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Quality Headphone Amplification

Sal1950

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With the recent hit of ultra expensive ($3-5k+) headphone amps from Pass Labs, McIntosh, etc; and the hundreds of models from a $100 to $1k I've been wondering what it takes to make a great headphone amp circuit? Ignoring the excesses of the luxury goods clan, and the fact that many also sub as DACs and Preamps,
just what is required for the headphones themselves. Since the earliest days of HiFi a internal tap and output jack has been standard equipment on most everything that produced sound.
Hoping to get some input from the techs here on what is important in the amp design..........
 

RayDunzl

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Sal1950

Sal1950

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Interesting further happenings.
The of the components that actually inspired this post was the newish Audeze-The King ($3,995) that was "impression-ed" by Herb Reichert in the December Stereophile. Glowing words were written of course but hard to decipher since he actually wrote a few mini reviews of The King when paired with half a dozen different headphones................
So today the mailman delivered the January issue in which John Atkinson did a full series of in-depth measurements. If you read the article he had actually did the measurements before he handed off the King to Reichert so these these results existed before Herbs glowing article last month but were held back till now?
In any case John found some very disappointing S/N ratio numbers (53.9L/61.3R) and a few other hiccups you wouldn't expect from a $4k SOTA product. Problems the others here would understand much better than I. Of course John then slights the bad measurements with remarks that they probably don't effect The King in any audible way but that he was very "bothered by the character of the noise floor"? :rolleyes:
So then I jump ahead to back of the magazine and the Manufacturers Comments from Audeze.
According to the CEO that particular amp was made this April. (original product looks to have been released in late summer 2015) Shortly after April the senior engineers met with designer Bascom King to discuss improving the S/N and increasing the amps power. They first decided on a change in grounding scheme that immediately improved SNR and that change was implemented right away. Then sometime in the future there will be a "more powerful version" which should even further improve measured performance?

To me another interesting look inside "Luxury" High End audio and marketing.
Here we have what you would expect to be SOTA but instead was released to the public with less than stellar performance.
It was also released for review by Stereophile, got a glowing listening review, while all along John and whoever else there, already knew there were issues with measured performance of the reviewed unit. Info that was held back till the manufacturer had a chance to put together a response? Info that was held back till the original glowing review could have it's impact and the negative measurement follow-up was then published the next month on page 133. :D

I may be paranoid but that doesn't mean no one is following me. ;)
 

amirm

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It sure looks like they don't what they are doing and/or had no measurement gear. No way is 53 to 60 db S/N is adequate. That is cassette tape territory noise figures and we all know that was not a quiet medium.
 

RayDunzl

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My HD650 specs:

Nominal impedance 300 
Sound pressure level at 1 kHz 103 dB (1 Vrms)
Long-term input power max. 500 mW as per EN 60-268-7
THD ≤ 0.05% (1 kHz, 100 dB)

So, that's 103dB sound level with 0.003 Watts.

sometime in the future there will be a "more powerful version"

Hmm...

500mW long term power... That would be: 12.24V and 124.75dB (maybe).
 
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Sal1950

Sal1950

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Hmm...
500mW long term power... That would be: 12.24V and 124.75dB (maybe).
Yes, our HD-650's are a bit power hungry but how much is really needed?
I do on occasion plug them directly into my tower PC for a quick listen when I don't feel firing up the Emo DC-1 just for a this or that. Onboard sound can drive the cans easily to any level I've needed at the time but the Emo does sound decidedly better in all areas. This info was posted in the DC-1 thread over at headfi by the guys from Emotiva.

Keith Levkoff replied:

These were run manually on the AP, so you don't get a pretty formatted report.... (I'll be posting them later tonight)

DC-1 Headphone amp:

NOTE: The two headphone outputs are entirely independent - each has its own amplifier/driver
(you can't set them to different levels, but these specs are for EACH one)
These are with the frequency response jumper set to FLAT

Frequency Response: 20 Hz - 20 kHz +/- 0.14 dB (at 1 V output)
THD: < 0.025% (at 1 V output; at 1 kHz)
S/N: > 101 dB (ref 1 V output; A weighted)

Power output:
750 mW into 8 ohms
1200 mW into 32 ohms
180 mW into 300 ohms
90 mW into 620 ohms
Keith Levkoff
Technical Writer

-----------------------------------------------------------
I never did understand what Nick meant by,
"The low impedance circuit can run down to virtually 0 ohms" ?

Nick Hetzler replied:

Hello,
Thank you for your interest in Emotiva Pro. I will get the headphone amp specs for you as soon as possible. The low impedance circuit can run down to virtually 0 ohms but I will have to check the power output for you. Thank you, I will get back with you on this info.

