The Coil Audio CA-70 Preamp 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 Coil Audio CA-70 Preamp uses their own custom interchangeable transformers and NOS capacitors, resistors, and octal tubes. With the addition of a flexible pad network, the Negative Feedback tone shaping, and inter-stage volume control, it's like Mid Century with a Modern twist. You must have the Coil Audio PS6 Rack to power the Coil Audio CA-70 Preamp.
Coil Audio CA-70 Preamp Contols
- 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; -6 db, -12 db, and -19 db. 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.
Coil Audio CA-286 Preamp Transformer Options
Preamp Input Transformer
- CT-110: A nickel/iron microphone input transformer based on a punchy 1960s small signal coil. It's perfect for all-around use and excels at high transient material. Its design gives it a very forward and rich mid-range, with smooth saturation in the highs and lows.
- CT-110HN: A super-mu microphone input transformer based on a rare 1950s hi-fidelity coil. Detail oriented, it adds an excellent top and bottom extension, and smooth, breathy saturation.
Line Input Transformer
- CT-41: A line output (or input) transformer based on a popular 1960s Peerless design. Frequency response is ruler flat from 20Hz to 30kHz, dipping just below 1db at 60kHz. Its smooth saturation imparts a rich, wooly, and hi-fi sound to anything that runs through it.
- CT-11: A Universal 1:1 line isolation transformer. Based on another 1950s coil design, it imparts a rich, hi-fi sound to any signal. The impressive frequency response of +/- .5db from 20Hz - 60kHz make it an unbeatable performer for isolation or balancing unbalanced signals and devices.
Coil Audio CA-70 Preamp 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
- Hand Built and Tested in the USA
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