The Locomotive Audio Copperline is a dual-channel utility tool designed for placement between microphones and preamps or between two line-level devices, offering engineers an adaptable and sonically transparent signal-shaping unit. Its robust feature set includes variable voltage phantom power, slow-start phantom supply, high-pass filtering, attenuation, polarity switching, a mute circuit, and a unique Vintage Ω load option. This combination of features enables refined control over gain staging, tonal shaping, and signal compatibility across a wide variety of recording configurations.
At the core of the Locomotive Audio Copperline is its patent-pending Variable Voltage Phantom Power, which allows engineers to manipulate the voltage fed to condenser microphones, from the full 52V down to much lower levels, revealing new sonic textures and creative possibilities. This feature empowers users to alter microphone behaviour deliberately, potentially lowering headroom, shifting tonal balance, or introducing mild saturation depending on the mic’s design. Despite the experimental nature of this feature, it is completely safe for all phantom-powered microphones.
Complementing this is the The Locomotive Audio Copperline is a two-channel utility unit designed to sit between microphones and preamps or line-level devices, offering precision control over signal flow. It features a 5-position attenuator, high-pass filter, mute, polarity switch, Vintage Ω load, and patent-pending Variable Voltage Phantom Power. With slow-start phantom protection and creative signal-shaping options, it allows engineers to explore new tonal possibilities while protecting vintage gear and maintaining sonic integrity.
Locomotive Audio Copperline’s Slow-Start Phantom Power, which ramps voltage over five seconds to protect sensitive vintage transformers from voltage spikes, especially when connected to preamps not designed to handle abrupt phantom voltage delivery. This makes the unit ideal for integrating classic gear into modern workflows without compromising longevity or performance.
Each of the two channels includes a 5-position high-pass filter (off, 45 Hz, 75 Hz, 150 Hz, 300 Hz), using a custom-wound, mu-metal shielded inductor. The filter’s cutoff frequencies are dependent on the source impedance of the connected mic, typically calculated for microphones with around 150Ω impedance. This design delivers clean and musically responsive low-end control, suitable for anything from vocal tightening to rumble removal in instrument recordings.
The Locomotive Audio Copperline also features a 5-position rotary pad attenuator offering attenuation at unity, -15 dB, -20 dB, -30 dB, and -40 dB. When set to attenuation, the input impedance is approximately 1200–1500Ω, optimised for level management without sonic degradation. In unity mode, the Locomotive Audio Copperline’s impedance is defined by the downstream connected device, maintaining signal integrity in less intrusive scenarios.
Another standout is the Vintage Ω switch, which places an 825Ω resistor across the input to simulate a 600Ω load. This is particularly useful when connecting to high-impedance inputs, restoring the appropriate loading conditions required by some vintage gear to perform optimally. The impedance interaction is thoughtfully calculated, even when attenuation is engaged, ensuring useful results across a range of gear pairings.
Rounding out the feature set is a phase (polarity) reversal switch, a mute switch for silent troubleshooting or live use, and a compact yet rugged design that enables creative signal routing. For even deeper control, engineers can chain both channels in series, either to stack high-pass filters, achieve up to 60 dB of attenuation, or experiment with combined filtering and voltage effects.
Designed by producer and co-inventor Will Edwards, the Locomotive Audio Copperline addresses real-world studio challenges with a feature set aimed at problem-solving, creative exploration, and gear preservation. From handling mismatched signal paths to unlocking new microphone tones, the Locomotive Audio Copperline is a unique and essential signal toolbox for engineers seeking both utility and inspiration.
