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iPod Modification Ideas
Sparky:
Hey,
I've just ordered an iPod, which should arrive in the next todays - for the sole reason that it will support Rockbox. Anyways, whilst waiting for Amazon's Super Saver delivery, I've got a few ideas which I might try when the iPod gets here:
1) Battery Upgrade: If I'm right, the battery in the iPod 5.5G is a 400 mAh Lithium Ion part. My idea here is to replace it with 3x 1000 mAh rechargable AAA batteries, which should take up about the same space as the stock batteries. If this works, then I might think about doing something to the iPod case to allow batteries to be swapped (imagine being able to just buy some new batteries if you are away from your charger!).
The only problems I see here are - 1) The batteries are NiMH type (will this cause any problems with charging? I'd also need to work out some kind of protection if non-rechargables are used), and 2) They are 1.2v each = 3.6v (iPod battery is 3.7) - will this cause any problems with Rockbox's measurements?
2) Output Stage (Headphone Driver) Capacitor Upgrade: I've heard that the iPod has a poor bass response with low impedance headphones (mine are 16 ohm). Apparently this is because the capacitors on the headphone driver are 220 uF. This creates a low-pass filter higher than the iPod's lowest frequency response (something around 25 Hz), if I remember the Wolfson document. That document also had a formula to work out the low-pass filter cutoff, so why not use 440 uF capacitors? These would create a sutiably low cutoff. If anyone has any suggestions here, it would be helpful (I don't want to mess up a new iPod!).
3) Replace the DAC: This crazy idea probably won't work, but if it can - why not replace the Wolfson DAC in the iPod with a higher-specced Wolfson model? I know there's no point - but still. I don't know too much about DACs - whether they can be programmed or if they just accept an input and give an output, but if it's possible you could even use a Burr Brown (TI) DAC, and get the best audio quality possible (FLAC files with an upgraded DAC and output stage would sound sublime).
4) Internal Headphone Amp: Even crazier idea! Instead of replacing the capactior on the headphone driver, it would great if it was possible to put a bespoke headphone amp (like the external ones you can buy...but internal) in the iPod. This could completely replace the existing output stage if possible, and a power supply that matches the battery life of the player would be needed inside. But if it can work - audio heaven! There would be no need for the line-out to connect to a headphone amp as this would completely replace the existing output stage.
I know these ideas are pretty crazy, but if anyone has any advice, I'd be willing to take my iPod furthur...
P.S. I'm completely new to Rockbox, and I'm an amateur coder, but if there's anyway I can help with the project, it would be fun and a great learning experience.
saratoga:
--- Quote from: Sparky on January 01, 2007, 02:40:16 PM ---
1) Battery Upgrade: If I'm right, the battery in the iPod 5.5G is a 400 mAh Lithium Ion part. My idea here is to replace it with 3x 1000 mAh rechargable AAA batteries, which should take up about the same space as the stock batteries. If this works, then I might think about doing something to the iPod case to allow batteries to be swapped (imagine being able to just buy some new batteries if you are away from your charger!).
--- End quote ---
AAA batteries are huge. You won't be able to fit even 1.
--- Quote from: Sparky on January 01, 2007, 02:40:16 PM --- The only problems I see here are - 1) The batteries are NiMH type (will this cause any problems with charging? I'd also need to work out some kind of protection if non-rechargables are used), and 2) They are 1.2v each = 3.6v (iPod battery is 3.7) - will this cause any problems with Rockbox's measurements?
--- End quote ---
The charger probably would not work with NiMH. They require different charging circuits.
--- Quote from: Sparky on January 01, 2007, 02:40:16 PM ---2) Output Stage (Headphone Driver) Capacitor Upgrade: I've heard that the iPod has a poor bass response with low impedance headphones (mine are 16 ohm). Apparently this is because the capacitors on the headphone driver are 220 uF. This creates a low-pass filter higher than the iPod's lowest frequency response (something around 25 Hz), if I remember the Wolfson document. That document also had a formula to work out the low-pass filter cutoff, so why not use 440 uF capacitors? These would create a sutiably low cutoff. If anyone has any suggestions here, it would be helpful (I don't want to mess up a new iPod!).
--- End quote ---
If you do the research and can solder surface mount caps, then this could probably work.
--- Quote from: Sparky on January 01, 2007, 02:40:16 PM ---3) Replace the DAC: This crazy idea probably won't work, but if it can - why not replace the Wolfson DAC in the iPod with a higher-specced Wolfson model? I know there's no point - but still. I don't know too much about DACs - whether they can be programmed or if they just accept an input and give an output, but if it's possible you could even use a Burr Brown (TI) DAC, and get the best audio quality possible (FLAC files with an upgraded DAC and output stage would sound sublime).
--- End quote ---
If you could fine a pin and software compatable replacement, you could do this. Soldering it would be really difficult though.
--- Quote from: Sparky on January 01, 2007, 02:40:16 PM ---4) Internal Headphone Amp: Even crazier idea! Instead of replacing the capactior on the headphone driver, it would great if it was possible to put a bespoke headphone amp (like the external ones you can buy...but internal) in the iPod. This could completely replace the existing output stage if possible, and a power supply that matches the battery life of the player would be needed inside. But if it can work - audio heaven! There would be no need for the line-out to connect to a headphone amp as this would completely replace the existing output stage.
--- End quote ---
Where exactly are you going to put this amp?
Sparky:
Hey,
Thanks for the response.
--- Quote ---AAA batteries are huge. You won't be able to fit even 1.
--- End quote ---
Are you sure? I'm getting the iPod today (hopefully), so I'll get the case off and have a look. I'm sure there's enough room for 3, but I could be wrong.
--- Quote ---Where exactly are you going to put this amp?
--- End quote ---
Again, I'll look at the iPod tonight, and I'll try to work out some plans. I suppose I could just upgrade the headphone amp - TI have some nice ones, but if I can fit a fully-fledged op-amp inside the iPod I'll try.
AlexP:
--- Quote from: Sparky on January 03, 2007, 02:53:10 AM ---
--- Quote ---AAA batteries are huge. You won't be able to fit even 1.
--- End quote ---
Are you sure? I'm getting the iPod today (hopefully), so I'll get the case off and have a look. I'm sure there's enough room for 3, but I could be wrong.
--- End quote ---
You are wrong. The standard battery apart from anything else is rectangular and very thin. The AAA's would probably (maybe) fit the footprint, but are many times thicker.
saratoga:
--- Quote from: Sparky on January 03, 2007, 02:53:10 AM ---
--- Quote ---AAA batteries are huge. You won't be able to fit even 1.
--- End quote ---
Are you sure? I'm getting the iPod today (hopefully), so I'll get the case off and have a look. I'm sure there's enough room for 3, but I could be wrong.
--- End quote ---
The thickness of the entire ipod video is the same as a single AAA battery. Even if the shell had no thickness, and the ipod had nothing inside, you could just barely fit it. In reality, there are things inside the ipod, which means you will not be able to fit a AAA.
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