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Engineering

As I'm an electronic engineer, I'm curious about the way equipment is built. This page gives some inside information about the iPod.

To see how to open an iPod, look at the iPod Batteries website. iPodLinux gives a nice overview of the chipset used in the different iPod models. Some sites show a tear-down of the iPod, like:
- Anandtech (3G).
- Jeffereies (5G).
- Artstechnica (5G).
- Portelligent (3G).

Electronics Design Chain Magazine has an article giving backgrounds about the iPod design. Portalplayer creates the central heart of the iPod (user interface, glue-ing the interfaces, decoding the audio). The following figure shows the components inside the PortalPlayer PP5002 chip:



Though not explicitly shown, from Portalplayer's website it is clear that the chip contains an SPDIF output. This option has unfortunately not been utilized by Apple, so it is not available on the standard connector.

Because of the increase in mobile devices, there are many questions about batteries. A good introduction about good battery usage can be found at the Battery University and the iPod Battery FAQ. The hard disk is from Toshiba. The iPod operating system is provided by Quadros Systems. Some hackers even manage to get Linux running on the iPod. Fun, but what's the purpose? The iPod database format can be found at Simon's page.

As mentioned on the comparison page, different generations of iPod have a different sound characteristics. Especially the 3G and 4G have a lack of bass, caused by a low output capacitor in the output section of the Wolfson headphones driver. The following figure (all roughly on the same scale) shows the dimensions of the capacitors of different iPod generations. I guess this explains a lot, especially for the 4G. The 5G uses another Wolfson chip, which is not documented on the web, so it is difficult to find out which capacitor values are required.

Measurements

Measurements can be used to give some specific characteristics of a device, but they don't define the sound quality of a device. A flat response from 20Hzへるつ to 20kHzきろへるつ says something about the static response (sweep measured) or average response (white noise measured) of a device. It doesn't tell you for instance about the characteristics of a power supply when it instantly needs to deliver a certain amount of charge because of a sound transient. Measurements also don't tell you if a device sounds "nice" or "nasty", e.g. a distorting tube amplifier can sound much nicer than a flat-response cheapo transistor amplifier. Measurements can be used to find flaws (if severe deviations from expected behavior is found), or to find some characteristics of a device (e.g. noise shaping).

Though I've performed some measurements on the iPod myself, the October 2003 issue of Stereophile has published an extensive review and measurement set of the iPod 3G. The measurements show that the iPod is free from major artifacts. The static performance of the digital circuitry is quite good (better than many CD players), and the line output is well defined as well. The bass response on the headphones output is seriously flawed due to too small output capacitances in the 3G. A Stereoplay measurement of the 3G confirms the lack of bass:


[StereoPlay, 2003]

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