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CA-70 Modular Mic/Line Amplifier

The CA-70 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.

Each amplifier uses our own custom interchangeable transformers and NOS capacitors, resistors, and octal tubes. With the addition of a flexible pad network, our Negative Feedback tone shaping, and inter-stage volume control, it's like Mid Century with a Modern twist.

CA-70 Amplifier FEATURES:

  • Two-stage 6J7/6C5 vacuum tube circuit
  • 42db-54db of available gain
  • Flexible input pad section for mic or line level operation
  • Transformer balanced. 150 Ohm or 10k input, 600 Ohm output
  • Interchangeable/Optional input and output transformers
  • NOS tubes, signal caps & resistors, PEC 2W carbon pots
  • Up to Six CA Series Amplifiers mount into our PS6 Rack
  • Up to Two Amplifiers in our PS2 Rack
  • Hand Built and Tested in the USA

Two Different Chassis Versions are Available

The PS-6 version is a fully removable module for use with our six channel PS-6 Rack Tray. Each amplifier is easily removable via two thumb screws for flexibility, expandability, and transformer substitution.

The PS-2 version comes factory installed in our PS-2 Rack and PSU. This combines the power supply and modules into a single 3U case creating a compact two channel modular solution. The amplifier and power supply are otherwise identical to our larger PS-6 versions. 

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THE CONTROLS

The (INPUT) Pad section contains a phase reverse switch, and a 5 position attenuation network of Balanced H-pads.

The first four positions are various 150/250 ohm mic pads; -6db, -12db, and -19db. The final (LN) position allows line level signals to run through the amplifier providing tone-shaping capabilities while mixing. It works as both a second-stage booster for other preamps and a summing/buss amp for program and mix material. Two amplifiers can also be chained together to create the multi-stage, high gain recording path of a vintage tube console.

The NF, High, and LOW controls all 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 HIGH switch transitions from the natural openness of the tubes to a gentle filtering of upper frequencies. 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.

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.