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Coil Audio CA-70S Single Channel Mic/Line Amplifier

Single channel mic/line amp based on the elegant and simple single-ended two-stage circuit design invented by Western Electric in 1913


Product Description

The Coil Audio CA-70S Single Channel Mic/Line Amplifier is based on a two-stage circuit invented by Western Electric in 1913. It was licensed and built by various audio manufacturers from the 1930s through the 1950s. RCA, Gates, Western Electric, and Langevin were just a few that utilized this elegant and simple single-ended design. With the addition of a flexible input pad network, Coil's Negative Feedback tone shaping, and inter-stage volume control, it's like Mid Century with a Modern twist.

Each amplifier utilizes CT110HN and CT41 custom transformers, as well as the same high end and vintage components as our larger PS6 modules.


The (INPUT) Pad section contains a Mic/Line selector, phase reverse switch, and a 4 position attenuation network of Balanced H-pads.

The LINE/MIC switch toggles between LINE or MICROPHONE level inputs. Select “MIC” for standard low level microphone signals. Select “LINE” for any balanced line level signal such as the output from a tape machine, DAW, mixer, keyboard, drum machine, or other pre amps. “LINE” mode allows it to work as a tone shaper/booster for other outboard gear, a second-stage booster for other preamps, or a summing/buss amp for program or mix material. It also enables easy chaining of multiple amplifiers to create the multi-stage, high gain signal path of a vintage tube console.

The Rotary Selector switches between 0, -6, -12, and -19 dB input pads. This allows the input to handle high output microphones or loud signal sources. These pads are in the path whether you are in “LINE “ or “MIC” mode.

The NF and LOW controls interact to create a unique tone-shaping circuit. The NF control varies the amount of Negative Feedback present in the circuit. Counter-clockwise brightens and moves the sound forward while raising harmonics and sensitivity. Turning it clockwise increases negative feedback, producing a darker tone with a smooth, dampened harmonic structure. The LOW switch reacts with the NF, boosting or cutting low frequency while moving the low end from front to back in the sound stage. Most effective when the NF knob is between 11:00 and 5:00, The more Negative Feedback, the more reactive.

The OUTPUT control knob is placed between the 1st stage 6J7 and 2nd stage 6C5 tubes. It sets the final level and offers further control of the two-stage gain structure.


  • 2U steel enclosure with integrated power supply
  • CT-110HN high Nickel input, and CT-41 output transformers installed
  • Two-stage 6J7/6C5 vacuum tube singe ended circuit
  • 42db-54db of available gain
  • Flexible input pad section for mic or line level operation
  • Transformer balanced. 150 Ohm mic input, 20k Bridging line input, 600 Ohm output
  • NOS tubes, signal caps & resistors, PEC 2W carbon pots
  • Linear regulated Power Supply with slow B+ ramping to prolong tube life
  • Hand Built and Tested in the USA

Product Specifications

Condition New
Tube or Solid State Tube
Channels Single-Channel
Chassis 19-inch Rack-mount
Rack Spaces 2U
Input Connectors Analog XLR
Output Connectors Analog XLR
Tube Complement 6C5, 6J7

Product Reviews

5 out of 5 stars.
Review Count (3)

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Beautiful vintage sound, this one will never leave my rack.

By Chuck S on January 15, 2023

Thick and super versatile.

By Thomas L on December 27, 2021

An incredible pre-amp. New classic.

By Richard on October 18, 2019

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In almost 20 years in Pro audio buying, never did I receive a unit so well packed and exactly as described. Works flawlessly. The whole process has been so smooth. I will never hesitate to do business with you guys in the future and will recommend you to everyone I know.
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This was my first experience buying something from Vintage King (although I surf the "used" categories on the website frequently!), and, despite being on the other side of the world, I had absolutely no trouble and everything went very smoothly.
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