Best Regards,
Nick Hetzler
Product Specialist
 

Phelonious Ponk

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I've often wondered if the "need" for amplification to properly drive high-impedance headphones is another audiophile myth. Has any one ever seen a comparison of the measured performance of some well-known "difficult" headphone loads with and without dedicated amplification?

Tim
 

amirm

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Tim, I tested amplifiers many years ago and I was shocked at how much louder, dynamic and improved bass they bring. This was over laptop and portable audio players.

The default output amp in these devices is designed for cost and power efficiency so don't have the oomph to drive these deaf ears properly. :)
 

Phelonious Ponk

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Tim, I tested amplifiers many years ago and I was shocked at how much louder, dynamic and improved bass they bring. This was over laptop and portable audio players.

The default output amp in these devices is designed for cost and power efficiency so don't have the oomph to drive these deaf ears properly. :)

Thanks, Amir. I've run my trusty old Senns through amps and directly off of the output of portable devices and thought I heard a significant difference, but I've thought I heard things that weren't there before.

Tim
 
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Sal1950

Sal1950

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Tim, I tested amplifiers many years ago and I was shocked at how much louder, dynamic and improved bass they bring. This was over laptop and portable audio players.

The default output amp in these devices is designed for cost and power efficiency so don't have the oomph to drive these deaf ears properly. :)
My hope in starting this thread was that in the face of multi-thousand dollar headphone amps, to get some detail into what might really be required to create a good amp. Something transparent yet providing enough power to handle the difficult loads. To a layman such as myself it seems a simple task, a good power supply and a couple chips or tubes and wah-la, you should have nirvana. ;) Indeed the market is swarming with units in the $100-200 range that "should" fit the bill?
But then we have the High End Audio market where,
Tiny thumb sized USB doogles like the AQ DragonFlys. Running on the clients unknown quality power supply, they cram the amp and DAC into a itty bitty thumbdrive. Then this product goes on to receive SQ kudos from everyone who receives AQ advertising dollars, including two "Product of the Year" awards from Stereophile. :eek:
At the other extreme are the $4k+ amps from Audeze, Pass, McIntosh, etc; that to me seem like monsterish overkill, though admittedly many are multi-functional devices. Mc's latest MHA 150 billed as a "headphone amp" is actually a DAC, PreAmp, Headphone Amp, and 50 wpc power amp all rolled into one. I'd call that a integrated amp plus DAC. LOL
There are just so many stinky fish swimming in the headphone amp stories of our High Fidelity world.:( I was looking to separate the BS from the reality here.
Amir or anyone, without going into extreme detail, what pieces would you be looking to gather if you wanted to build your own headphone amp? ;)
 

tomelex

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It depends on what you are looking for. For example, if you want the SET "coloration" then you need SET amp to get it. If you want an ultra replication of the original signal, you want low impedance, ultra low distortion that is measured at say 1mw and noise measured there too. This is about ultra low power amps, as mentioned before, and for headphones, noise and super low distortion at really low power are the two biggies in my book for solid state amplification. Noise specs at full power are absolutely worthless and deceiving when it comes to headphone amps. Class A "by a competent designer" will give you lowest distortion but good luck finding noise specs at say 1 milliwatt from most of the players. The reason you sort of want a mini power amp is the speakers have varying impedance but also the cables have capacitance that you need to drive as well.
 

RayDunzl

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Amir or anyone, without going into extreme detail, what pieces would you be looking to gather if you wanted to build your own headphone amp?

Assuming a certain amount of "power" is needed in the analog musical signal to get the headphone drivers to do their thing, creating a varying electromagnetic field to react with a static magnetic field, pushing and pulling on a diaphragm submerged in viscous air...

Ohms-Law-Formula-Wheel.png


All other things being equal:

A low impedance headphone will operate with a lower signal voltage, but suck more current (it's not a lot of current - micro to milliamps). Good for battery operated devices where there might not be much voltage available.

A high impedance phone will suck less current, but need a higher voltage signal to deliver the same power to the drivers. Think something that plugs in the wall with a transformer (or other modern convenience) in its power supply to bump the voltages above simple battery levels.

---

From somebody looking at my DAC's headphone jacks:

"The headphone outputs are driven by a pair of TI LME49600 high-current audio buffers. Judging by the specifications and the simplified schematic diagram in the datasheet, this chip is similar to the Texas Instruments/Burr-Brown BUF634. It’s an open-loop, current-feedback device with a slew rate of 2,000 V/µSec, output current of 250 mA, bandwidth adjustable from 110 to 180 MHz, and is designed to be used with an op-amp inside the feedback loop. The LME49600 has been designed especially for high-performance audio applications with a THD of 0.00003%, and maximum DC supply voltages of ±20 V (the older BUF634 is limited to ±18 V rails and the THD is not specified for that device). The high output current of the LME49600 buffers enables headphones to be directly driven—no series output resistor is used, yielding a 0-ohm output impedance. Most headphone amplifiers have some resistance in series with the outputs, which is usually at least 10 Ω and often higher with circuits based on unbuffered op-amps. Since headphones don’t have flat impedances curves, the series output resistor alters the frequency response and degrades the damping factor. Benchmark’s design is the best possible solution for headphone amplification."

