The Audes ST-900 power conditioner is designed to supply electrical power to high-end AV and hi-fi equipment. It features five sockets with a total handled power of 900 W. The main element of the device is a 230 VAC/115 + 115 VAC toroidal balancing transformer designed and developed by Audes, which isolates the equipment from the mains supply. Despite the significant power rating of such transformers, the construction of the power conditioner completely excludes harmful electromagnetic radiation.

A special transformer winding technique and a high-quality transformer core are used. Firstly, they provide a filtering effect. The ST-900 transformer was designed to function as a low-pass filter with a cut-off at 800 Hz, since all mains interference occurs at much higher frequencies. Secondly, the filtering effect is caused by the self-induction of a very large core, meaning the magnetic flux cannot change instantaneously under a transient disturbance. Finally, if there is a DC offset in the mains supply, the transformer prevents it from reaching the equipment connected to the power conditioner. The high-quality CEE 7/3 sockets are galvanically isolated from the external mains network. The transformer is equipped with a reliable electrostatic shield. Incoming electrical interference is counteracted using a mutual cancellation principle. The secondary winding of the transformer is split into two halves and has an artificial centre tap, which is connected to the earth terminals of each power socket. All of the above technical features make it possible to almost completely eliminate mains noise, providing a reliable, high-quality power supply to audio equipment.

The use of the ST-900 with any AV equipment, including valve and solid-state devices, improves sound reproduction quality. The most significant results are achieved when the power conditioner is used with power amplifiers. During highly dynamic parts of an audio track, a powerful amplifier must draw substantial current peaks from a power supply, which can reach magnitudes of 50 to 100 A, whilst maintaining voltage levels without sags. An ordinary domestic socket, which is connected to a distribution board via long electrical cables, is not capable of providing such current levels due to the relatively high output impedance. The ST-900 has a very small output DC resistance, so it can easily supply high current peaks without encountering voltage drops. This is achieved through the use of a transformer with a very large core and a large number of turns on the primary winding. As a result, inductance is minimised. In turn, the response time of a power amplifier to a changing audio signal is reduced, which benefits transient reproduction, especially in lower frequency bands. An audio reproduction system exhibits a wider dynamic range.

Audes power conditioners have overload protection and thermal protection, which switches off the transformer if the transformer temperature reaches 90 °C. Once the temperature drops to 75 °C, the device will reconnect to the mains supply automatically.

The ST-900 comes without an integrated DC blocker. An ST-900DC version is available, which has a built-in DC blocker.