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Dean 
Special Collaborator
Retired Admin and Amateur Layabout
Joined: May 13 2007
Location: Europe
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Points: 37575
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 Posted: February 18 2011 at 06:22 |
 Mr ProgFreak wrote:
I think that especially for portable use, the goal is to build headphones that are smaller, but without sacrificing sound quality. I think the proper way to go is in ear headphones (like the ones I showed above). Move the speaker as close to the eardrum as possible - then it can be an order of magnitude less loud (thus consuming much less power), and since it's lodged in the ear canal it naturally blocks surrounding noise.
Surely there are more expensive choices of in-ear headphones than the one I listed above - but because of the advantages I listed above, even in the 50 EUR price range there are some which sound amazing. The biggest disadvantage is that they tend to slip out of the ear, so you end up re-adjusting their fit frequently. And that's the big advantage of my bluetooth headset: It's designed to prevent exactly that. I've already tried cycling and jogging with it, and it works just fine. |
I agree - the real "gem" in Oliver's set-up is the headphone amp, and that power is needed to drive the cans without producing the excessive distortion the iPod would create into that load at those power levels. The iMod and the OFC cable is cosmetic in my opinion.
With more efficient ear buds the reduced drive power improves the distortion considerably (and reduces battery drain). To achieve what Oliver is attempting you really do need to spend a serious amount of money on the external Class-D amp - those cheaper (sub $100) ones aren't much better than the iPod itself - the FiiO E5 for example can only kick out 150mW into 16ohms and cannot drive big headphones.
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Dean
Special Collaborator
Retired Admin and Amateur Layabout
Joined: May 13 2007
Location: Europe
Status: Offline
Points: 37575
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Posted: February 18 2011 at 05:32 |
ps: there is a better way of modifying an iPod, and that is to do away with the DC blocking capacitors completely ("capless" in the graph below) - there is a third audio output associated with the L/ROUT1 connections that outputs the Voltage Reference level called MONOOUT - using this as a phantom ground connection for the headphones/line-out removes the DC component completely, which not only improves the THD, it also improves the bass frequency response since it does away with this low-cut filter of the capacitor/load. The disadvantage is that the ground connection of the output is no longer 0V, but since the iPod is floating that is not a problem.
The THD can be improved further still on some newer Wolfson codecs by increasing the supply voltage to the output amplifiers to 5V (SPKRVDD), but I don't think this is possible on the 4g and 5g iPods.
Edited by Dean - February 18 2011 at 05:52
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Dean
Special Collaborator
Retired Admin and Amateur Layabout
Joined: May 13 2007
Location: Europe
Status: Offline
Points: 37575
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Posted: February 18 2011 at 04:58 |
oliverstoned wrote:
I don't understand the last part of your sentence, sorry for my bad english:"but $250 to have someone bypass that amp is a little expensive."
..and i'm not rich, just broken by Hifi!
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The Wolfson codec has 2 pairs of outputs LOUT1 & ROUT1 and LOUT2 & ROUT2 - all of these are designed to be either Line Out or Headphone Out ... the L/ROUT2 outputs can also be configured to drive a mono speaker in bridge configuration (not used on iPods). All of these outputs have the same specification, however in the iPod the L/ROUT1 connections are used to connect to the headphone socket and will give 0.013% (-78dB) THD at 20mW into 32ohm headphones - the L/ROUT2 ouputs will also produce that same THD value if driving into 32ohms. When driving into 10Kohm loads (ie as Line Out) the THD decreases to 0.006% (-84dB), which is obviously better - but any unmodified iPod can do this from the headphone socket. The THD is not determined by the Codec, but by the load ... change the load and you change the THD.
The iMod modification disconnects the headphone socket from L/ROUT1 and connects it to L/ROUT2 - to do this it needs to block the DC part of the signal, and they do it using two $15 "audiophile" capacitors, bypassing the cheap surface mount ones used by Apple on the L/ROUT1 outputs. This I believe is an error, since the Apple software does not program the volume level on these outputs (it could, but does not) - a better mod for the same "cost" would have been to replace the Apple capacitors with the Black Gate Hi-Q ones, which would give the same spec but retain the volume control capability. However, this destroys the Emperor's New Clothes effect since the modified iPod would be exactly the same as an unmodified one.
