BC109 AL28

About the BC109 AL28

The Blue Circle BC109 AL28 is a custom, special-order version of Blue Circle Audio's BC109 solid-state line-stage preamplifier, built to customer specifications with greatly increased power-supply capacitance and an upgraded Shallco stepped attenuator for volume control. It is based on the standard BC109 platform, which uses a very large capacitor bank capable of powering the preamp for hours without AC, and can be further expanded via Blue Circle's custom CP-series supercapacitor supplies. The AL28 configuration denotes a custom build rather than a fixed catalog model, so details like total capacitance and the exact implementation of the Shallco attenuator are determined case-by-case by Blue Circle, focusing on very low noise, high dynamic headroom, and refined sonic performance. While the BC109 name originates from a classic low-noise NPN transistor designation, Blue Circle's BC109 preamplifier is a complete audio component and should not be described in terms of discrete transistor datasheet specifications (package type, switching use, dB noise figure), which belong to the historical BC109 transistor and not to this preamp. Subjective traits commonly associated with the BC109 platform in reviews and owner reports include an open, airy treble, natural midrange, and powerful, articulate bass, but these characteristics are implementation- and system-dependent rather than formally specified by the manufacturer.