DB - Vacuum Tube Microphone Preamplifier

Download Pro Tools 12 session file: Drivin' Nails in My Coffin. 

QUALITY COMPONENTS

The preamp’s key components are not easily found in modern production models. I tested numerous combinations of transformers, tubes, and coupling capacitors before deciding on the final tonal characteristics that sounded best to me. 

Matched pairs of 1960s new-old-stock General Electric tubes meet or exceed published specifications of transconductance. The GE 5-Star 6072a is legendary for its larger-than-life 3D quality, while the 12BH7 contributes its hi-fi soundstage, tight bass, and neutral highs. 

Jensen has led in transformer research for decades. Their JT115k input transformer is designed for the highest practical 1:10 step-up ratio within their company’s design tolerances. Paired with Jensen's JT-10K61-1M output, these are perfect transformers for a tube preamp. 

Glass-sealed Russian paper-in-oil and Teflon bypass capacitors are used for coupling following tube gain stages. Polypropylene film and electrolytic caps are used elsewhere in the audio and PSU circuits.  

High quality stepped-gain rotary switches are used instead of potentiometers for repeatable gain selection and to help maintain signal integrity. 

Features 

  • 63 dB Gain
  • XLR Inputs/Outputs
  • 1/4" Instrument Input
  • -20 dB PAD 
  • +48V Phantom Power 
  • Ø Polarity Switch 
  • Low Shelving Filters
  • Rear Panel Grounding Lug
  • 120 VAC IEC Fused Power

 
Carefully-Selected Components  

  • Jensen Transformers
  • NOS General Electric 6072a
  • NOS General Electric 12BH7
  • Paper-in-Oil Coupling Capacitors  
  • Teflon Bypass Capacitors  
  • Stepped Attenuators
  • DC Heater Supply
  • Toroidal Power Transformer
  • Turret Board Construction

  
Specifications  

  • 20Hz-20kHz (+/- 0.2 dB)
  • Noise EIN: -125dB (max)
  • Input Impedance 2.4k ohms
  • Output Balanced 600 ohms
  • Low Shelf POS 1: Flat
  • Low Shelf POS 2: -3dB at 75Hz
  • Low Shelf POS 3: -3dB at 275Hz
  • Dim (3U): 19" W x 5.25" H x 11" D
  • Weight: 19.0 lb

 

    TWO CHANNELS OF TUBE PREAMP FOR JUST 1,999.99