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Old 25th July 2012, 07:53 AM   #11
dia is offline dia  Spain
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It is very light, easy to control, easy to carry,You can go look at Tinydeal
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Old 25th July 2012, 08:14 AM   #12
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Quote:
Originally Posted by rjm View Post
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.
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
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Old 25th July 2012, 12:20 PM   #13
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We are definitely not defining this as based on a generic op amp, only noting in passing that most portable headphone amps are designed as such - mainly as they easily and cheaply provide reasonable battery life + decent output power and distortion specifications...
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Old 30th July 2012, 04:58 PM   #14
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I would like a headphone amp because my Sennheiser HD580s are 300 ohms impedance and they require more voltage swing than an iPod etc. can provide. I need gain and higher voltage than a 5V supply.
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Old 30th July 2012, 06:23 PM   #15
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Roughly speaking the basic quantities are:

  • 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
In answer to your question, driving capability for less efficient headphones, ability to drive multiple headphones, output impedance (and possibly distortion).


Hope that helps .
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Old 30th July 2012, 10:41 PM   #16
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Quote:
Originally Posted by paulb View Post
I need gain and higher voltage than a 5V supply.
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.
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Old 2nd August 2012, 12:36 AM   #17
paulb is offline paulb  Canada
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Originally Posted by rjm View Post
...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.
The peak to average ratio in music is very large. If you're looking at 500mVp-p on a scope, chances are good that the music peaks out at maybe 10 times that value. I'd prefer to have lots of headroom, 20 - 40 dB above the average.
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Old 2nd August 2012, 02:33 AM   #18
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[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 :P.

Hope this helps
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Old 2nd August 2012, 04:05 AM   #19
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Quote:
Originally Posted by paulb View Post
The peak to average ratio in music is very large. If you're looking at 500mVp-p on a scope, chances are good that the music peaks out at maybe 10 times that value. I'd prefer to have lots of headroom, 20 - 40 dB above the average.
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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Last edited by rjm; 2nd August 2012 at 04:09 AM.
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Old 3rd August 2012, 03:26 PM   #20
paulb is offline paulb  Canada
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Quote:
Originally Posted by rjm View Post
Watch carefully, I will only do this once:
Good thing, because your flurry of calculations are irrelevant. To calculate peak voltage required all you need are the headphone sensitivity, impedance, and maximum SPL required.
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