[Vinnie R.]

All,

I spent a while checking out the motherboard of my new 60GB iPod Color.

Here is what I've found:

-- After the Wolfson 8975 dac, BOTH the line out and headphone outputs are sent into their own Analog Devices stereo opamps. My 20GB iPod (black and white), that I performed the iMod on, uses the same Wolfson 8975 dac, does not use the Analog Devices opamps. I knew they sounded a little different connected to my home stereo!

I suspect that the 60GB iPod Color will do a better job driving lower impedance headphones (due to the additonal drive that the opamp will provide), but I haven't tried it. The coupling caps used in the signal path of the headphone output circuit do not have their values written on them, so I'm not sure if they are larger enough to avoid the bass rolloff problem that many of you have experienced. Has anyone experieced bass rolloff with the 60GB iPod Color? I already found these caps to be too small in the 20GB iPod, which will definitely results in bass rolloff with headphones of 32-ohms or lower impedance.

-- From the pics of the insides of the iPod Nano, it looks like the Analog Devices opamps are not used and the circuit is just like my 20GB iPod.
The dac is a Wolfson 8975G (not sure what the "G" stands for), but they appear to have the same pin out for the line out and headphone outputs.
Again, I'm not sure if the coupling caps in the headphone out circuit are too small, but they can easily be changed with larger SMD caps to give a full bass response with low impedance headphones if they are too small.

Hope some of you find this information to be useful.

Regards,

Vinnie

 

[unkoman]

Does this mean that line out on color ipods arent "real" line out, since it bypasses through the op amp?

Thanks

 

[Vinnie R.]

Quote:

Originally Posted by unkoman Does this mean that line out on color ipods arent "real" line out, since it bypasses through the op amp? Thanks

No, not at all. There is no "bypassing through an opamp." The output of the Wolfson dac is sent to the opamp to obtain more gain (either voltage gain, current gain, or both).

Many line outs of audio sources (external dacs, cd players, dvd players, etc) use an opamp output stage. I much prefer to take the line out voltage output off of the Wolfson dac an feed it directly to the output
jack (via very high quality coupling caps) so there is less in the signal path (less degradation), but either way is still a line output, designed to drive a line input of a preamp, integrated amp, headphone amp, etc. Usually, the input impedance of such a devices is greater than 10k...but this is not always the case (I've seen some as low as 5k).

The other output is the headphone output, which is designed to drive the low impedance of headphones (ex. 32-ohms). As you all know, this is a variable output with the iPod, while the line-out is a fixed level output...

Regards,

Vinnie

 

[Bob_McBob]

Any thoughts on the low impedance distortion issue? It doesn't come up a lot in regular listening, but some tracks really show it quite painfully, especially solo piano music.

 

[Vinnie R.]

Quote:

Originally Posted by Bob_McBob Any thoughts on the low impedance distortion issue? It doesn't come up a lot in regular listening, but some tracks really show it quite painfully, especially solo piano music.

Hi Bob,

I am not familiar with this issue. Can you provide me with some background on it?

Thanks,

Vinnie

 

[benjamind]

Several individuals complained of audible distortion on their Color iPods obviously due to the video outputs because the distortion seemed to only occur in the higher midrange and treble, but I believe Apple quietly fixed this problem and that anyone who has this problem can easily return their iPods and demand a replacement. The problem, it seems, only occured on low impedance phones (especially canalphones).

When I'm out I'll try the 20gb and 60gb iPod Color and let you know the difference between them regarding sound quality. There may very well be a difference but my ears will ultimately hear the difference.

 

[benjamind]

Vinnie, what are the numbers on the Analog Devices opamps? Are they the new AD8397 opamps or are they a different opamp? Is there a picture somewhere on the web showing the guts of the 60gig Color iPod?

If they're the new AD8397 opamps then they're high quality and they also have their own inbuilt buffers, they are also known to drive low impedance canalphones with authority and with a lot less hiss. So far the AD8397 is really the best opamp for canalphones but the bonus is that it also drives higher impedance headphones quite well too.

Thanks Vinnie,
Ben

 

[Bob_McBob]

There is a rather lengthy post on the issue at the ilounge forums here. If you don't want to read through the whole thing, the gist of the matter is that with low impedance headphones (like the er6is, though the stock Apple buds exhibit it too), there is distortion on high notes from instruments like pianos.

This is limited to the headphone output with low impedance headphones. If I amp it or use high impedance headphones, it's inaudible. The line-out is unaffected. Etymotic has officially acknowledged the problem, and suggests buying their $65 level attenuator to correct it.

