Z-Foil resistors for high-end audio applications

Posted By : Nat Bowers
Z-Foil resistors for high-end audio applications

Vishay Precision Group has today released a new series of ultra-high-precision through-hole Z-Foil resistors, the AUR series. Offering low noise and low inductance/capacitance, the new conformally coated and low-profile AUR series resistors are designed for high-end audio applications that require distortion-free properties.

Featuring load-life stability to ±0.01% after 2,000 hours at +70°C, the AUR series devices offer low TCR down to 0.05 ppm/°C nominal from 0°C to +60°C, +25°C ref, and tolerances down to ±0.01%.

Resistors must be carefully selected for high-end audio equipment, this is one of the best ways to minimize noise and distortion in the signal path. A typical audio amplifier consists of a voltage preamplifier, which deals with low-level signals making the intrinsic noise of resistors critical, and a power amplifier, which requires high linearity of amplification and minimal dynamic distortion. With a cold-rolled metal alloy foil, Bulk Metal Foil AUR resistors meet both of these requirements. Their construction eliminates any current noise in the element itself and provides the linearity that preserves signal integrity with no clipping or roll-off at signal.

Yuval Hernik, senior director of application engineering for VFR, comments: "Many users of precision audio equipment... resign themselves to making constant adjustments and troubleshooting, but in fact these can be avoided. Instability is often traceable to a few supposedly fixed resistors that are not really fixed at all. If these resistors would only retain their original values, there would be no need for costly controls and other compensating circuitry."

Further reducing signal distortion whilst increasing clarity in signal processing, the AUR devices also feature a special "noise-free" design, with special in-house stabilization. The current in adjacent current-carrying paths runs in opposing directions while path-to-path capacitances are connected in series, cancelling the paths' parasitic inductance and minimizing the parasitic capacitance of the resistor, respectively.

"Microphonic noise is a parasitic effect mostly associated with surface-mounted resistors. The plane of the mounted resistive element is parallel to the board, by which vibrational movement induces spurious signals much like a diaphragm in a speaker system. The horizontal resistor element produces the same microphonic effect, whether caused by physical vibration of the board or by strong sonic waves impinging on it," adds Hernik.

With a resistance range from 5 Ω to 120 kΩ, users can specify AUR series resistors with any conceivable ohmic value within this range, to six digits, at no additional cost or lead time. The resistors feature rated power to 300 mW at +70°C, thermal stabilization time of <1 s (within 10 ppm of steady state value), and a voltage coefficient of <0.1 ppm/V. Other features include a maximum working voltage of 300 V, a rise time of 1 ns with effectively no ringing, and current noise of <0.010 μVrms/V of applied voltage (<-40 dB).

Hernik concluded: "Through-hole devices achieve better stability because they are not subjected to thermomechanical stresses from the PCB. And unlike other through-hole resistors, the AUR devices require no added height for stress-relieving bends in the leads, as they feature built-in stress relief."

The AUR series resistors are available now for sampling and production quantities. Lead times are two weeks for samples and eight weeks for standard orders.


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