Originally Posted by WilCox
Originally Posted by vlach
That's an incorrect assumption. I for one listen to very high quality recordings, mostly jazz and the Leck does a superb job driving my HD800 'WELL'.
+1. Same here. I have a large library of classical and jazz 96/24 FLAC and the Leckerton reproduces them beautifully. You can't draw assumptions simply by taking numbers from a spec sheet and plugging them into an equation -- ultimately, you have to listen.
of course we can. what makes it hard is the lack of enough specs.
the given sensi for a headphone has been obtained by feeding the headphone with 1mw and measuring the output. so you do know for a fact that if you put 1mw into the headphone you can get the given loudness.
then the question is pretty much to know how loud you're listening to and you can tell what the amp will need to be able to deliver. it's not magic.
with only the specs @1khz you won't be able to tell the all story, but nowadays you can find impedance graphs to further know what will happen and estimate the needs at any frequency.
another unknown is the amp itself,as the specs given are also for 1khz so there may be small differences at other frequencies. but that's the reason why we go a little over the top when we look at the needed loudness, and usually seek numbers for the headphone to play up to 115 or 120db. that accounts for the peaks(because felt loudness is lower, at least for dynamic music), and a little more headroom for unknowns, like when the manufacturer write 50ohm, but the model you end up with is really 47ohm or something like that.
but if the measurements are good and we have a good deal of them, then you will know exactly how to drive well a headphone at a given loudness or when it will start to distort(well exactly when it will go over 1%, but usually when the amp reaches that value it goes a lot higher very soon after when you keep pushing).
for the hd800 I read 102db/1Vrms and 300ohm from the official specs.
for practical number to see if we're good, I take innerfidelit's pdf http://www.innerfidelity.com/images/SennheiserHD800.pdf
at the bottom you see that he made measurements for voltage and power to get 90db@1khz.
to get Tylls values @90db the hd800 he had would be closer to something like a sensi of 102.3db/1Vrms and 360ohm. the sensi is really close to given specs, no problem there. and if you look at the impedance graph on the PDF, more like ... I don't know, maybe 360 or 365ohm? how nice of the actual measured specs to go with the expected number from calculus. as if they were actually meaningful.
even with 102db and 300ohm like sennheiser said, we would be wrong by 0.3db in our estimation @90db compared to Tyll's result. not a drama and that shows how reliable those numbers are even when not perfectly right(it works well simply because electricity is a known science).
now what it tells us is that to drive the hd800 up to 90db we need 0.16mw and 0.24volt.
from the leckerton we get 40mw as max power (below 1%distortion) into 300ohm, so obviously we're great and people who don't listen to music with any peaks above 90db are golden with that combo.
now to reach the usual 115db we ask for when we look if an amp can be good for every uses with the headphone(as I explained above). we end up needing 51mw for Tyll's hd800, and 66.5mw for a hd800 with the actual sennheiser's specs of 102db and 300ohm.
both failing by a little margin when fed by the leckerton and his 40mw into 300ohm(again for the provided op amp measurements). the reason why you feel like it's ok can be simply that you don't listen so loud, or that you don't notice the few peaks being slightly distorted.
in this particular case, the amp would fail by less than 3db so it's as good as calling it a pass.
and for the voltage, leckerton says +18db, so if I'm not mistaken, as long as the source feeding the amp has more than 0.6v, the HD800 will go loud enough in all expected situations(listening real loud to real dynamic music).
now the unknown:
the hd800 can reach about 640ohm @100hz, and we don't know what max power the leckerton can feed into 640ohm. so while we would need a good deal less than into 300ohm, it rises a doubt. a doubt that would be eased up if our 115db estimation had been passed with flying colors. that's what headroom is for, to ease up our mind on small maybes.
also bob kats was saying 2weeks ago that to him having more headroom often meant better sound(it was a subjective opinion for that matter, but he seemed to hold firm to it). so if you trust his opinion, you may want to do better than "almost good".
as for the LCD2 I checked rapidly, and the answer is: it depends on the damn headphone.
specs are all over the place depending on revisions. so I took the rev2 on innerfidelity(cause that's what schoppy has) and looked at what specs the headphone he measured really had. I end up with 58ohm and a sensi of about 90.6db@1mw. anyway for our usual 115db loud into the headphone, that's 275mw needed. again I don't know what gives with the opa627, but what we get from the leckerton webpage gives a fail into 62ohm for both AD op amps that are closer to 100mw. and with a relatively low impedance, the question of having enough current comes up too(when we pretty much dont care or the hd800).
but once again it depends on how loud the user goes, and how dynamic the music is. when what feels like 90db may very well be 93db with the latest justin bieber, the actual peaks could reach a good 15db higher at times with some classical pieces. so for those who sometimes like to listen louder for a song or just a passage, it's very possible that the leckerton will fail.
and if you remember it's nothing more than what headwhacker had been saying the all time, except that to him we should take 120db to make our estimations, making the values to reach even harder for the amp.
and as I said I know for a fact that I never use above 100/105db peaks at home(measured the outpgoing voltage for a test tone with the source's volume set from listening to music pretty much the loudest I thought I would ever use with a few different tracks. it's a very quiet room in a very quiet village and I always disliked loud sounds. but I know I'm not everybody so I don't say a pairing is ok when it's only ok for my use. I say it's ok when the numbers show that nobody will be able to push the amp too far(so 115 or 120db). and if I say it's ok for me I would add how loud I tend to listen to the music, as loudness is most of the driving problem with many headphones.