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LOD makes no sense for iPhone/Touch (?)

post #1 of 41
10/1/08 at 8:06am
Thread Starter 
Hi everybody,

I just browsed the web for the audio components of the iPhone/iPod Touch and found that everything is done by the Wolson WM8758. I could only find a datasheet of the WM8750, but I suppose that they are mostly identical.

Interestingly this chip only has one speaker output and one output that is used for BOTH Headphone and Line out. According to the datasheet no other components are needed and a look at the PCB of the ipod touch shows that there probably is no space for other components that could influence the headphone out.

This would mean, that the LOD-Connector is not better that the headphone out for the iPhone/Touch! Is this true?
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post #2 of 41
10/1/08 at 9:23am
Yes the dac chip has two outputs, but the weakness is the amplification circuit used for the headphone output. People use the portable amplifiers and LODs to bypass that internal amplifier.
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post #3 of 41
10/1/08 at 10:42am
Thread Starter 
No, as far as I understand the Wolfson has a headphone amp on board. So there actually seems to be no external amplification, the output of the codec chip goes directly to the headphone jack.
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post #4 of 41
10/1/08 at 11:29am
Quote:
Originally Posted by claus View Post
This would mean, that the LOD-Connector is not better that the headphone out for the iPhone/Touch! Is this true?
My experience with my 5.5 iPod is that using the line-out results in better SQ when I hook up to my home audio system than when I use the headphone jack for output. I can't say for certain that line-out is better SQ per se, but it could be the voltage/current of LO is better suited to line-in.
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post #5 of 41
10/1/08 at 11:35am
All I know is I detect a difference in sound quality. I just did a comparison of the HP out and LO and the LO has crisper, cleaner sound. It's detail...not more detailed, I mean detailed, period. The HP out isn't detailed. I didn't run the HP out to the amp because I currently have no min - mini.

If there is no internal amplification going on, something else, like the volume control circuit, is making a difference in sound quality.

Everyone with an iPod dock and home stereo can test the difference in sound quality very easily through there headphones. Simply connect the iPod dock to a stereo which has HP out and listen.
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post #6 of 41
10/1/08 at 5:35pm
Thread Starter 
Hm, being a stubborn objectivist I hesitate to believe my ears when it comes to such subtle differences in sound quality, at least in a non blind comparison. But I fully agree that listening is probably the only reasonable test. Even when there are theoretical differences in quality I do not care if I am not able to hear them with my equipment :-). I will see if I am able to set up a blind test for this...

But I would expect that this is something somebody probably already has looked into. My search in the forums for ipod and lod unfortunately brought up a gazillion of posts which I will never be able to dig through.

I think that the mechanical quality of headphone jack and plug is superior to the quality of the iPod connector, so if sound quality would be comparable, I think the headphone plug would be my first choice.
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post #7 of 41
10/1/08 at 6:09pm
Claus,
I have tried the iPhone through the HP and through the LO with my micro, and that horrible static is gone through the LO. IMO the sound quality also benefits from this.
I do not know about the circuit itself, but there is that nasty software potentiometer in the iPhone that is bypassed with the LO.
Dave
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post #8 of 41
10/2/08 at 12:15am
I tried the ipod touch with both LO and HP, and I think that there is a significant difference. If you're using revealing headphones, I think it's pretty noticeable. Using my Etys, it really stood out.

For general listening though, I usually use UM2s with custom molds. While not quite as detailed as the Etys, the difference is still noticeable. I'll use the HP out if I'm just listening to a podcast or watching a movie. Otherwise It's line out and my Xin Mini-IV all the way.

-Jeff
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post #9 of 41
10/2/08 at 3:51am
Thread Starter 
Thank you all for your answers and for bearing with my scepticism, but I am still not convinced...

myinitialsaredac: The Wolfson chip has an on-chip digital volume potentiometer, which I suppose is used for the iPhone volume control. This poti is always in the signal path, but will not degrade sound quality if the volume is set to maximum. But it will definitely increase the noise floor when not on maximum. Did you compare with volume set to max?

JeffS: I also have Etys (ER4-P), although I have an AMB Mini3 headphone amp. I will do some tests on the weekend and will see if I can reproduce your listening impressions.

