distortion and a wide usable frequency range are decisive.

The difference from ordinary transformer laminations is fundamental: standard laminations are usually coarser, thicker and not consistently grain-oriented. They exhibit higher eddy-current and magnetization-reversal losses and tend toward audible nonlinearity under load. Feron, by contrast, operates with very low hysteresis, high saturation flux density and controlled loss behavior. The lamination thickness of 0.35 mm – combined with high-quality insulation between the laminations – reduces the unavoidable eddy-current losses compared with standard laminations and keeps them low even in the audio range.

A further practical advantage is the magnetic efficiency: thanks to the strong magnetic effectiveness of the core, Feron inductors can be designed to achieve an exceptionally low DC resistance (RDC) for a given inductance – frequently combined with a compact size. This is particularly valuable in the bass and lower midrange, because RDC directly determines level, damping and control. In combination with suitable core designs (I-core, transformer core/E-core, zero-ohm core with a defined air gap), this potential can be exploited deliberately without “buying into” the typical core-related side effects. The result is an inductor that works cleanly both at high currents and at low levels.

Sonically, Feron is the first choice among core materials. It combines maximum dynamic reserve with exceptional composure under load: bass impulses are not compressed, and the sound picture remains stable, controlled and free of harshness even at high levels. At the same time, the basic distortion is so low that Feron – used correctly – can also be employed in more sensitive areas where air-core coils would otherwise be preferred. Feron core inductors are thus the answer to the classic trade-off question of crossover practice: compact design, low resistance and high power handling – with maximum sonic composure.

Feron Core Designs

I-Core Inductor (bar core made of Feron sheet)

The I-core inductor is the simplest Feron design: a bar core (I-core) made of grain-oriented Feron sheet passes through the winding. Comparatively little Feron is thus available in the magnetic circuit – the field-strengthening effect is lower than with E-core or E+I constructions. It is an affordable, very compact Feron inductor that is easy to integrate without having to forgo the special material advantages of the Feron sheet.

Electrically, the lower core effect means: for a desired inductance, the I-core inductor needs more copper than a larger, closed core circuit. The achievable DC resistance (RDC) at the same inductance is therefore higher than with an E-core or zero-ohm design – in return, the design remains small and economical. In practice, within the compact core-inductor class it is considerably more robust under load, and lower RDC values can be realized than with geometrically comparable Aronit or ferrite core inductors. At the same time – thanks to Feron – the signal remains very clean even under load, because basic distortion from magnetization reversal is kept extremely low and saturation distortion does not come into play even at party levels or in PA applications. In short: compact, PCB-mountable – and still robust.

It is frequently mounted on the PCB. That makes it very attractive from a system perspective, but it demands discipline in the layout. For PCB-mounted inductors, the stray field must be factored into the design: distance from sensitive signal paths, from other inductors and from magnetically susceptible components, sensible orientation of the axes, and altogether clean field management through placement.

Field of application

I-core inductors are ideal when a Feron core inductor is to be compact, PCB-mountable and attractively priced, yet more robust under load than the usual small core-inductor families.

Acoustic properties

• Very good control and dynamics in a compact design
• Very robust operation

E-Core Inductor (transformer core inductor)

The transformer core inductor works with an E-shaped core made of Feron sheet. Compared with the I-core, considerably more Feron is available in the magnetic circuit. The field-strengthening effect is substantially higher: less winding effort is required for a given inductance, and precisely this is the source of the central advantage of this design.

In practice this means: at high inductance, E-core inductors achieve a comparatively much lower RDC than I-core inductors. This is especially valuable when an inductor is used in the bass or lower midrange and the series resistance directly determines efficiency, damping and control. At the same time – thanks to Feron – the signal remains very clean even under load, because basic distortion from magnetization reversal is kept extremely low and saturation distortion does not come into play even at party levels or in PA applications.

The E-core shape also has structural consequences: these inductors are typically fastened not on the PCB but directly in the cabinet. There are two reasons for this: first, E-core inductors for high inductances and low resistance are often larger and heavier; second, mechanical fastening in the cabinet (rigid, decoupled, defined) is frequently the better way to keep the entire crossover permanently stable and magnetically clean.

Field of application

E-core inductors are the right choice when low RDC is to be combined with high inductance and the inductor does not necessarily have to be PCB-mounted. They are the “classic powerhouse solution” within the Feron family: very efficient in the magnetic circuit, very strong in the ratio of inductance to resistance.

Acoustic properties

• Extreme control and level stability thanks to a very low series resistance
• Very calm, clean reproduction even under dynamics and load
• Particularly strong in the bass/lower midrange, where RDC is directly audible
• Maximum composure at high currents

Zero-Ohm Inductor

The zero-ohm inductor is the most rigorous Feron core design. It uses the E-core and I-core together – so this design places the most Feron in the magnetic circuit. It additionally has a defined air gap, which guarantees high power handling even in small designs. This combination is the key: maximum core effect with sufficient level reserves. The larger sizes are suitable not only for party use but also for PA applications.

Thanks to the maximum amount of Feron in the magnetic circuit, the zero-ohm inductor achieves extremely low ohmic resistances (RDC) at comparable inductance that are otherwise scarcely realizable. That is precisely its purpose: where the series resistance of the inductor would be the dominant limiting factor, the zero-ohm design reduces the resistance to a minimum. In applications with high currents this is a massive gain in efficiency and control – and it changes the behavior of the loudspeaker system directly, because the electrical damping of the amplifier takes maximum effect.

Like the E-core inductor, the zero-ohm inductor is typically fastened in the cabinet rather than mounted on the PCB. Size, weight and the importance of mechanical fixing clearly favor this. Moreover, this allows the field management and the arrangement relative to other components in the crossover to be designed rigorously.

Field of application

Zero-ohm is the design for uncompromising applications in which the RDC must be as low as possible – combined with high inductance. Maximum magnetic circuit, minimum resistance.

Acoustic properties

• Maximum bass control and dynamics thanks to extremely low series resistance
• Great composure at high currents
• Convincing in demanding low-frequency branches