iPod Classic... DAC and output stage info from Vinnie of RWA - Page 9

Hi manaox2,

I need to get my hands on a 160GB drive and try it in my 5.5G iMod.

I read a pretty cool idea here (I forgot who posted this) that one can probably buy a 160GB iPod Classic for just a little more than buying the 160GB drive by itself. So just trade the 80 and 160GB drives between the 5.5G and the 6G. Then I guess you can sell the 80G 6G and that makes the price of the 160GB drive seem like a whole lot less!

Of course, I am only guessing that they will work. I still need to try it

I'll keep you all posted,

Vinnie

Hey guys,

For the 6G iPod Classic, all that is in the line-out signal path after the Apple CODEC is a tiny surface mount 10-ohm resistor, inductor (for HF noise filtering), and the the board traces that feed down to the dock connector.

I could bypass all of this and hard wire from the dac directly to the line-out using high-quality wire (like the Cardas wire that I use for the 5G/5.5G iMod), but I don't expect nearly the same kind of improvement as the iMod gives for the 4G, 5G/5.5G units. There is no opamp stage to bypass, no crappy coupling caps before and after the opamp stage to bypass, etc.

The "opamp output stage" (push-pull) is already built into the CODEC chip, and since it is running on a split (+/-) supply, there is no dc offset to filter with caps.

WindowsX,

Adding anything in the signal path such as a Vcap may alter the sound (based on the characteristics of the cap), but I believe we are really limited to the sound of this integrated dac + push-pull output stage chip.

The beauty of the 4G and 5G/5.5G iMod (line-out) is that the voltage output of the Wolfson dac was tapped directly and sent out (via a high quality cap), but no push-pull stage or opamp stage of any sort was in the path.

I can see the push-pull output stage as being a good thing for the headphone output (no bass rolloff issues, better drive with low-impedance headphones, etc.) but IMHO, this is not ideal for the line-out.

The only way to really improve the iPod Classic is to tap the native digital signals (I2S) that feed the internal dac and send them out to an external dac of higher quality. However, just about all external dacs use an SPDIF input, not I2S. I2S is something that you will find *inside* of an external dac, after the SPDIF has been passed through a receiver chip and converted over to I2S to feed the actual dac chip used in the external "dac unit."

As I mentioned eariler, the 6G iPod Classic is a very nice solution for those who are looking to connect directly to headphones, or even for those with a headphone amp. However, the more I listen to it and compare it to my 5.5G iMod + Vcap dock combo, the more I like the 5.5G iMod + Vcap dock combo

Best regards,

Vinnie