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Old 14th July 2012, 01:48 PM   #1
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Richard Murdey
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Default What is a portable headphone amplifier?

I suspect you may know already where I'm going with this, but, let me ask it in general terms:

1. How small does it have to be?
2. How heavy?
3. How long does the batteries have to last?
4. Does it need gain?
5. How about a volume control?

I ask sincerely because personally I do not listen to music outside of my home. It wouldn't occur to me to try. I am quite happy with so-called "desktop" headphone amplifiers powered from AC, and large, over-ear headphones. However, as a design exercise, I am amusing myself with the notion of putting together a battery powered "portable" headphone amp.

One last question, it's a little loaded, but still -

"Given that your portable device you use as a source (iPhone, PMP, "digital transport") is battery powered and uses an op amp output stage for the headphone output, what listed "feature", if anything, would convince you that a separate headphone amplifier, also battery-operated and op amp-based, would significantly improve the sound?"

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Last edited by rjm; 14th July 2012 at 01:51 PM.
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Old 14th July 2012, 02:06 PM   #2
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you could check out the existing suppliers, kit projects for ad copy justifications

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Old 14th July 2012, 02:58 PM   #3
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Quote:
Originally Posted by rjm View Post
1. How small does it have to be?
2. How heavy?
3. How long does the batteries have to last?
4. Does it need gain?
5. How about a volume control?
Every single one of those is up to the user to decide. It's not "one size fits all".


Quote:
Originally Posted by rjm View Post
Given that your portable device you use as a source (iPhone, PMP, "digital transport") is battery powered and uses an op amp output stage for the headphone output, what listed "feature", if anything, would convince you that a separate headphone amplifier, also battery-operated and op amp-based, would significantly improve the sound?"
There are multiple reasons why the device amplifier could be inadequate....

Not enough gain (i.e. driving high impedance loads).
Not enough current drive (weak/sloppy/distored bass).
Device amplifier produces less distorion into high impedance (i.e. external amp inputs).
High noise floor with digital volume (external analog volume control can help mask this).
And last but not least, people just like to build things.... so what if they have no real need for it.

I'm sure there's more.
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Old 14th July 2012, 03:39 PM   #4
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The most ridiculous product I ever saw was a Remote Control Personal Headphone Amplifier. The amp itself was strapped to the user as an accessory, who would be SO LAZY as to not change the volume by reaching to their body ?????
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Old 17th July 2012, 01:15 AM   #5
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Quote:
Originally Posted by theAnonymous1 View Post
Every single one of those is up to the user to decide. It's not "one size fits all".
I understand that, I'm interested in the statistics. Mean and distribution width. I want to know if what most people will accept as portable is feasible for through-hole, DIY level component densities, for anything with parts count higher than a Chu-Moy...



Quote:
Originally Posted by theAnonymous1 View Post
There are multiple reasons why the device amplifier could be inadequate....

Not enough gain (i.e. driving high impedance loads).
Not enough current drive (weak/sloppy/distored bass).
Device amplifier produces less distorion into high impedance (i.e. external amp inputs).
High noise floor with digital volume (external analog volume control can help mask this).
And last but not least, people just like to build things.... so what if they have no real need for it.
Very good list. Of which I think the first and last are the only two that really matter. A dedicated headphone out of the device should handle output current, low impedance loads just as well as an generic op amp (or two), and digital volume controls are pretty transparent nowadays.
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Old 18th July 2012, 07:34 AM   #6
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Quote:
Originally Posted by KatieandDad View Post
The most ridiculous product I ever saw was a Remote Control Personal Headphone Amplifier. The amp itself was strapped to the user as an accessory, who would be SO LAZY as to not change the volume by reaching to their body ?????
I am not aware of the product that you are referring to.

During the Walkman/Discman era, the higher end portable player comes with earphone cable inline remotes, so one can skip songs or adjust volume while keeping the player in a bagpack. I suppose the product that you are talking about is meant for similar purpose? But if the remote is IR which requires line of sight it would indeed be silly.

Or is it meant to be used with a non portable source and a long headphone cable? Often I do wish that my non portable headphone amps have remotes.
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Old 18th July 2012, 07:42 AM   #7
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To OP,

I think there is another important questions to ask. That is what kind of headphone is it meant for? This would have significant impact to the answer to your questions, and the answer would be personal preference.

As for your last loaded questions , personally, it would be improvement in sound quality alone that matters, but people here tend to be more immune to marketing mambo jambo. This aspect IMO is really hard to achieve given the limitation in size, power, source and headphone used with it.
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Old 18th July 2012, 11:14 AM   #8
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Basically, if it fits in my hand it's portable.
Weight << a brick.
Volume control isn't absolutely necessary, unless we're talking mass-market item. Then it's standard feature.
If it's transparent and without gain, what exactly is it expected to do?
For the last question, I can only say that one listen through a headphone amp versus "the standard output" was all the convincing I needed. The first I owned had a 5-band EQ and was used with walkmans and as a preamp for battery-powered active speakers. I have probably half a dozen now.
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Old 19th July 2012, 01:36 AM   #9
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Re. the what kind of headphones is it meant for? question.

Yes, at the end of the day this is the alpha and omega of headphone amp design, since headphones comes is such a wide range of load impedance and sensitivities. To be all-inclusive, a headphone amp not only has to be overbuilt to handle extremes of both current and voltage, but also has to work at a range of gains. Both are at odds with a compact, simple, efficient portable amplifier.

Ok, in real life it isn't all that hard, but the fact does remain you can free up design resources if you decide to optimize the headphone amp for high current or high voltage rather than both.
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Old 20th July 2012, 12:38 AM   #10
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Since I don't take high impedance phones outdoors my portable headphones are usually the low impedance high sensitivity stuff, so I guess no voltage gain, for IEMs maybe even a step-down transformer.

Really whatever drives 16 Ohm headphones with relatively low distortion while preserving good SNR and keeping size/weight to a minimum. If on batteries I'd expect it to last a good 12 hours or more.
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