Weight Tank VT-72 Vacuum Tube Microphone Preamp

Inspired by the V72 modules originally built for the German Radio Network, the WT-72 offers 56 dB of gain, which can be driven by a microphone or line level source. The vintage modules only offered 34 dB of gain, so an additional 22 dB of gain is made in the WT-72 with small adjustments to the circuit while maintaining the most sought after tone and character we have all come to love.

Custom input and output transformers, as well as output plate choke help provide the performance and character of its vintage inspiration!

TRUE TO THE ORIGINAL ALL TUBE DESIGN

Just as the vintage design required, the WT-72 employs both AC & DC voltage feedback, providing the proper gain and necessary stability.

QUIET GAIN SWITCHING

The all new WT-72 sets gain with attenuation and altering AC & DC voltage feedback. DC feedback switching would normally introduce large pops, causing harm to your monitors, or even worse, your hearing. The user would need to manually lower monitor volume before switching gain, making for a frustrating experience. A special muting system in the WT-72 performs a brief mute of the output between each step of gain. This mute eliminates the loud transient and allows the tubes to stabilise before the output becomes unmuted.

HYBRID SWITCHING SYSTEM

An 11-position rotary switch utilises both mechanical and photo relays to change the amount of gain,
offering great flexibility.

How It's Done

Gain knob settings Off - 36 dB are switched by attenuating signal to the first EF86, while the remaining 20 dB of gain (36 - 56 dB) are switched by changing AC & DC feedback.

WHY IS ANY OF THIS IMPORTANT?

By changing gain with voltage feedback (gain knob at 36-56 dB), there is less noise at less gain!

For example, at 36 dB of gain, you will have 20 dB less noise than at 56 dB of gain. We are limited with the amount of voltage feedback to change gain because there is a "sweet spot" for stability and frequency response. Therefore, using attenuation before the tube gain stages (gain knob at Off - 36 dB), allows the WT-72 to have the most gain flexibility and best noise performance possible.

TRANSFORMERS
Transformer balanced input and output give the WT-72 the character of the original

TUBE CIRCUITRY
Audio passes through two EF86 tubes giving 56 dB of gain. The signal path contains no solid-state components.

OUTPUT HEADROOM
A plate choke feeding the output EF86 provides large output swings at low distortion.

LINE INPUT
When "Line" is selected from the XLR IN switch, a 36 dB pad is placed before the input TX.

Features

• Mic / Line (XLR) and High Impedance DI Input
  
• DI defeats XLR input when plugged in
  
• Two EF86 equivalent tubes
  
• 56 dB of gain
  
• 11 Position Gain Rotary Switch
  
• Polarity reverse switch
  
• 36 dB pad switch (Line Select)
  
• 48 volt phantom power switch
  
• XLR input and output connections
  
• American input and output transformers and plate choke
  
• White LED indicators for phantom, power on, and output signal present (-12 dBu minimum for illumination)
  
• Hand-built in USA
  
• 115v/230v AC mains option on rear
  
• Internal power supply
  
• 2-year warranty parts and labour
  
  

Specs

• Microphone Mode input load impedance: Approx. 4k Ω
  
• Line Mode input load impedance: 9550 Ω
  
• Output impedance: < 100Ω
  
• 1/4" DI impedance: 500kΩ
  
• 56 dB of gain
  
• Frequency response: 20Hz-20kHz
  
• Maximum output level: +24dBu 
  
• THD+N: <1% S/N ratio: >70dB
  
• Dimensions: 19"w x 3.5"h x 10"d (2u rackspace)
  
• Shipping Weight: 15 lbs.
  
• Power Consumption (120/240VAC): 25 watts