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]

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!).

AAA batteries are huge.  You won't be able to fit even 1.

 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?

The charger probably would not work with NiMH.  They require different charging circuits.

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!).

If you do the research and can solder surface mount caps, then this could probably work.

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).

If you could fine a pin and software compatable replacement, you could do this.  Soldering it would be really difficult though.

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.

Where exactly are you going to put this amp?

[Sparky]

Hey,

Thanks for the response.

AAA batteries are huge.  You won't be able to fit even 1.

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.

Where exactly are you going to put this amp?

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]

AAA batteries are huge.  You won't be able to fit even 1.

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.

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]

AAA batteries are huge.  You won't be able to fit even 1.

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.

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.

[tychver]

Why not just build a battery box with a USB female socket in it? Four AAAs and you could have a 1AH external battery. Although if I'm going away I pack my  car charger, I did contemplate doing this. If you were really going to build something like this you would want the largest capacity batteries avaliable.

[Sentertainment]

Why not just build a battery box with a USB female socket in it? Four AAAs and you could have a 1AH external battery. Although if I'm going away I pack my  car charger, I did contemplate doing this. If you were really going to build something like this you would want the largest capacity batteries avaliable.

wouldn't 4@800mAH be more that that?

[soap]

Why not just build a battery box with a USB female socket in it? Four AAAs and you could have a 1AH external battery. Although if I'm going away I pack my  car charger, I did contemplate doing this. If you were really going to build something like this you would want the largest capacity batteries avaliable.

wouldn't 4@800mAH be more that that?

USB doesn't run off of 1.5 volts (AA/AAA).
Assuming 800mah AAAs:
Four AAA cells in series = 6 volts at 800mah.
Four AAA cells in parallel = 1.5 volts at 3200mah.

[reid]

If you do replace the wolfson codec (dac) how could one make it work. Could it be done now that an ipod has rockbox. Someone could come up with the proper settings for new dac? I also thought about possibly ( and tell me if this is stupid) getting an outboard adac to dac using the line out. Is that a really stupid idea or using the best of the best chips you dont have to worry about messing with the internal codec.

[saratoga]

If you do replace the wolfson codec (dac) how could one make it work. Could it be done now that an ipod has rockbox. Someone could come up with the proper settings for new dac?

Assuming you picked a DAC with a spec sheet, you could just write a dirver for it.  The hard part would be actually getting it onto the Ipod's board.  You'd probably never find one that was pin compatible.

I also thought about possibly ( and tell me if this is stupid) getting an outboard adac to dac using the line out. Is that a really stupid idea or using the best of the best chips you dont have to worry about messing with the internal codec.

The line out is analog, so you can't do that.  You'd need to use USB, and that would be extremely difficult since we don't have the USB stuff figured out (and no one is even quite sure if its possible though I suspect it is).

[reid]

Thats what i meant. use the analog line out and an analog to digital chip then digital to analog in an outboard setup. Using the best chips possible.

[saratoga]

Thats what i meant. use the analog line out and an analog to digital chip then digital to analog in an outboard setup. Using the best chips possible.

That makes no sense.  What exactly would the point be?

[reid]

Taking the analog signal and trying to properly convert it. So what could you use to make the signal better without touching the internals?

[soap]

Ignoring the faulty logic that A₁->D->A₂ can possibly be better than A₁....

What exactly is the problem with the analog signal coming out of the line-out port of the iPods?
For that matter - do you know what the problem with the analog signal coming out of the headphone jack is?  I'll offer you a hint - the problem - if it is a problem for you - isn't in the D-->A stage of the equation.

[saratoga]

Taking the analog signal and trying to properly convert it.

Think this through more carefully.  You're proposing to take an analog signal and "properly convert it" to analog.  This doesn't make logical sense, the signal is already analog, so the best you can possibly do is leave it alone.  Running it through another set of conversions compounds the noise in the signal with noise in the converters.

So what could you use to make the signal better without touching the internals?

At present, nothing.  Someday it might be possible to use an external DAC via USB, but I don't see that happening soon, and probably ever unless you're going to make it happen since it'd be an odd thing to do.