LIBRA
DIFFERENTIAL BALANCED 300B TUBE PREAMPLIFIER
Statement differential balanced 300B tube preamplifier of the 21st century.
Features
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Post amplification volume control for lowest noise
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Modular construction
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External dual mono power supp-ly with choke input rectifier for lowest switching noise
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Programmable Balanced Tape loop
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Stepped volume control for perfect repeatability of level settings
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Interlocking solid aluminum chassis
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RCA and XLR inputs with adjustable sensitivity controls
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Highest quality long life 300B tubes
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Single gain stage
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Dual balanced output for bi-amping with offset adjustment
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Home Theatre bypass feature for integration in Home Cinema systems
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Microprocessor-controlled opera-tion for safety
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Special filament heating circuit for harmonic richness and tube protection
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Current sourced regulator for stable power-allowing explosive dynamics and tonal purity
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DC-coupled input and output for ultimate transparency
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Balanced differential topology for noise immunity & subtle dynamics
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Auto-bias for compensation of tube aging and correct operation of any 300B
Libra employs two 300B tubes per channel in true dual mono differential pure class A triode operation to form a gain stage so unique that presents a tonal spectrum that is dense and clear revealing extra layers of unexpected information in the recordings. Libra paired with the Thrax Spartacus 300 allows users to experience a full 300b signal amplification path for the first time and be stunned by it.
Libra features two independent outputs that can be 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 mid/hi and a powerful push-pull amplifier for the Low frequencies. The offset lets you adjust for the different gain of the amplifiers and keeps their volume levels in sync.
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 a media room. A “trigger out” function is provided for turning amplifiers in hard-to-reach places on or off automatically when powering on your preamp.
Our goal was to create a pre-amplifier worthy of driving the Spartacus 300 power amplifiers known for their ability to preserve the signal’s tone and texture at all levels, not constraining the dynamic expression or imposing any coloration to it. Libra had to be at the uncompromising level of the 300b input stage of Spartacus 300 or better in order not to affect its sound. But we already use one of the most linear tubes there, so the choice was an inductively loaded heavy class-A differential stage canceling out the Libra’s 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 and the active unit. This keeps all mains AC and rectifier noise in a separate box while final regulation and filtering is still done next to each element in the amplification circuit. Everything is microprocessor controlled and the unit’s status is displayed on a large color LCD visible from your seat.
Libra should not be talked about but listened to.
Technical Specifications
Available Finishes
SILVER ANODIZED ALUMINUM
BLACK ANODIZED ALUMINUM
Downloads
OPERATING MANUAL
THRAX LIBRA BROCHURE
THRAX AUDIO BROCHURE
Reviews
Review by: Matej Isak
Review by: StereoNet