Fidelix STACCATO Electrostatic Headphone Amplifier

STACCATO is characterized by the extremely pure bias voltage obtained by the Clean Bias Technology (CBT) technique. Of course, it is an all-FET complete DC amplifier, which is a fidelix commitment, and it is also a Class A real-time BTL.

With CBT, almost no ripple voltage is produced because almost no bias current flows. The basic principle is that if ripple exists on the amplifier side, the same amount of ripple is added to the bias side, resulting in a clean true bias voltage after subtraction. This results in an overwhelmingly clear, delicate, yet vivid sound.

Condenser-type headphones are not good at excessive loudness. A powerful amplifier might help, but it could damage the headphones. Therefore, we introduced the soft clip technique, which makes the clips inconspicuous, as shown in the photo. Since the clip is not noticeable, the maximum volume can be empirically increased by about 2 dB. The MOS-FET, which does not cause carrier accumulation effect (left side of the picture below), has successfully achieved this. 400Vrms was measured with a 100:1 probe, but almost 400Vrms was obtained.

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

Even the power transformers are independent left and right, connected in opposite directions to cancel leakage flux, and diode-isolator type, so that even the left and right grounds are completely separated in effect.

The XLR input requires a quadruple volume in a normal design, but the circuit can be used with a double volume, thus halving the effect of the volume on sound quality. The main resistors are non-magnetic resistors manufactured by PRP in the U.S., the load resistors are metal oxide film resistors manufactured by VISHAY in parallel, and PPS capacitors are used. The power supply consists of a simple ± 300 V power supply only, and uses SiC rectifier diodes that do not generate recovery noise. By eliminating the contact points of connectors and relays, contact failure and deterioration of sound quality after long-term use are eliminated. The top panel is used as a heat sink to achieve the ultimate performance in a compact, lightweight, and inexpensive package.

The designer, who was also involved in the design and development of STACCATO, planned this amplifier as a product that he wanted to continue using. The designer himself is confident and convinced that this amplifier can be used as a reference product. It is a headphone amp that demonstrates the true value of condenser headphones, worthy of the name "STACCATO".