The Coil Audio CA-70S tube mic/line amplifier is a 2U mic preamp standalone version of the CA-70 PS6 tube mic/line amplifier and is inspired by vintage two-stage circuit designed by Western Electric in.

The Coil Audio CA-70 uses the exact same American style circuit as the CA-70 PS6 provides a thick tone associated with vintage tube preamps. It also includes Coil Audio’s own CT110HN input and CT-10 output transformers as well as NOS Octal tubes, resistors and high-quality capacitors. 

Controls include Input and Output gain, phase reversal and Negative Feedback to brighten or darken the tone of the preamp by modifying the amount of negative feedback present in the circuit. The Low switch works in combination with the Negative Feedback to boost or cut low-frequency energy. The Hi switch offers gentle filtering of the upper frequencies. The two-stage output features a 6J7 and 6C5 valves with the output control placed between each stage.

The input section has a four-position switch which provides various 150/250Ohms mic pads from 0, -6dB, 12dB, 19dB which also affect the line-level amplification when engaged. Negative Feedback is used to modify the frequency response by increasing its amount into the circuit. A Low switch works in conjunction with the NF switch to boost or reduce the amount of low-frequency energy. Finally, the output control knob is placed between the 1st stage 6J7 and second stage 6C5 tubes and is used to set the final output.