iPod with TDA2611A, Noise and other issues

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I am building a mono amplifier to work with my 1st generation iPod Nano that I want to give as a Christmas gift. The iPod's battery is dead and having no means of purchasing a similar one (or a phone battery), I've decided to power the iPod using an AC adapter (K30209 PSU link) that I found in a printer. It gives me two outputs: 24V@0.8A and 3.3V@0.15A which I found to be very convenient as I'll use the 24V output to power the TDA2611A (link to datasheet) power amplifier IC that I also found in my scrap box (It's actually the only IC that I have which can take up to 30V). Now, I managed to raise the 3.3V output to under 4V which is a little over the 3.7V rated battery the iPod originally had and it works. I also integrated a Stereo-To-Mono Summing circuit.

Please refer to the attachment as you read the following:

I followed the circuit on the IC data sheet, hooked it up to the headset output of the iPod and upon testing I ran into the first problem: The highs were too loud and harsh and it picked up a lot of interference when I turned on the iPod. As soon as the screen lit up, it sounded like a radio tuned between two stations. I found that by replacing the C2 (220pF recommended) with a higher value (over 100nF), it would cut down on the noise but it also acted like a Low-pass filter and I just couldn't dial in crisp highs and I was also losing volume. After some online reading, I've decided to use the Line Out of the iPod instead, which is said to have a higher impedance (I couldn't find any specs -- And impedance is something I don't understand) and that it will work better with an amplifier. I did just that and added a volume control and tested it. The sound appears to be cleaner, there's about half less noise, the mids and bass sound better but it's not good enough. With the iPod turned off and the amplifier powered, there's very little noise coming out of the speaker, barely noticeable. But once I turn on the iPod, even without playing a song, the sound is harsh and noisy. I couldn't find anything of help online so I've decided to ask here:

  1. Is it an impedance mismatch? Pins 5 and 9 on the IC allow increasing input impedance using a capacitor (1uF) and a resistor in series. I tried that with a 10k variable resistor and it didn't make any audible difference.
  2. The speaker I'm using (my only one) is rated at 7-7.5W and 4 Ohms whilst the IC recommends an 8 Ohm speaker. Are there any components that I need to change because of this?
  3. I've copied the Stereo-To-Mono summing circuit from another website but I have no idea if it works well with my setup.
  4. Could this be a ground loop issue?
  5. I wouldn't mind ditching this IC and doing a transistor amplifier if it would spare me of these issues but I don't know how to find a circuit that would work with an iPod. Specifically searching for an iPod transistor-based amplifier didn't return any useful results.

My second problem is the iPod crashing after playing 2-3 songs. It simply freezes and I have to turn off the power supply and then turn it back on. There's nothing getting hot in the iPod, the AC adapter still provides the (aprox.) 4 volts, and the amp IC is still working but the iPod stops responding. I'm hoping it's the software. Any ideas?


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