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?"
Hammond 1455 enclosures.
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?"
Hammond 1455 enclosures.
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you could check out the existing suppliers, kit projects for ad copy justifications
Portable Amps - Head-Fi.org Community
Portable Amps - Head-Fi.org Community
Every single one of those is up to the user to decide. It's not "one size fits all".
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.
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...
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
so we are defining a portable headphone amp as a generic opamp or 2? inbuilt headphone outs on daps are NOT capable of driving multidriver very low impedance monitors properly, they just arent. digital volume controls can be excellent these days, but they are generally not the type included in DAPs
Roughly speaking the basic quantities are:
Hope that helps.
- Size, probably no greater than 40 x 120 x 80mm
- Gain, with volume control 10dB, without 0dB
- With batteries (rechargeable of course), more than 3 hours operation
- A volume control is always a plus
Hope that helps
.
Gain? yes. More than 5V? Maybe not.
I have HD600s, same electrically as your HD580s. I know for a fact I never put more than 500 mV peak swing into the phones. (nominal SPL ~95-100 dB) Anything above that is just (way) too loud. So a well-designed headphone IC running on 5V Vcc would in principle be sufficient.
[q]
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'm just a newbie. But the Fiio E6 seems to fit the bill regarding.
1. Size looks good can be a bit bigger if need be. I guess you need to go SMD which makes it a bit more difficult for a DIY. But give people freedom to change opamps.
2. Weight looks good but can be a bit heavier I think. Like 50 grams. The E6 is only 16 grams which is really light.
3. 10 hours of battery time is good. Maybe a bit longer, but 10 will do the trick. Use a rechargeable Fiio like battery.
4. Yes. Without gain it's no amp right?
5. As far as I know it's 'cleaner' for your sound to control it from the amp then from the source.
5.1 EQ/bass button maybe. People tend to love bass related stuff I guess.
Hope this helps
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'm just a newbie. But the Fiio E6 seems to fit the bill regarding.
1. Size looks good can be a bit bigger if need be. I guess you need to go SMD which makes it a bit more difficult for a DIY. But give people freedom to change opamps.
2. Weight looks good but can be a bit heavier I think. Like 50 grams. The E6 is only 16 grams which is really light.
3. 10 hours of battery time is good. Maybe a bit longer, but 10 will do the trick. Use a rechargeable Fiio like battery.
4. Yes. Without gain it's no amp right?
5. As far as I know it's 'cleaner' for your sound to control it from the amp then from the source.
5.1 EQ/bass button maybe. People tend to love bass related stuff I guess
.Hope this helps
Watch carefully, I will only do this once:
Data encoded on CD 1 V peak.
Line level output of my DAC referenced to 1 V peak data is 2 Vrms or +6 dB.
Attenuation (highest volume control position I would ever use) -36 dB.
Gain of my headphone amp +22 dB.
Therefore the absolute max output voltage (CD clipping) is 6-36+22 = -8 dB.
That's 0.16 Vrms, or 0.09 mW into 300 ohms.
HD-600 sensitivity 97 dB/mW. So max SPL is 87 dB.
This is not actual output, this is the absolute max output possible from the signal chain at the chosen volume position. I do not, cannot, exceed 0.1 mW.
My estimate, that for ~100 dB/mW or higher headphones 0.5 mW is sufficient, stands. That's 500 mV peak voltage swings for 300 ohm phones, and something like 125 mV peak voltage for 16 ohm phones.
You can of course add all the headroom you want. This will allow the amp to work with low sensitivity headphones - something a little out of the design brief of a portable headphone amp. Normally it will never be used. It has the the downside of considerable extra power draw.
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