GMX-KIT - Transconductance Multiplier


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The "GmX" effect is the difference of sound between a 50W amp with two power tubes and a 100W amp with four power tubes. The effect is described in the Plexi chapter of our book The Ultimate Tone, Vol. 3 (TUT3) and taken to extremes in our book TUT4. Now any push-pull tube amp can have the feel of a much larger amp with the simple addition of the GMX-KIT. A pot provides continuously variable control over how much of the GmX effect is added.

As a "feel enhancer" the GMX-KIT requires minimal heat-sinking; bolting it to the chassis will suffice. For use as a "power enhancer", more significant cooling is required.

The GMX-KIT can be used in any push-pull amplifier, whether cathode-biased or fixed-biased - up to 400W nominal output and with supply voltages up to 800Vdc. PCB construction shortens assembly time and assures proper voltage spacings.

The GMX-KIT board has provisions for adding meter jacks to monitor the tube currents as part of normal biasing procedures.

Standard wiring uses the plate supply to support GMX-KIT's control circuitry. Provisions on the PCB allow our Opamp Supply Derived from Heater (PSU-OPA) split-rail supply to be used, in turn allowing a chip upgrade for slightly better performance.

Instructions included.

PCB size: 4.55" x 2" (116mm x 51mm)

About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

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