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Yamaha AST-A90M

Active Servo Processing Amplifier

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Yamaha AST-A90M


The Yamaha AST-A9OM, unlike any existing amplifier, is an amplifier that can have a negative resistance figure in its output impedance.

The voice coil impedance of a conventional speaker is approximately 6 ohms, and the AST-A9OM can apply a negative resistance to eliminate this voice coil resistance portion.

As a result, with the combination of the AST-A901M and the AST System exclusive speakers (AST-SV90 etc), the resistance between the amplifier and speakers will become approximately 0 ohms and the electrical current will be able to run infinitely (condition close to superconductivity).

In other words, the amplifier output voltage will directly drive the speakers, hence making it possible to provide a powerful driving force and damping power of steady speed operation.

Because an element possessing a negative resistance figure does not exist in nature, we have developed this by way of electrical circuits in the AST-A90M.

If the type of speakers varies, the negative resistance figure will be different. Accordingly, we have developed the negative resistance producing circuit into a cartridge form to apply to various AST speakers.

In addition, with the utilization of the Air Woofer system in which the air in the port functions as a diaphragm, the distortion is considerably retained in the low range to enable high-quality enjoyment of bass.


Power output: 45 watts per channel into 6Ω (stereo)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 0.09%

Input sensitivity: 2.5mV (MM), 150mV (line)

Signal to noise ratio: 80dB (MM), 92dB (line)

Channel separation: 50dB (MM), 50dB (line)

Output: 150mV (line)

Dimensions: 366 x 124 x 328mm

Weight: 6.7kg

Accessories: learning remote control



This website is not affiliated with or sponsored by Yamaha. To purchase AST-A90M spares or accessories, please contact the company via their website or visit an authorised retailer.