Allow me to introduce an unusual hybrid headphone amplifier, which has been a playground of experiments right from its inception, sinking deep into the world of germanium transistors. Since the birth of our first prototype, I have tirelessly upgraded the circuit, collecting experience on transistor selection along the way.

Germanium transistors are unique things, they are more temperamental than their silicon brothers, but they possess a remarkable ability to breathe life into music, infusing it with an unmatched speed and easiness. They are quite gentle and dont like high temperatures, so you have to take care of properly designed output stage.

An advantage of the solid state output stage  is its ability to operate without the output transformer, a feature that simplifies the circuitry compared to traditional vacuum tubes.

In the base of this amplifier lies a single-ended output stage operating in Class A and using AD132 siemens pnp transistors.

The input stage, with a gain about 10, is fashioned using a 5687 tube in like SRPP configuration. You also can use E182CC with even higher gain. To power the input stage, I used a 5Y3 tube rectifier. The warm and rich sound produced by direct-heated tubes has won me over, and I use them wherever possible for many years,

The amplifier has  two switchable inputs and is equipped with a miniature fan to keep the output transistors temperature in check.

To avoid hum , I used the voltage stabilizers that also are based on germanium transistors.

Output Voltage:

  • 32 ohms: 3.5V RMS
  • 80 ohms: 7V RMS
  • 600 ohms: 8V RMS

At a 32-ohm load, the frequency response spans from 5Hz to 100kHz, with a mere 0.7 dB of deviation.

Update Hybrid headphones amplifier. A new top cover for better heat dissipation in class A.



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