Fidelix STACCATO Electrostatic Headphone Amplifier

The STACCATO is characterized by the fact that it uses a technology called Clean Bias Technology (CBT) to obtain an extremely pure bias voltage. Of course, it is a complete DC amplifier with all FETs, which is fidelix's specialty, and it is also a Class A real-time BTL.

In CBT, almost no bias current flows, so there is almost no ripple voltage. The basic principle is that if ripple is present on the amplifier side, the true bias voltage subtracted by adding the same amount to the bias side will be clean. As a result, we can obtain an overwhelmingly clear, delicate, yet vivid sound.

Condenser headphones are not good at excessively loud volumes. It seems that it would be good if the amplifier was powerful, but there is a risk of breaking the headphones. Therefore, we introduced a soft clip technique that makes the clip less noticeable as shown in the photo. Since the clip is not noticeable, you can increase the maximum volume by about 2 dB in your experience. This was successfully achieved by using a MOS-FET that does not produce a carrier accumulation effect (left side of the photo below). It is a measurement with a 100:1 probe, but almost 400 Vrms is emitted.

The square wave response at 100kHz with a 100pF load is quite beautiful. (Right side of the photo)

Even the power transformer is configured in a left and right independent configuration, and it is connected in the opposite direction to cancel the leakage flux, and the diode isolator system effectively separates the left and right grounds.

The XLR input normally requires a quadruple volume, but by using a circuit that can be used with a double volume, the impact of volume on sound quality has been halved. The main resistor is a non-magnetic resistor from PRP in the United States, a metal oxide film resistor from VISHAY is used in parallel for the load resistor, and PPS is used for the capacitor. The power supply consists only of a simple ± 300V power supply, and uses SiC for the rectifier diode that does not generate recovery noise. By eliminating the contacts between the connector and the relay, poor contact and deterioration of sound quality have been eliminated when used for a long time. With a clever design, such as using the top plate as a heat sink, we have challenged the ultimate performance in a small, lightweight, and inexpensive manner.

The amplifier was planned by a designer who was also involved in the design and development of Stax as a product that he wanted to continue using, but the designer himself was confident that it could be used as a reference, and the transparency as if you could see the distant scenery and the outline of the bass instrument became clear and the sense of rhythm came out vividly. It is a headphone amplifier that demonstrates the true value of condenser headphones that are worthy of the name STACCATO.