Saturday, February 20, 2010

Headphone amplifier

Nothing puts you closer to the music than headphones.
However, to reach this intimacy, good headphones must be driven with appropriate headphone amp.

Most of the people do not like headphone listening. Either because headphones are uncomfortable to wear for them, or most of the time they do not like the sound. And I do not blame them. Most of headphone outputs suck. CD players and cassette decks usually have outputs without volume attenuator and even if they have, the sound is just awful.
But it does not have to be that way. Theoretically headphones should allow you to be closer to the music, more intimate, not disturbed by outside noises. Furthermore, it should be easier to cover the whole frequency spectra with one voice coil, no crossovers,no phase shifts; not influenced by room acoustics, just the recorded sound; should be easy to drive, just a couple of milliwatts...
Why it is not that way?
As I said, to reach this intimacy, good headphones must be driven with appropriate headphone amp.
When it come to headphones, I settled with Sennheiser's HD580 and Grado's SR325. I am not saying that there are no better cans, but these are exceptionaly good. They are just like jin and jang. Two different wolds. Grados are neutral, well balanced, deep powerful bass is combined with extended heights, clean and precise sound. Very dynamic. Their 32 ohm resistance can be a problem for high output impedance tube amps. But I use them often, sometimes I have a taste just for this precise presentation. Sennheisers on the other hand are lighter sounding, nice soft heights, generally more lush and sweeter sounding. Might be too sweet and light with some tube amps. Very pleasant to wear unlike Grados.
Headphone amps?
I have Musical Fidelity's X-Cans, excelent headphone amp. Plus I built a couple of headphone amps myself. Each amp sounds differently. As well as each headphones. So there is a lot of combinations to explore.

This tube headphone amplifier is a combination of Eric Barbour's and Kurt Strain's constant current/mu follower. Amp uses two 6SN7 tubes per side. I tried various power supply versions, solid state rectifier for high voltage and rectified and filtered heaters worked best. Sound of this headphone amp easily beats Musical Fidelity's X-Cans. It is warm, soft, euphoric and clean and dynamic at the same time. I bet it has a lot of second harmonic distortion, just what I desire. I have no way to measure it. And I do not care how it measures, it just sounds great. Never heard anything more euphoric, pure listening bliss!

Update...I have recently converted two tube amplifiers into headphone listening as well, besides the speakers. Using direct signal from the tube amp to power headphones is wrong, complete mismatch of impedance and sensitivity. Transformer coupled output has secondary winding designed to see certain impedance, usually 4 to 16 ohm, which is expected to be on the output for proper operation. Plugging 150-300 ohm headphones will result in increased noise, hiss, hum and may damage headphones with too high signal, and even worse, your hearing. Headphones are just too sensitive and require only tens of miliwatts. If you have headphones with 16 ohms, which is just wrong move on the side of manufacturer of these headphones, because plugging of these to normal jack in the mp3 player or cd player powered by OPA, will result in the OPA overload, be careful, as you may have too much signal to damage the headphones and your hearing, as said above. Easy solution is voltage divider, see picture. You present amplifier with proper impedance and take small part of the signal to power your headphones.
If you have capacitor coupled OTL amplifier like Transcendent SEOTL, you may find other resistor values to work better than for transformer coupled amp, so some experimentation is required. Below in the picture is what worked for me. I do not understand why Bruce suggests to wire headphones directly to this amp, doesn't he listen before he gives and advice? Try both ways, directly, and you will have buzz, hiss and too much sensitivity issue; and with simple voltage divider, and you get pure listening bliss to one of the best sounding amplifiers...good luck!