I listen to music on headphones a lot at work, and my source is almost always a CD/DVD-A/SACD player (Denon DVD-2910). Since it doesn’t have a headphone driver, I need something to power my various cans (1, 2, 3). In the past, I designed a tube-based headphone amp but frankly while it’s nice for nostalgia’s sake I’m not interested in “tube sound” (a.k.a. “a lot of even-harmonic distortion”), so why go to the trouble and expense? Let’s get more modern, cheaper, and a lot higher performance. (The name Gilberd is after William Gilberd, an early figure in electrical engineering.)
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I have a couple in my spares box and really should get around to building something.
I have wanted to build a headphone amplifier for quite a while. I just cannot settle on a spec. My best headphones are Sennheiser HD424. They are very comfortable for long sessions and they sound very good to me. Most headphone outputs will not drive them well because they are 2000 ohm impedance. The other issue is that they are open back and don’t provide ambient sound isolation. All the other headphones that I have are ~$20 JVC, Sennheiser, Maxell, Sony, etc. Some are earbuds, which I prefer for working and the others are closed back. They are all lower impedance (some as low as 16 ohms. I have been unable to develop a design that suits me that can drive this range of impedance without running into problem. I also have read that there should be a 120 ohm source impedance.
"The IEC 61938 international standard specifies that headphones should be driven by a 120 ohm source – regardless of the impedance of the headphones themselves." <http://gilmore2.chem.northwestern.edu/faqs.htm> I have not read the standard so I don’t know what the context is.
This may minimize the impedance range that I need to drive. It also eliminates the need for short circuit protection.