Set me straight on headphone amplifiers...

[shadyJ]

Headphones are not my area of expertise, so I have a question: how many headphones really need separate amplifiers? I have never had the problem of an amplifier not getting the headphones loud enough for my tastes, from any generic headphone jack I have ever used. I can maybe see a headphone with a very erratic impedance profile benefiting from robust amplification, if that impedance profile can actually affect frequency response from so-so amplifiers, but that would seem to be more of an issue of a problematic headphone rather than necessitating a separate headphone amplifier. I can see getting a DAC for headphones since some of the generic jacks I have used have had electric noise leak into the signal.

Are there so many high-resistance and low-sensitivity headphones out there that typical jacks do not offer enough amplification and separate headphone amps are a big thing? Something else I have noticed in recent years is AVRs, integrated amplifiers, USB sound interfaces for computers, USB DACs for PCs, is that they are starting to hype high-quality built-in headphone jacks as a feature, so this would seem to lessen the need for separate headphone amplifiers even more so.

 

[cel4145]

Depends on the headphones and what you are trying to drive them with. Check out Innerfidelity's headphone measurements: http://www.innerfidelity.com/headphone-measurements. You'll see Volt RMS and wattage ratings needed to reach 90db at the end of the measurement documents. The most difficult to drive headphones tends to be open ones. The highest sensitivity/easiest to drive are IEMS, with a much bigger range of difference between those than you'll see among speaker sensitivity/efficiency.

Also, there is this consideration about low output impedance which ties into your point about variance in headphone output impedance: http://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html. AVRs/integrated amps typically do not have very low minimum output impedance. They are what's problematic, not so much the headphones. For example, my AKG K7XX sound better out of my little Fiio E12 amp plugged into my AVR headphone jack than straight off the jack itself.

Then if you want to add +8 or +10 db of bass boost, for example, you may need amplification when you didn't otherwise need it. After all, headphones are doing double duty as speaker and subwoofer and as such, with bass heavy music and bass boost, you may benefit from more power than in other listening situations.

But yes. I would agree that headphone enthusiasts, on average, are a little too focused on more power for power's sake without often deriving real benefits, and so the market is feeding that and reinforcing it. I just saw in another forum saying someone recommending a 5000mW amplifier with the Sennheiser HD600 was needed over an AVR, even though their sensitivity rating tells us that they can reach almost 120db with less than 200mw of power.

 

[tyhjaarpa]

There are quite many headphones that work without separate amplifier but will highly benefit from it. I personally have Sennheiser HD600 for example, they can be played with my phone and they sound fine but when I hook them in my AVR headphone out I get more bass and more detailed sound. I would say that pretty much any headphone can be played without amp but most of them will benefit from amplification. How ever if you have low impedance headphones then you will benefit less from amplification as they are easier to drive. Headphones with impedance of 50 Ohm or less should work really well without amplification, if your impedance is over 50 Ohm then you might want amplifier to pair with them to get best out of them.

 

[Boerd]

My (subjective) experience is that the iphone has enough juice for most headphones. The iphone is also very clean, in fact cleaner than many dac/amp combinations (see: http://www.kenrockwell.com/apple/iphone-6-plus.htm#measurements for example).
In general you won't need much power from a portable dac/amp. What you should look for is a clean, well measuring amp / dac (if you want something else than an iphone).
The reason I bought a Chord Mojo is to use it as an external card for my Dell XPS 12 (no fans - no noise) and enjoy my 200GB+ collection while using JRiver on a laptop.

 

[slipperybidness]

Many headphone amps just use an OpAmp IC, no need for a true Power Amp (IC or other). If I use a dedicated headphone amp, then I use my DIY CMOY design that operates off a 9V battery.

Also, most AVRs and Pre/Pros don't have a true dedicated headphone amp. Most of the time it is attenuated output from "some other part of the signal chain"--I can't remember the usual circuit topology off the top of my head, but I can remind myself when I get a chance.

My USP-1 has a "headphone output" and not a "true dedicated headphone amp", and I will say that I don't really hear a difference between my USP-1 and my DIY CMOY.

 

[shadyJ]

Thanks for the responses guys, I suppose I could have googled the answer, but I would rather have Audioholics poster's take on it instead of having to wade through a bunch of audiophile nonsense.

