Editor’s note: At the end of the MakerFaire in San Mateo, there is a “Bring a Hack Party “. That is where Ron Quan showed his tube headphone amplifier.
Here’s quick circuit for driving high fidelity headphones whose impedances are > 50 Ω .
The circuit uses one 12DS7 tube per channel with a regulated 12 volt DC supply at 2 amps or more. A switching 12 volt power supply (at > 20 kHz) worked fine for me.
My input audio source was a portable CD player with a volume control.
I chose these two headphones:
- Koss KTXPro1 (60 Ω )
- Sennheiser HD280 Professional (64 Ω )
Of course other headphones will work.
Stereo 12DS7 tube amplifier for headphones.
Schematic for one channel of the headphone amplifier.
Note that the 2200 uf capacitor’s “+” terminal can power the second channel amplifier. Also, the 150 Ω plate resistor should be 1/2 watt or more. All other resistors can be 1/4 watt, including the 4.7 Ω cathode resistor.
Also, the 100KΩ input resistor may be replaced with a 100KΩ potentiometer for controlling the volume.