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Yes I have seen this. But which amps that "don't break the bank" are available with 0 ohm output impedance?
I see O2, Magni3... Basically outside of that there aren't many 0 ohm output impedance amps period that are under $500... and even at $500 there aren't many.
What I have found is most are $800 or $1000+ often with no measurements at all....
I really want an Amp that is just like the A30 but with a proper output impedance.
JDS EL Amp - and most amps derived from the lme49600 reference design (AN-1768 http://www.ti.com/lit/ug/snaa052a/snaa052a.pdf) - should meet the near-0Ω criterion, as for that matter would most generic implementations of IC opamps intended to drive headphones. Oddly few of them around for a low price, granted, but they do exist, and when you expand tolerance to an ohm or two (which is unlikely to cause substantial frequency response deviation outside of multi-driver IEMs with very low impedance armatures) then many of the cheaper amps and DAC-amps become viable (E10K, for example, although due to its voltage restrictions that's not much of an amp if you really need high output).
At the cheapest, even a simple single-stage "C.Moy"-style DIY project will result in a low output impedance with stable operation if the right opamp was used - heck, the 4556 from the O2 would work (even when sold from dubious Chinese eBay storefronts with even more dubious design premises http://nwavguy.blogspot.com/2011/07/cmoy-with-gain.html ) , although it's a bit nonlinear for my taste (even if you are unlikely to hear the difference). Really, it's more confusing that so many "high-end" designs have such high output impedance...
If you want to know what really confuses me, though, it's the fact that nobody seems to have made some of the cheap options for making a simple, linear headamp into a very cheap box - the OPA1622, for example, is an essentially ideal single-chip solution for a simple headphone amplifier, but I don't know of any cheap boxes I can buy it in with preconfigured gain, some input filtering, and a power supply on the cheap, even though AFAIK it costs similarly to the TPA6120A2 in volume. Perhaps it's just too new and some Chinese company (perhaps Topping ) will make me a happy man by making a $50 box with a 1622 in it that I can recommend people.
What I have used before is the UE Buffer jack, and I have wondered if that really does "lower" the output impedance or if it doesn't, if its possible to build such a device that is simple and can lower the output impedance by say presenting the amp with a 100 ohm or more load and then having its own output of 1 or less.
The buffer jack presents itself to simply be a resistor voltage divider, to my understanding? If so, it would work - with the obvious caveat of sacrificing some voltage sensitivity, although I suspect in the case of sensitive IEMs that's more a feature than a bug. Sony did something similar on their old open-air designs using a pair of 22 ohm resistors, I recall, directly soldered onto the driver terminals, and for the same purpose: decreasing the change in frequency response from a high source resistance.
Edit: Wow, they want $280 for the EL Amp? That's...a bit steep, to be honest. I'd assumed it'd be closer to half the Element's price, given that it's close to half the Element. Shame FiiO never used the LME49600 combo in a desktop amp to my knowledge - the mobile amp based on it, the E12, was quite good - and wonderfully cheap - but for some reason their desktop stuff still uses the TPA6120A2 last I checked.
2 Edit 2 Furious: Actually, the E12 and the A5, its direct successor, are probably a quite reasonable options if the A5 still performs like the E12 did when Tyll Hertsens measured it (it is identified as "Fiio Mont Blanc here https://www.innerfidelity.com/images/AllAmpsJuly2013.pdf in a PDF that can only be found via this news post https://www.innerfidelity.com/content/innerfidelity-july-2013-update - I really love Innerfidelity, but I reeeaaaaally hate its organization). It has a very long battery life and can to my knowledge be used while charging, and the E12 measured quite well. I'm a little skeptical of the boutique opamps in the A5, but FiiO seem to be pretty competent, and I hope that they didn't mess with a good thing...
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