 

[lovinthehd]

Was wondering why you needed to ask since you seem to have a pretty solid handle on speaker based audio....but know what you mean, am not a headphone guy but if I were thinking of becoming one a thread like this would be one of the questions I'd have based on comments I've read.

The one pair of headphones I have had for eons (Denon AHD210) works well with all the gear I've ever tried it with, with maybe the exception of my phone being a bit weak on the volume side and was a common complaint with the analog output of that phone (and my purpose was more for connecting to my truck stereo or other analog gear than using headphones, though the phone would still deliver sufficient volume, just not extreme volume which I shouldn't reallly do anymore anyways).

 

[jmalecki05]

In general, if you headphones are greater than 50 ohm, then a headphone amplifier will increase loudness without sacrificing clarity. Audio players are rated for how many ohms they can drive (e.g. the Fiio X5 will drive up to 300 ohm, but I only tested with my 50 ohm Sennheiser HD 598). Headphones are rated as well.

 

[Boerd]

I have a Beyer DT 880 at 600ohms and the iPhone can drive them very loud. Same for the Sennheiser HD 650 - loud and clear. Read the sensitivity for your headphones and you will see you need very little power to get to 90db which is loud enough.
http://www.innerfidelity.com/headphone-measurements
HD 650 needs 0.13mw (0.00013 Watts) to play at 90 db. An iPhone can drive them at loud levels without clipping.
http://www.kenrockwell.com/apple/iphone-6-plus.htm#measurements

 

[JRT3]

I replaced my Emotiva a-100 mini-X 50 Wpc amp with a new model, the Emotiva A-100 BASX amp - because of it's s/n ratio (110 dB!) and included headphone jack and circuitry. They employ a 220 Ohm 5W resistor in series with the essentially zero output impedance speaker output from the 50 Wpc amplifier, cutting off the speakers when the 'phones are plugged in. That is pretty standard for AVR & stereo amps & receivers - even to the choice of the current limiting resistor. As the resistor sets the headphone output impedance to ~220 Ohms, it's a reasonably good match to my Koss Pro-4AA, both rebuilt old & new alike and their 260/250 Ohm impedance, as well as my old Sony MDR V6's (~90 Ohms). The new amp has higher current needing headphones in mind, too - it includes jumpers to jump across those 220 Ohm resistors, placing the speaker output directly across the headphones. Not for me... if I want to see smoke around my ears, all I need is to listen to a politician. Still, the high s/n ratio would mean you couldn't likely hear any hiss or hum during low passages - still, I am happy with it as-is. It just sounds better than my Onkyo C-7030 CDP's dedicated headphone amp whose use doesn't mute the output when the 'phones are plugged in. That got me in trouble a couple of times with the old amp and my CFO early on a Sunday AM when she was trying to sleep late... hard to explain while Clapton was coming from the Heresys and there I sat at my desk with 'phones on!

As an amp, it's $229 price isn't bad - mine was $195 on a Seasonal sale. It's a great 'headphone amp', too - I'm listening to the Ramsey Lewis Trio - oldies but goodies on the Pro-4AA's now. The drivers are from my original 71 set - re-homed in a new headset when I returned them in a body bag last year - along with $9 for s&h. Great warranty - and they do sound different from the current set I bought a few years back - better - more mellow. Then there is the nostalgia value...

 

[L1C4]

Headphones are not my area of expertise, so I have a question: how many headphones really need separate amplifiers? I have never had the problem of an amplifier not getting the headphones loud enough for my tastes, from any generic headphone jack I have ever used. I can maybe see a headphone with a very erratic impedance profile benefiting from robust amplification, if that impedance profile can actually affect frequency response from so-so amplifiers, but that would seem to be more of an issue of a problematic headphone rather than necessitating a separate headphone amplifier. I can see getting a DAC for headphones since some of the generic jacks I have used have had electric noise leak into the signal.

Are there so many high-resistance and low-sensitivity headphones out there that typical jacks do not offer enough amplification and separate headphone amps are a big thing? Something else I have noticed in recent years is AVRs, integrated amplifiers, USB sound interfaces for computers, USB DACs for PCs, is that they are starting to hype high-quality built-in headphone jacks as a feature, so this would seem to lessen the need for separate headphone amplifiers even more so.

