Thrax Audio strikes again! Meet the all new Thrax Libra differential balanced 300b tube preamplifier; 300B at point-blank... "Experience a full 300B signal path! Libra is the latest masterpiece by Thrax - a follow-up on the concept of Spartacus 300 reimagining Directly Heated Triodes in application with advanced magnetic materials. A take-no-prisoners approach to line-level preamplifiers, based on the legendary Western Electric 300B tube."

It uses two 300B tubes per channel in true dual mono differential pure class-A triode operation to form a gain stage so unique it pushes the tonal spectrum of the Spartacus 300 power amplifiers to reveal deeper layers of unexpected information in the recordings. Libra paired with Spartacus 300 allows users to experience - and be awed by - a full 300B signal amplification path for the first time.

But we didn’t stop there. Libra features two independent outputs that can be gain- offset from each other to allow for bi-amplification with different amplifiers for mid/hi and bass. For example a single-ended triode amplifier for mids/highs and a powerful push-pull amplifier for low frequencies. The offset feature lets you adjust the preamp for amplifiers with different gain and keeps their volume level in sync.


Libra overcomes another limit with the Tape Loop feature

Another unique feature of Libra is the fully balanced Tape Loop allowing the use of professional tape recorders like Studer, Ampex, and many others so you can take full advantage of the quality of your master tapes. A home cinema bypass is also available for those wishing to integrate the stereo system in their media room. And the amplifiers can be powered on and off remotely for installations where they’re not easily accessible.

For us the ultimate task was to create a pre-amplifier worthy of driving the Spartacus 300 power amplifiers - well-known for their ability to preserve the tone and texture in the signal at all levels, while not constraining the dynamic expression or imposing any coloration upon it.

As explained on our other amplifier product pages on our website, each stage has to have much lower distortion and noise than the following in order not to influence the resulting harmonic spectrum. So Libra had to be as good or better than the 300b input stage of the Spartacus 300 in order not to affect its sound. But we are already using one of the most linear tubes there, so the choice was an inductively loaded heavy class A differential stage cancelling the Libra 300b’s negligible 2nd harmonic leaving the spectrum absolutely clean.

DHT tubes require a lot of auxiliary electronics for optimal operation, so in this case we have split the unit in two parts - a power supply module and the active unit. This keeps all mains AC and rectifier noise in a separate box while final regulation and filtering is still kept adjacent to each element in the amplification circuit. Everything is microprocessor-controlled with a large color LCD showing the unit’s status clearly visible from wherever you are seated.

  • Custom current production tubes for long life
  • Balanced differential topology for noise immunitysubtle dynamics
  • Auto bias for compensation of tube ageing and correct operation of any 300B
  • Current sourced regulator for stable power allowing explosive dynamics and tonal purity
  • DC coupled input and output for ultimate transparency
  • Microprocessor controlled operation for safety
  • Special filament heating circuit for harmonic richness and tube protection
  • Separate dual mono power supply

Libra should not be merely talked about - it must be listened to! So please feel invited to the first public performance to be held during the Paris audio show 7-8th December at: Paris Marriott Rive Gauche Hotel & Conference Center