New to headphone amps --- I'm wondering .....

Interesting but you guys are a bit over my head. What does this suggest would be the right amp -- or type of amp -- to match the AKG 545s. My budget is around $300 give or take a bit. Reading the forums at hed fi left me a bit overwhelmed with options. Are you guys suggesting that these are esp difficult headphones to drive? They don't seem to require much power. What do y'all recommend?

Thanks ...

Hmmm, I just noticed that per this spec sheet the 97 db/V sensitivity spec shown at the AKG website is incorrect, big-time!

Per the spec sheet, the figure is 97 db/1mw, which seems a lot more sensible. So 99 db would be produced in response to an input of 1.585 mw, not 50 mw (10 x log(1.585/1) = 2 db).

So the speakers I described would require 40/0.001585 = 25237 times as much power to produce the same 99 db SPL at a 10 foot listening distance. And the 50 mw maximum power rating of the headphones would correspond to an SPL of 114 db.

Regards,
-- Al

Mechans, as Mulveling indicated my calculations are consistent with the published specs, shown near the bottom of this page. As he points out, though, it certainly seems possible that the max power handling number reflects how much power the headphones are rated to handle continuously, and that they may be able to handle considerably more on brief musical peaks. And/or perhaps that spec is very conservative, and has a lot of margin built into it.

Either way, though, the relation I described between power requirements for the phones and for the typical speakers I described remains valid, assuming the sensitivity and impedance specs are accurate.

FYI, the derivation of the 99 db figure is as follows:

The sensitivity spec for the phones is 97 db/V, which means that 1 volt in results in a 97 db SPL. Impedance is 32 ohms. 1 volt into a 32 ohm resistive load corresponds to 31.25 milliwatts (mw), based on (Vsquared/R). The 50 mw maximum power spec is approximately 2 db greater than 31.25 (based on 10 x log(50/31.25)). 97 db + 2 db = 99 db.

Regards,
-- Al

Mechans -- as far as the AKG 545's specs go, Almarg's 97dB/99dB calculations are correct. And yes, I too am surprised that they are so low. Potential hearing damage issues aside, a $300 headphone that is limited to 99dB max (as spec'd, which does not distinguish peak vs. continuous) @50mW is rather low. I vaguely recall my Sennheiser HD600/650 being rated at a max near 120dB.

Almarg,Are you sure the power is so low. Most of the headphone amps I know about put out around 0.5 wpc. (there is a wide range but I am suggesting this number just for scale)

There is little discussion needed...get a dedicated amp for your headphones

Lots of good points have been made above. I would particularly emphasize three of them, and add a fourth.

1)

02-10-14: Doggiehowser
The relative amount of power needed to drive cans (even something as difficult as a pair of Hifiman HE6) is a mere pittance compared to a regular pair of speakers so you don't have to pay for more power. Just a small amount of high quality ones.

To add some quantitative perspective, the maximum amount of power your 545s are rated to be able to handle is 0.05 watts. And in response to that maximum input power they will produce a very loud 99 db of volume. In comparison, a pair of box-type (non-planar) speakers rated at 90 db/1 watt/1 meter will require about 40 watts, or 800 times as much power, to produce the same volume at a typical listening distance of around 10 feet.

2)

02-15-14: Mulveling
In your case, by running from tape-out you're almost certainly creating an impedance mismatch ....

The tape outputs (as well as the main outputs) of your Exotik preamp are spec'd as having an output impedance of 330 ohms. That is about 10 times greater than the 32 ohm impedance of your headphones. For a line-level interface, ideally the load impedance should be at least 10 times greater than source impedance (at all audible frequencies); in this case it is 10 times less.

3)As was noted you apparently have no means of adjusting headphone volume.

4)After looking at the manual for the preamp I can't tell for sure whether or not the tape outputs are driven by a buffer stage which isolates them from the main signal path. Many and perhaps most preamps do not provide a separate buffer stage for their tape outputs, although I suspect after looking at the manual that yours does. If it does not, however, I wouldn't be surprised if applying the 32 ohm impedance of the headphones to the tape outputs adversely affects the sound you hear through your speakers (just while the headphones are connected, of course; I would not expect any damage to occur, that might affect sonics when they are not connected).

A dedicated headphone amp, connected to the tape outputs, would resolve all of those issues.

Regards,
-- Al

In your case, by running from tape-out you're almost certainly creating an impedance mismatch that is rolling off your bass response big-time, and in general wreaking havoc on the net frequency response. The effect is exacerbated with headphones of lower impedance. The sound can be perceived as detailed or even "airy" this way, but it is not accurate. I've heard that result a few times, with a few different causes. If you're like me you'll tire of it and start craving a firm bass anchor to your music.