The L/ROUT2 outputs are not inherently "quality" outputs - the specification of the L/ROUT2 driving into 10K is 0.006% - the same outputs driving into 8ohms is 1% THD ... all you are doing is changing the load, not the characteristics of the iPod outputs - even with the Black Gate Hi-Q capacitors those outputs will still drive headphones and they will give the same THD as an unmodified iPod driving the same headhones - Red Wine tell you not to connect headphones to the modified iPod because the volume is now set to maximum and cannot be controlled.
For the work they do $250 is not worth the money in my estimation.
Edited by Dean - February 18 2011 at 06:27
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Mr ProgFreak
Forum Senior Member
Joined: November 08 2008
Location: Sweden
Status: Offline
Points: 5195
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Posted: February 18 2011 at 03:36 |
I think that especially for portable use, the goal is to build headphones that are smaller, but without sacrificing sound quality. I think the proper way to go is in ear headphones (like the ones I showed above). Move the speaker as close to the eardrum as possible - then it can be an order of magnitude less loud (thus consuming much less power), and since it's lodged in the ear canal it naturally blocks surrounding noise.
Surely there are more expensive choices of in-ear headphones than the one I listed above - but because of the advantages I listed above, even in the 50 EUR price range there are some which sound amazing. The biggest disadvantage is that they tend to slip out of the ear, so you end up re-adjusting their fit frequently. And that's the big advantage of my bluetooth headset: It's designed to prevent exactly that. I've already tried cycling and jogging with it, and it works just fine.
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oliverstoned
Special Collaborator
Honorary Collaborator
Joined: March 26 2004
Location: France
Status: Offline
Points: 6308
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Posted: February 18 2011 at 01:49 |
Dean wrote:
With your money and my sense I could rule the world. 
The Wolfson DAC in the iPod is a pretty good codec that wouldn't disgrace a mid-range CD player and the headphone amp isn't up to the same standard by a long way, but $250 to have someone bypass that amp is a little expensive. |
I agree with the first statement: "The Wolfson DAC in the iPod is a pretty good codec that wouldn't disgrace a mid-range CD player"
The aim of a (good) portabLE amp is to provide enough power to drive correctly efficient cans (no way to drive properly a HD600 or equivalent with a portable amp, you need a real home amp for such cans)
but it really enhanced most good efficient cans. I talk about GOOD portable amps, indeed better nothing than a average amp.
I don't understand the last part of your sentence, sorry for my bad english:"but $250 to have someone bypass that amp is a little expensive."
..and i'm not rich, just broken by Hifi!
Edited by oliverstoned - February 18 2011 at 02:19
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Mr ProgFreak
Forum Senior Member
Joined: November 08 2008
Location: Sweden
Status: Offline
Points: 5195
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Posted: February 18 2011 at 01:37 |
iPad + Nokia BH-505 (Bluetooth headset). 
Sounds surprisingly good - but you have to use high bitrate or even lossless files because bluetooth will apply another round of lossy compression.
Edited by Mr ProgFreak - February 18 2011 at 01:39
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Dean
Special Collaborator
Retired Admin and Amateur Layabout
Joined: May 13 2007
Location: Europe
Status: Offline
Points: 37575
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Posted: February 17 2011 at 16:31 |
With your money and my sense I could rule the world.
The Wolfson DAC in the iPod is a pretty good codec that wouldn't disgrace a mid-range CD player and the headphone amp isn't up to the same standard by a long way, but $250 to have someone bypass that amp is a little expensive.
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oliverstoned
Special Collaborator
Honorary Collaborator
Joined: March 26 2004
Location: France
Status: Offline
Points: 6308
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Posted: February 17 2011 at 13:42 |
Any portaphile here?
Easier for me to enumerate my portable set up than my home setup...
Here it is:
Source: Imod (80 G Ipod modified by Red wine audio)+ ALO audio cable ("Jena labs" cable cryogenized with top notch plugs)
Portable amp: Qables Iqube (but i'd like to change for the much smaller RSA Mustang P51)
Headphones: Senn HD25 + Cardas cable
All the ingredients in picture for a killer 1500 dollars portable system (to use with wav files ripped from original new condition CDs) :
Edited by oliverstoned - February 17 2011 at 13:50
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Portaphile?
