The Locomotive Audio Copperline is a utility unit designed to be placed between a microphone and a microphone preamp or between two line-level devices to alter the signal and shape the sound creatively or assist vintage mic preamps.. 

The Locomotive Audio Copperline has a 5-position attenuator, a 5-position high pass filter, mute, vintage load, polarity, and never-before-seen variable voltage phantom power.

The Locomotive Copperline uses a unique slow-start phantom power, gradually raising the phantom voltage over 5 seconds, preventing voltage transients resulting in turn-on pops and protecting vintage input transformers. 

It also features a variable voltage phantom power, providing up to 52 volts of phantom power from a high-current, low-noise supply. It will make your microphones sound more detailed and transient-rich than low-cost supplies or outboard preamps that treat phantom power as an afterthought.

Furthermore, a Vintage "Ohm" load adds an 825 Ohms resistor between pin two and pin 3 of the microphone input. Some vintage units, however, require 600 Ohm to behave correctly, so the Copperline makes it possible to switch between the two.