The Accuphase C-3900 features a specific connection designed to bypass its internal preamplification stage. This input allows users to integrate an external signal processing unit, such as a dedicated phono stage or another preamplifier, directly into the signal path. Essentially, it provides a direct conduit to the C-3900’s volume control and subsequent amplification stages, effectively utilizing the C-3900 as a high-quality control amplifier.
This feature enhances system flexibility and allows for sonic tailoring based on user preference or the specific characteristics of the source material. For instance, audiophiles might employ a specialized phono preamplifier known for its exceptional performance with vinyl records and then route that signal through the designated input. The benefit lies in bypassing the built-in preamplifier circuitry of the C-3900, potentially minimizing coloration and maximizing the sonic fidelity of the external unit. Historically, such features have catered to enthusiasts who appreciate modular audio systems and the ability to optimize each component for a specific task.