Just for an example, I have to run my AKG K1000s ear speakers (headphones) off of two 300b monoblocks that output 2W each, one for each channel. I connect it using a speaker tap adapter cable. The lower efficiency headphones are the hardest to drive (e.g. AKG K1000, HE-6) which typically requires more power than your average balanced or unbalanced headphone output can provide.

 

[shadyJ]

Just for an example, I have to run my AKG K1000s ear speakers (headphones) off of two 300b monoblocks that output 2W each, one for each channel. I connect it using a speaker tap adapter cable. The lower efficiency headphones are the hardest to drive (e.g. AKG K1000, HE-6) which typically requires more power than your average balanced or unbalanced headphone output can provide.

Is there some kind of performance benefit that merits that kind of efficiency trade-off? In speakers, sensitivity is traded for bass extension or physical size. What do you get for lower efficiency in headphones?

 

[L1C4]

Is there some kind of performance benefit that merits that kind of efficiency trade-off? In speakers, sensitivity is traded for bass extension or physical size. What do you get for lower efficiency in headphones?

The one odd thing about headphones versus speakers is that a lot of it is opposite. For example, the higher efficiency headphones that tend to be easier to power run 150+ ohms.

The bonus that you get is an extremely wide and accurate soundstage. You get full extension in both the highs and lows, while still delivering incredibly dynamic SQ. However, it's very expensive to get the right setup and the headphones that fall into that category also tend to be expensive.

 

[shadyJ]

The bonus that you get is an extremely wide and accurate soundstage. You get full extension in both the highs and lows, while still delivering incredibly dynamic SQ. However, it's very expensive to get the right setup and the headphones that fall into that category also tend to be expensive.

It's not clear to me what is it about the high impedance that the headphone driver can use to create a better sound. I will have to look into how headphone drivers work.

 

[L1C4]

It's not clear to me what is it about the high impedance that the headphone driver can use to create a better sound. I will have to look into how headphone drivers work.

Do you mean in that scenario? The headphones I'm speaking of that are low efficiency tend to have a low SPL and relatively low Impedance as well. Typically, <75.

 

[shadyJ]

Is the low efficiency due to a heavier moving mass, ie a large diaphram or heavy coil?

 

[L1C4]

Is the low efficiency due to a heavier moving mass, ie a large diaphram or heavy coil?

Predominantly, yes.

 

[Boerd]

For most headphones the only benefit of a headamp is a happy audio dealer. Your iPhone is as clean as it can be. There are websites with detailed measurements of what an iPhone can do. I have some of the least sensitive headphones - the Beyer 880 at 600 ohms. The ipHone can drive them loud. The iPhone puts out around 1 Vrms and the 880 needs 0.54Vrms for 90db so it will drive the 880 to around 96-97db at max volume. That is loud for somebody with intact hearing.
What I noticed is that a lot of "audiophiles" listen to very loud music because they have hearing damage. Yes - it begs the question if they can be called "audiophiles" anymore, but that's another question.
I bought my Chord Mojo simply as a toy; same with the LCD-4. The 4k$ spent on the LCD-4 is for an incremental improvement over a HD 650 or Beyer 880 / 600. The one thing I like the LCD-4 for is the clean low-frequency reproduction.
Anyway - for most headphones a person with decent hearing doesn't need more than an iPhone. The iPhone at max volume still has enough headroom that is does not clip (good engineering).
http://www.kenrockwell.com/apple/iphone-6-plus.htm#measurements

 

[JRT3]

I'll restate the obvious. If you 'need' a dedicated headphone amp, the Emotiva 50 Wpc A-100 BAS-X is a bargain @ $229. If your lo-Z 'phones need more power, you could always parallel the 250 Ohm 5W current limiting resistors, or, if you are really careful, you could employ the included shorting jumpers! As a side note, you could also connect a pair of efficient bookshelf speakers to the amp when you tire of being tethered to your amp (My older Heresys are a good match to this amp in my office.).

After 4+ months, the only negative I have found with the little Emo amp is the volume control knob. Unlike the previous model, which didn't include a headphone jack, there isn't a hole bored thru the new amp's knob which would permit the blue ring of light at the knob's skirt to propagate thru and give you a blue reference dot so you could tell the control's setting from a distance. The knob is devoid of markings as delivered. The folks at Emo were shocked when I brought this to their attention - and, no, they din't have any spare earlier amp knobs! Not a deal killer, of course.

John

 

[Good4it]

I have HD800 and Audese LH-8s and my iPad drives them both very well.