Posted on Monday, July 4, 2011 • Category: Headphone Amplifiers
Here's a simple to build hybrid tube headphone amplifier built around 12AU7 / ECC82 vacuum tube. I have always been intrigued by tube amplifiers, but most DIY kits are very expensive and use very high voltage. So I decided to build an amplifier that would be inexpensive and had the least amount of parts necessary to drive a pair of 32 ohm Grado headphones.
Having built several YAHA amps based on the fa-schmidt design, and a Szekeres Mosfet follower I wondered how the two would sound together. So I built the schematic into TINA-TI, a free spice based program to test circuits before the build, and the results were remarkable. Nearly 20dB of gain across 20Hz-100kHz from a 13VDC power supply.
As you see in the schematic and parts list, there are less than 30 discrete components and most DIY'ers will have them as spares from other builds. I chose the 12AU7 / ECC82 vacuum tube because it can be driven with low voltage and the filament voltage is 12.6 volts, so there is no need to regulate the voltage any further. I used 1/4W resistors in the first stage and 2W in the second. The 2W resistors may be overkill but I did not want to change them later. The 20ohm resistor must be a minimum of 5W and do not use wire wound, as the inductive characteristics will distort the response curve.
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