Upping a headphone amplifiers output impedance

Why do you want to increase impedance?  Don't you want a nice, low damping factor?  Also, what math are you using to show that a 600 Ohm headphone is difficult to drive?  I'm sure you know that impedance has nothing to so with an amp's power output and the sensitivity of the headphones, right?

Do you realize that solid state has characteristically low output impedance?  The only way I can think about increasing that would be with output transformers, but you'd probably run $200-$300 for just the transformers, not counting the rest of the amp.

I know you asked for solid state, but the only inexpensive high output impedance amp at HeadWize is the Kurt Strain OTL, with a stated output impedance of 500 Ohms.  You can get the power transformer for about $38, and you might be able to stay under $80 if you scrounge junked electronics and repurpose a case.

You can have high output impendace with a solid state design. You simply use a lower bias, no feedback or really low feedback and something else than an emitter follower (common base for example, as in Nelson Pass's Zen V9, 60ohm output impedance for 8ohms load).

Or a common emitter output, maybe mounted in some sort of push pull, like in singlepower square wave.

I think it is a good idea to match load and input imedance, damping factor of 1. This project is interesting, but doing something totally new and working great for 80$ is quite hard.

IEC standard output impedance, and the output impedance of most "600 ohm" outputs on studio gear is about 120 ohms. 600 ohms was the defacto choice for studio headphones for so long because you can plug them into the outputs of a mixer or pretty much any studio gear. 

Anyways, I would try Zo=120 ohms before much more. My experience with 250-ohm Beyers DT880's has been that they are actually quite sensative to output impedance. Perhaps even more so than other headphones.

Kudos to the OP for requesting that the amp be able to drive the headphone to a realistic SPL. I have a pet peeve about people who ask for an amp that can get 120db out of their headphones because (I dont know the reason actually). Quite a few amps can drive beyers to 104db. Even a basic Cmoy can do it as long as you have a 2*9V supply or better. The Pimeta from tangent may come in over budget, but is much nicer overall and will probably serve you better if you decide to get low impedance headphones down the road.

Quote:

Originally Posted by nikongod 

...Kudos to the OP for requesting that the amp be able to drive the headphone to a realistic SPL. I have a pet peeve about people who ask for an amp that can get 120db out of their headphones because (I dont know the reason actually). Quite a few amps can drive beyers to 104db. Even a basic Cmoy can do it as long as you have a 2*9V supply or better. The Pimeta from tangent may come in over budget, but is much nicer overall and will probably serve you better if you decide to get low impedance headphones down the road.

well how about the fact that dynamic transients in the audience can exceed 120 dB in some real life acoustic music events? - or is "sounding like the real thing" not enough of an argument for some wanting an "audiophile" experience from their gear?

my feeling is that people claiming 104 dB SPL clipping level is "enough" don't know what real music can sound like

... or simply haven't had their hearing shot by attending concerts after which your ears ring for 48 hours.  I totally enjoy music that sounds "like the real thing", especially when it's synthesized and digitally produced. :D  Had to put that in, don't mean to derail thread.

x2 on what nikongod said about Beyerdyanimcs and 120R output impedance, was nice to hear his amp with the 120R switch, it does sound like the DT880 was meant for it.

lower levels have their place - "background" music for all day listening should be 80 dB or less average and today even 12 dB peak to ave is considered a "dynamic" recording due the "loudness war"

but the point of background music is that you can tune it out while a symphony or big band jazz concert is meant to engage your full attention and live performances can ave 90+ dB SPL with > +20 dB peaks

amplified Rock or club music can be even higher  - but concerned audiophiles should probably wear ear protection if staying for a hour or more

even your local mall movie theater pumps out more than 104 dB peaks in the bass region - Dolby standard implies >105 dB SPL when you sum each of L,R with Mid and rear sides - before adding the +10 dB bass/lfe that in single driver headphones requires adding to peak L,R driver V

Maybe this link helps too. http://sound.westhost.com/project56.htm