From TI:

http://www.ti.com/product/LME49600

Looks like the power supply can be up to 18 Volts.

---

Also from TI - list of headphone driver chips:

http://www.ti.com/lsds/ti/audio-ic/headphone-amplifier-product.page

You get choices.

Power supply required as low as 1.6 Volts.

---

Or you can draw up a circuit and build a little amplifier from discrete parts to your own liking.

Example:

headphone-amp-schematic.GIF
 
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Sal1950

Sal1950

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Thanks for the detailed input guys. Putting together info like this sheds light on what it may take to design a great amp and lets consumers have some greater insight into the things that are really important in their HiFi purchases.
The headphone outputs are driven by a pair of TI LME49600 high-current audio buffers. Judging by the specifications and the simplified schematic diagram in the datasheet, this chip is similar to the Texas Instruments/Burr-Brown BUF634.
Interesting as that's the chip Emotiva chose to use in the DC-1. They use a pair of them to drive each of the dual headphone outs independently. Good choice for his/her users that may want to listen together. ;)
Or you can draw up a circuit and build a little amplifier from discrete parts to your own liking.
Sounds like fun but maybe a bit beyond my skills when it came to picking the correct parts. But there are a crap load of both tube and SS kits available.
In any case DIY is beyond the scope of where I wanted to go with this thread.
Cheers
 

Blumlein 88

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https://emotiva.com/products/amplifiers/100

Should be a superb headphone amp as it offers direct tapping of the power outputs for headphone use. I have an old Sherwood MOSFET receiver setup this way and it will play headphones till the cows come home. It would drive all but the very gnarliest headphone loads with ease. All for $195.
 
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Sal1950

Sal1950

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https://emotiva.com/products/amplifiers/100

Should be a superb headphone amp as it offers direct tapping of the power outputs for headphone use. I have an old Sherwood MOSFET receiver setup this way and it will play headphones till the cows come home. It would drive all but the very gnarliest headphone loads with ease. All for $195.
Emotiva offers some very interestingly designed components. Amir's possible worries in another thread of the parts quality may be justified, I don't know. But the almost throw away pricing makes concerns for a 25+ year life basically irrelevant.
 

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I have headphone amps ranging from a $99 single-ended job with a built-in DAC and to massively over-powered fully-balanced discrete solid-state tube hybrid for about $800.

My more modern cans, the ones designed since the rise of smart phones, perform equally well on either -- they're higher sensitivity, have benign impedance curves, and clearly designed with "mobile first" in mind.

But some of my more classic models, with designs dating back a few decades, clearly sound better with the higher powered amp; this isn't too surprising, as often they're lower efficiency. Also my planar headphones definitely do better on the bigger amp.

It's just like speaker -- you need to match the requirements of your transducers to the amplification.
 

watchnerd

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Amir or anyone, without going into extreme detail, what pieces would you be looking to gather if you wanted to build your own headphone amp? ;)

Tell me what headphone you're trying to drive -- without knowing that, the answers will be vague.
 

amirm

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A headphone amp discussion cannot be without a mention of CMOY DIY types. These are simple headphone amps put together with OpAmp ICs and just a handful of parts. Then folks get creative and put them in Altoid boxes. Here is one of countless examples: https://www.amazon.com/Audiophile-headphone-amplifier-parts-Altoids-Wintergreen/dp/B00H7JAPD4

61aR1AnSVaL._SL1200_.jpg


There is a whole cult following with folks trying everything under the sun to make these: https://en.wikipedia.org/wiki/CMoy

It is a fun introduction to electronics to build one. I helped my son make one and the improvement over stock portable audio player was quite significant.
 

watchnerd

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A headphone amp discussion cannot be without a mention of CMOY DIY types. These are simple headphone amps put together with OpAmp ICs and just a handful of parts. Then folks get creative and put them in Altoid boxes. Here is one of countless examples: https://www.amazon.com/Audiophile-headphone-amplifier-parts-Altoids-Wintergreen/dp/B00H7JAPD4

61aR1AnSVaL._SL1200_.jpg


There is a whole cult following with folks trying everything under the sun to make these: https://en.wikipedia.org/wiki/CMoy

It is a fun introduction to electronics to build one. I helped my son make one and the improvement over stock portable audio player was quite significant.

It's even better with Blu Tack inside.
 
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