THRAX TERES Mk2 stereo power amp, £18,500

The Teres Stereo is Thrax’s space saving and cost effective entry point into it’s world of high performance separates amplification. The tonality and dimensionality of tubes delivered with might, authority and power. Teres employs a single-ended tube input stage loaded with a phase splitting transformer which then feeds two separate out of phase single-ended amplifiers. As only the first few watts are biased to Class A, Teres does not run ridiculously hot and the compact form factor and Thrax’s exemplary casework and build means an amplifier that suits UK homes very favourably. Extreme power, clear tone, unbridled dynamics and deeply impressive low level resolution.

  • Long-life input vacuum tube

  • Custom phase splitting transformer

  • Silicon carbide rectifiers

  • Shunt-regulated power supply for the tube stage

  • Solar cell bias of output stage

  • Microprocessor-controlled operation

  • Zero feedback

  • Special grade screened power transformer

  • JFET/MOSFET cascode output devices

  • Modular construction

  • Solid machined aluminum chassis

  • Stereo output stage implementation with dual mono drivers

Weight: 26kg
Dimensions 340x440x230mm
Power max. 500W 115/230V 50/60Hz
Max. input level 5.5V Rms
Output power 150W@3% /8Ohm 200W/4Ohm
Gain 16db
Input impedance 47k
Output impedance .4 Ohm
Signal to Noise 114db
Frequency responce 20-20,000Hz +/- 1db

Teres uses a single-ended tube input stage loaded with a phase splitting transformer. The transformer then feeds two separate out of phase single-ended amplifiers for output. The tube handles all the voltage gain needed giving the overall sonic character with high content of second harmonic. It is based on the Dionysos gain stage using a new generation of our choke-rectified shunt-regulated power supply providing a noise-free operating point, clear tone and unbelievable dynamics with zero modulation of the noise foor.

The output stage’s power JFET cascodes form a bridge that when unbalanced by the input signal via the interstage transformer windings restores balance by adjusting their current conduction through the load. The two output stages actually enclose the load in their control loops and try to correct each-others errors reducing the distortion to insignificant amounts, leaving the “character” of the input stage untouched. Those Fet’s provide no signal gain, they merely satisfy the load’s hunger for current.

To reduce the amount of heat generated the amplifier is biased so only the first few watts are in true class A. Music has a crest factor of 10 on average. This means that most of the time we listen at 1/10th of the peak levels. For most users this translates to under 5W. Peaks can reach over 100 watts during playback, but only for a few milliseconds. For those peaks the amplifier switches to class B using only one leg of the output stage capable to deliver up to 150W/8ohm and 250W/4ohm.  The result is an amplifier capable of extreme power while delivering exquisite smoothness and low-level resolution.

The driver stage being isolated by the interstage transformer is not influenced in any way by the output stage operation maintaining tone, colour and resolution at all power levels and loads. Having the output stages floating around the load prompted for the use of a unique biasing technique powered by solar cells. This was the quietest galvanic isolated power we could come up with. Using opto-electrical conversion we control the bias by adjusting light intensity in the control circuit. Teres is an example of modern technology solving age-old problems allowing us to go a step beyond what was possible before.  The exquisite aluminum finish adds to the presentation of a solid block of metal.

REVIEWS AND FURTHER READING

Teres Brochure – TBA
Teres Operating Manual – TBA
Thrax Audio Brochure

THRAX AUDIO WEBSITE