> The gist of it: hook an OPA134 up to your headphones. Done.
No news. Sennheiser published plans for a 741/558 opamp booster for their 2,000 ohm phones. RCA used the uA709 op-amp as broadcast console can driver.
And everybody and his Chinese competition uses one of the NJR hi-current dual opamp chips for headphones. It works
> Anybody tried this one yet?
Who hasn't? www.headwize.com
has a forum, check out the DIY section.
> what is the point of a headphone amp between a portable cd/mp3/minidisc player and the headphones? Obviously they are all capable of an adequate volume...so what's the deal?
Many of them are not so good.
A particular problem was: in the Old Days (1999), many "good" headphones were 100-300 ohms, and would not suck large power from a 2-AA power circuit. 2-AA = 3VDC = 1Vrms or less than 10mW in hi-Z phones. At 88dB SPL/mW, that's under 98dB SPL peak and probably under 85dB SPL un-clipped speech/music. And 1Vrms from a 3V supply will tend to be un-clean, because of the low voltage and low available gain.
The need is less now. Many "good" phones exist in 32 ohm flavor. 1Vrms in 32 ohms is 30mW which is generally ample. But a few low-sensitivity phones (and some low-sensitivity users or high ambient background noise situations) need more.
My own interest is wall-power faultless phone amps which can beat the level of a live stage act (>115dB SPL) if only for a few seconds a night (WHAT???!). In hi-Z phones this can be >5Vrms; I use 24V rails. (This hot-box is a far cry from a cMoy mint-tin amp.)
> look at the TPA6120A2
Yes, telephone-line drivers and headphone drivers have the same historic roots, and this DSL crapola has forced insanely excellent line drivers on cheap chips.
And yet some geeks must roll-their-own. Headwize forum currently has a hyper-complicated brainstorm posted.