BTW: if anybody is interested in the lengthy Wolfson datasheet, it can be found here:

http://www.wolfsonmicro.com/uploads/.../en/WM8750.pdf
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post #10 of 41
10/2/08 at 4:12am
Thread Starter 
Hi everybody! Ok, after some first listening impressions I now might be a believer in the LOD again.

The headphone out on my ipod touch has a much lower level than the line out (I have to say that I have a European version, it might be that this is different for other countries). If my assumption is correct, that both outputs are actually the same, this means that for the headphone out the digital volume of the Wolfson chip is not on maximum, even when the volume control on the ipod is on maximum. This would explain a higher noise floor and dependent on the exact implementation of the digital volume control also other sound degradations.

Unfortunately this difference in volume makes it even harder to make a blind comparison. I will keep you updated about my attempts...
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post #11 of 41
10/2/08 at 11:13am
Does the Apple Universal Dock not equal the same as a LOD cable? I have a 2G Touch and when I have it in the dock, using a mini->RCA line-out on the back of the dock going out to my Travagan's Red amp, I cannot tell any difference in the sound, at all. In fact, it seems a little less rich and detailed to me over the HO, which sounds superior (if slightly).

I have a custom made LOD that I used with my iPod 5.5G Video, and I could tell a massive difference when using the LOD->Travagans->headphones. (in both cases, the headphones are Denon D2000's). The difference was highly noticable, but with the dock->amp->Denon under the Touch it is like I say above.

The only thing I can think of is that the Apple Universal Dock is not acting the same as a LOD cable, in which case I need to get one of those for my Touch (since the custom TURBO-made one I have now doesn't work with the Touch).

One other point, when using the Apple Dock I still have volume control on the Touch itself in addition to on the amp. This wasn't the case with my 5.5 iPod, the volume control was totally bypassed when using the LOD cable.
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post #12 of 41
10/2/08 at 11:19am
Just a guess, but I'd say that technically, the Apple dock is merely using the HP out. The volume control is a clear sign, as well as the SQ difference.

If you find an affordable (do they exist) LOD cable for the Touch 2G, let me know. I'd like to get one. This is my first Apple DAP, and I know the LODs from ALO and others are expensive. May have to bite the bullet though, cause I like the idea of maxing the SQ.
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post #13 of 41
10/2/08 at 12:58pm
Quote:
Originally Posted by tstarn06 View Post
Just a guess, but I'd say that technically, the Apple dock is merely using the HP out. The volume control is a clear sign, as well as the SQ difference.

If you find an affordable (do they exist) LOD cable for the Touch 2G, let me know. I'd like to get one. This is my first Apple DAP, and I know the LODs from ALO and others are expensive. May have to bite the bullet though, cause I like the idea of maxing the SQ.
This is what I was afraid of. I wanted a dock to sit my Touch in at work. Oh well, the hunt begins for a LOD that isn't ludicrously overpriced. A board member named Turbo created my last LOD, and I know there are a few around that do, and it was reasonably priced.

Can anyone confirm that has used a 2G Touch with a LOD cable that it bypasses the volume controls?
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post #14 of 41
10/2/08 at 5:48pm
Thread Starter 
Interesting. With my Touch 1G and a LOD I can not control volume. I suppose the digital volume control is in charge when using the Universal Dock because as far as I know you can control the volume with the included remote control. The question is probably, if the maximum volume is really the unimpaired signal, or like the headphone out already a lower level signal.

Does anybody have a Universal Dock and a LOD and can compare the output level of both? If they are the same, the Universal dock should probably have the best possible SQ, but I suspect that the Universal Dock provides a lower level.

I did some first measurements and the level of the headphone out seems to be about 7dB lower than the output of the line out (probably resulting in 7dB lower SNR).
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post #15 of 41
10/2/08 at 7:18pm
yeah, by just saying that the universal is controlled by volume makes no discoveries, only conjecture. with my touch, it is a volume-strict line out. also, there is little to no hiss at all with 1g touch. with 2g touch as well.

the volume control on the ipod is not an analogue device which controls the amp, it is a digital multi-function device. so if the volume changes with the apple circle thingy on the dock, it can merely be an attenuator. the sound is quite different if you listen closely, so i will definately call it a line out. not that it matters much to me: they both sound good.
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