LIBRA

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DIFFERENTIAL BALANCED 300B TUBE PREAMPLIFIER

Statement differential balanced 300B tube preamplifier of the 21st century.

Features

Post amplification volume control for lowest noise
Modular construction
External dual mono power supp-ly with choke input rectifier for lowest switching noise
Programmable Balanced Tape loop
Stepped volume control for perfect repeatability of level settings
Interlocking solid aluminum chassis
RCA and XLR inputs with adjustable sensitivity controls
Highest quality long life 300B tubes
Single gain stage
Dual balanced output for bi-amping with offset adjustment

Home Theatre bypass feature for integration in Home Cinema systems
Microprocessor-controlled opera-tion for safety
Special filament heating circuit for harmonic richness and tube protection
Current sourced regulator for stable power-allowing explosive dynamics and tonal purity
DC-coupled input and output for ultimate transparency
Balanced differential topology for noise immunity & subtle dynamics
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


Weight:	Main 26kg, power 34kg
Dimensions	430x450x150mm
Power	80W 115/230V 50/60Hz
Max. input level	5V Rms
Max Output level	10V Rms
Gain	+12db
Input impedance	90k Ohm
Output impedance	80 Ohm
Signal to Noise	90db
Frequency responce	20-20,000Hz +/- 1db