Thrax Audio’s TERES: A TRANSFORMER COUPLED HYBRID POWER AMPLIFIER
30th March 2017
This 120W design is based upon single-ended valve input, stage-loaded with a phase splitting transformer controlling two separate single ended, out of phase, amplifiers
The Siemens C3g valve (with a battery bias for low noise), according to the company, handles all the voltage gain needed and uses, “…a new generation or our choke-rectified, shunt-regulated power supply providing a stable noise-free operating point.” The CR2032 3V lithium battery bias lasts for around five years before a battery replacement is required, incidentally.
The output stages power JFET cascodes. The two output stages actually enclose the load in their control loops and try to correct each-other’s errors, reducing the distortion. Leaving only the “character” of the input stage.
To reduce the amount of heat generated, the amplifier is biased so only the first few watts are in true Class A. Peaks can reach over 100W during playback, but only for few milliseconds. For those peaks the amplifier switches to Class B using only one leg of the output stage.
“The driver stage is isolated by the interstage transformer and is not influenced in any way by the output stage,” said the company. “Having the output stages floating around the load prompted 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.”
Spanning 340 x 400 x 230 mm, it weighs in at 25kg. To learn more about the company, click HERE .