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  System Design

Bandwidth Specialization of Amplifier

Typical amplifiers must operate over the full frequency bandwidth - it is very difficult to design an amplifier to perform well at all frequencies at wide-ranging power levels. In addition to this challenge, performance expectations can be further reduced because few, if any, amplifiers are ever optimized to work with one specific loudspeaker. The Integris Active 300B uses three amplifiers per channel, each set up and fine-tuned to operate within different parts of the audible frequency spectrum. Furthermore, each will operate with only one known loudspeaker drive-unit and is optimized to enhance overall performance with that drive unit.

High power amplifiers and low power amplifiers typically have their individual strengths and weaknesses, as do different solid-state and vacuum tube amplifier topologies. Also it is a difficult balancing act to have a full-range amplifier perform reasonably well across a broad range of frequencies. The Integris Active 300B uses different types of amplifiers where they work best in different frequency ranges. A high power solid-state output stage delivers low frequency dynamics and authority. Low power vacuum tube amplifiers deliver clear, lively, and delicate performance in the midrange and treble.

The Active 300B high and mid frequency amplifier sections are based on the very highly regarded 300B single-ended triode circuit. The low-level vacuum tubes are the equally renowned 6SN7 type. All circuits are run at fairly conservative operating points where they sound their best and will allow the tubes to have a long life. Crossover filters are designed within the coupling circuits of each amplifier stage - there are very few extra components compared to most similar SET amplifier designs. Toroidal output transformers designed by renowned transformer designer Menno Vanderveen and built by Plitron are customized for superior performance into the mid and high frequency ranges - a significant advantage over normal full-range transformers. The critically important bypass capacitors are small value polypropylene-film Auricaps rather than large value electrolytics.

The low frequency power amplifier delivers high power capability and control in an implementation designed for excellent low frequency performance and sonic integration with the higher range amplifier systems. The power amplifier module is designed and built by renowned amplifier manufacturer Bryston. Super-low output impedance and a dedicated power supply using a massive Plitron toroidal power transformer, large DC filter capacitors and superfast rectifiers ensure tremendous control of the woofer. Crossover filtering is initiated using the same 6SN7 and gain circuit as the mid and high sections and solid-state based active filters follow it. The filters also shape the low frequency response to extend in-room bass performance smoothly down to the infrasonic range, rivaling that of the best active subwoofers.

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