The T4 dierential hybrid parafeed headphone amplier, custom as-
sembled by Beezar Audio, was created by ECP Audio. The T4 continues
in the tradition of its predecessor, the ECP Audio/Beezar Torpedo III. Its
circuit and conguration are totally unique in the world of headphone
audio. The T4 combines tubes with a fully dierential solid-state out-
put, feeding into custom-manufactured Lundahl output transformers
for the nest in single-ended, zero-feedback output from a headphone
amplier. The result is perhaps the nest tube headphone amplier
available anywhere at this price point.
Amplier Design Description
INTRODUCTION
The tubes are congured in a long-tail pair that results in a fully dier-
ential output. From there, a fully dierential solid-state buer is used,
terminating in output transformers congured into a parafeed ar-
rangement, where the dierential signal is combined back into a single
ended connection at the headphone jack. Because of the fully dier-
ential circuit, common mode distortion is fully cancelled out. At the
same time, the solid-state buer output after the tubes results in more
power than would be available from the tubes themselves. The output
transformers assist with this, ensuring that ample current and voltage
are available, regardless of the impedance of the load.
ECP Audio designed the T4 headphone amplier to utilize the ubiq-
uitous 12A*7 audio tube family. Specically, the T4 is designed for the
12AY7 or 12AT7 tube, but others can be used that meet the general
12A[T, U, V, X, Y, Z]7 tube specications. There are many, many other
tube types that will work, too. Refer to the tube section of this manual
for a list.
The T4 includes a “Z”switch that allows switching between low and
high-impedance loads (75 to 300 ohms). This switch may be thrown at
any time - even while music is playing and headphones are plugged in.
Note also that with a true, output-transformer-coupled amp, there is
no need for any kind of power-on or power-o headphone protection.
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