I'd be happy even if Apple quietly fixed whatever is wrong, because at least I could be guaranteed a working iPod if I returned my current one. Unfortunately, I haven't seen any convincing evidence pointing to this conclusion.

 

[Vinnie R.]

Quote:

Originally Posted by benjamind Vinnie, what are the numbers on the Analog Devices opamps? Are they the new AD8397 opamps or are they a different opamp? Is there a picture somewhere on the web showing the guts of the 60gig Color iPod? If they're the new AD8397 opamps then they're high quality and they also have their own inbuilt buffers, they are also known to drive low impedance canalphones with authority and with a lot less hiss. So far the AD8397 is really the best opamp for canalphones but the bonus is that it also drives higher impedance headphones quite well too. Thanks Vinnie, Ben

Hi Ben,

The AD opamps have no numbers on them (they are tiny and only have a letter or two on them), but I recognize the AD logo.

I'll take pics soon...

 

[Vinnie R.]

Quote:

Originally Posted by Bob_McBob There is a rather lengthy post on the issue at the ilounge forums here. If you don't want to read through the whole thing, the gist of the matter is that with low impedance headphones (like the er6is, though the stock Apple buds exhibit it too), there is distortion on high notes from instruments like pianos. This is limited to the headphone output with low impedance headphones. If I amp it or use high impedance headphones, it's inaudible. The line-out is unaffected. Etymotic has officially acknowledged the problem, and suggests buying their $65 level attenuator to correct it. I'd be happy even if Apple quietly fixed whatever is wrong, because at least I could be guaranteed a working iPod if I returned my current one. Unfortunately, I haven't seen any convincing evidence pointing to this conclusion.

Hmmmm, sounds like possible oscillation when using low impedance phones. I'll read the link that you sent me. Is this something that was noticed with the 20Gb iPod (black/white), or only the iPod color models?

I'm liking the stock sound of the line out of the 20Gb black/white iPod better than my 60Gb iPod Color, but I'll be modding it soon so they *should* end up sounding the same after mods. I'll post my findings...

 

[unkoman]

Which ipod, the 4G or the color, have more neutral sound out of the line out in your opinion?

Thanks

 

[discord]

Quote:

Originally Posted by Vinnie R. Hmmmm, sounds like possible oscillation when using low impedance phones. I'll read the link that you sent me. Is this something that was noticed with the 20Gb iPod (black/white), or only the iPod color models?

With the color models.

 

[benjamind]

It shouldn't matter whether it's a B&W iPod or a Color iPod, the line out should sound *exactly* the same. If it doesn't, then Apple should seriously reconsider their iPod Color line and release a 5th Gen iPod which should be basically an iPod Color (iPod colors are awesome as they are) but with virtual ground to separate the video signals from the DAC and serious capacitors for the output stage and maybe using a high quality opamp like the one I mentioned above for headphone output, and an absolutely *neutral* line out (that means a direct line straight from the DAC to the line-out socket). That works out to be about $15-20 worth of parts. For an extra $50 at the consumer end, it's sure to be a winner. After all, the purpose of a portable music player is to listen to music! Sound quality and user-friendliness are both major priorities (Apple has certainly done well with the latter, but they need a little extra work on the former - sound quality is important to me and it's important to most head-fiers).

Color screens and other features should be second priority.

 

[Bob_McBob]

There's an example track posted early on in the ilounge thread that shows the distortion problem extremely well. Here's the link: http://www.springpublications.com/pollini.m4a With my er6is, my iPod is unlistenable. With my MS-1s (32 ohm), things are better, but I can still clearly hear the distortion. Have a listen.

 

[Vinnie R.]

Quote:

Originally Posted by unkoman Which ipod, the 4G or the color, have more neutral sound out of the line out in your opinion? Thanks

Hi unkoman,

I prefer the line out of the 20gig, 4th generation iPod (black and white screen) to my 60gig iPod Color.

Hi Ben,

The line outs don't sound exactly the same to me. After tracing out the circuit inside, I found that for the black and white 4th gen iPod takes the line out from the Wolfson dac and sends it to the dock connector. However, the iPod Color has an opamp between the Wolfson dac and the line out. IMO, adding the opamp in the line out sucks.

Anyway, I'm going to bypass and perform the iMod on my 60Gb, but this time I think I can keep everything internal if I convert the headphone out jack to a dedicated line out. The upgraded Black Gate coupling caps should be able to fit in the 60Gb case because it is a little deeper.