A properly engineered headphone amp will have a low enough output impedance to match with (most) headphones, and should thus yield a frequency response in keeping with the designer's intentions. Even those headphone amps with a higher output impedance (OTL tube amps) are usually voiced to end up sounding fantastic with certain headphones (e.g. many of those Singlepower amps and 300-ohm Sennheisers, or really almost anything before driven to clipping-- the Singlepowers should't sound nearly as good as they do, but they do).

In other cases, where you may have a headphone jack provided on say a $4K integrated, then you have to consider what's actually behind the headphone jack. What makes for a great line stage circuit is usually going to have too high an output impedance for most headphones...and rather than compromise the main circuit, it's common to see a crappy little opamp based headphone amp behind that jack. Even gear that boasts "discrete" headphone circuitry usually won't invest the right real estate, parts, and engineering to get it right (when headphones are an afterthought for most buyers of high-end speaker gear). Hence, a properly engineered $500 headphone amp may yield a much more pleasing result.

Now that's not to say that even most $600 headphone amps will sound particularly good, but it should be possible to find one (especially in the used market) for that price that will sound great. I think I remember buying an old used Headamp Gilmore Reference for like $650? That thing was awesome. And an old maxed-out PPA set me back a whopping $200 and can make other amps in the $1000 new range sound like garbage by comparison. If you're a gambling man, Singlepowers (with a rightfully deserved bad reputation thanks to their creator and their potential hazards) represent some of the most pleasing sounding amps around at any price (though a few do sound not so great...lots of unit-to-unit variation). That said, I'm not familiar with the newer crop of headphone amps from the last several years.

All I can say is that I've never had an amp that compared to a dedicated headphone amp. The only amp I've heard of that could equal or best a dedicated headphone amp is a Cary SLI 80 and I've never heard one. My k702's with my old Rogue Cronus Magnum were awful. The same cans with my Schitt Lyr are amazing. You should check out Woo Audio as well.

I rarely listen to headphones (except when recording of course) but I run a little 12AU7 based Chinese tube headphone amp from the extra outputs of my preamp...makes it remote controllable (unlike a tape out, which my preamp doesn't have), and it sounds great (I did upgrade the tube)...amazing since the amp cost about 50 bucks and is by far the least expensive component in my rig. Since my head is mostly empty I do get some echo, but I ignore that.

Definitely getting a headphone amp is a must for your needs, you have more control over your headphones and nothing can beat the quality of a dedicated unit.

Take a look at Burson audio Soloist SL.

"But can anyone explain why a headphone amp that costs a fraction of the cost of one's much more costly main rig would sound better?"

There are no crossovers in headphones. You can obtain high quality SET Class A power headphone amps relatively inexpensively. There are no room interactions for headphones, thus no expensive room treatments. There are no requirements for speaker cables. No requirements for preamp.

How are you controlling the volume then?

I find the headfi provides some advantages over a normal hifi system.

The relative amount of power needed to drive cans (even something as difficult as a pair of Hifiman HE6) is a mere pittance compared to a regular pair of speakers so you don't have to pay for more power. Just a small amount of high quality ones.

Two, hifi systems are affected a lot by the room the system is in. You can do room EQ or use copious amounts of room treatment but there are limits to what can be achieved. On a good set of cans, the room is out of the equation, as the sound goes from the transducers to your ears directly. No reflected sound, no diffused sound. You can often pick up far more detail in a good set of cans that is hard to discern even on speaker systems that are multiples more in cost.

The downsides to me are in the way soundstage is reproduced. You can experience wider sound stages in headfi with the right gear but fundamentally, the main problem is that the centre of the soundstage is between your ears and inside your head. That can sound unnatural. In a hifi system, the sound is in front of you, with a good amount of depth that mimic a live performance, almost.

There are headphones like the Sennheiser HD800 which angle the drivers somewhat and can create an effect of the soundstage outside your head but it is still a little subtle and doesn't beat even a cheap pair of speakers in creating that deep soundstage.

As for head amps, like with things hifi, it's always best to listen and audition. Some amps have good synergies with some headphones so it's always best to test if the combo works in your system. I found my Schiit Lyr for instance to be a good match for the HD800 and the HE6 but was a tad noisy with my LCD3.

I think Schiit headphone amps are hard to beat for the price and features.

Thanks. I get the sense that many people find that headphone amps make major improvements. But can anyone explain why a headphone amp that costs a fraction of the cost of one's much more costly main rig would sound better?

I'm running RCA cables into a relatively cheap RCA to mini-plug adapter, that then goes to my headphones. I imagine the cheap adapter isn't helping, esp compared the the Stereovox interconnects I use to connect my the components in my main rig.

How are you getting the signal from Tape Out to the headphones?

I use a dedicated headphone amp now out of necessity but also did with a $12K main rig. This particular headphone amp is a tube amp made by the disgraced manufacturer SinglePower (but it still sound great to me).
I would refer you to the HedFi.Org web site for all the information you seek on headphones and the amps to power them.
My own experience is that good headphones sound much better with a dedicated amp. You may find yourself witth more than one pair of headphones if you follow this path, I did.