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LOD question I am embarrassed to ask

post #1 of 38
Thread Starter 
Please be merciful, I HAVE tried the search function but everyone here seems to understand this already... everyone except me. LOD's seemed to come into major use while I was away from headfi, so I need some help now...

Please tell me, what does a LOD cable do exactly? I read that it does not bypass the internal ipod amp. And I know it does not bypass the internal ipod DAC. I don't understand what kind of signal goes out of the ipod dock-plug-part, so I do not understand what is the function and advantage of using a LOD.

I'm sure this can be cleared up quickly... please enlighten me! It's driving me crazy! I'm the only person here who does not understand this!

Thank you.
post #2 of 38
Can't answer the question in a technical way, as I'm thick as a brick, but as far as I understand it, the line out connection gives the most direct path for the music signal from a player's internal DAC to the headphones. The headphone socket in many cases is actually at the end of a somewhat obstructed pathway, so sound quality can suffer compared to the purer route offered by a line out.

In the case of the iPod, for example, I'm using a 6th gen Classic and have a line out cable feeding my headphone amp, and it sounds noticeably cleaner and more powerful than if I hook my amp up to headphone output.

Of course, the iPod is still outputting an analogue signal, so the unit itself is processing the digital signal internally before it reaches the headphone amp - meaning the signal is only ever going to be as good as the iPod's own inbuilt DAC. Conversely, there are some players which provide digital line out connections as well, which allow you to link a dedicated DAC in the chain an improve the sound even more.

Thats my take on it all anyway, and I might be completely off the mark.....
post #3 of 38
A LOD takes the fixed (ie: the volume not controllable from the iPod) analogue signal from the iPod and allows it to be connected to an amplifier of some sort.
post #4 of 38
Thread Starter 
Quote:
Originally Posted by Currawong View Post
A LOD takes the fixed (ie: the volume not controllable from the iPod) analogue signal from the iPod and allows it to be connected to an amplifier of some sort.
Ok this is becoming clearer, but isn't it true that there is some kind of amplifier within the ipod itself, and the LOD cannot bypass that amp? or is what I read wrong, and the LOD takes a completely unamped analog signal out to the external amplifer.

?

thanks again
post #5 of 38
Quote:
Originally Posted by spinneresque View Post
Ok this is becoming clearer, but isn't it true that there is some kind of amplifier within the ipod itself, and the LOD cannot bypass that amp? or is what I read wrong, and the LOD takes a completely unamped analog signal out to the external amplifer.

?

thanks again
I'd say there has to be some amplification, because the signals out of a DAC chip are pretty small and aren't line-out level.
post #6 of 38
Thread Starter 
Right... so if you are not bypassing the amplifier using the LOD, and you are not bypassing the DAC, then at what point in the ipod's processing does the LOD come in?

Am I making sense? I guess there would be the Dac's little amp plus an additional headphone amp and the Dock output cuts into the signal before it hits the headphone amp/ output?

???
post #7 of 38
This LOD talk begs the following question to me - is there such a thing as a portable player that can provide a purely digital signal out? Then the D to A conversion and subsequent amplification would be done *only* by the headphone amp? That would seem cool, because then the portable would be nothing more than a storage device.
post #8 of 38
I was under the impression that the Ipod connection has pins that allow access to the digital information which can be used to bypass the Ipod DAC. I believe that is how the Wadia transport works - see link to the description on the Crutchfield site: Wadia 170iTransport iPod® dock with digital output at Crutchfield.com
post #9 of 38
Quote:
Originally Posted by spinneresque View Post
Right... so if you are not bypassing the amplifier using the LOD, and you are not bypassing the DAC, then at what point in the ipod's processing does the LOD come in?

Am I making sense? I guess there would be the Dac's little amp plus an additional headphone amp and the Dock output cuts into the signal before it hits the headphone amp/ output?

???
ok, let me try this. the ipod is a pretty low voltage device right? even the line out needs some form of buffering to provide a decent output level. thus is not the same as taking the signal from the HP out. the HP out also has to go through several more components on its way out, including the volume control circuit (internal to the dac). the HP out turned up full and LO are NOT the same level, they are not the same. also the output impedance from the LO is lower and there is more capacitence in the HP out to deal with lower impedance loads

i'm not even sure this applies to all ipods. for instance the wolfston WM9741/1 has an internal I/V stage, likely the same is said for the dac in the ipod video. so yes the signal is probably the same signal. but there are still differences in the 2 signals at the outputs. not sure about the cyrus
post #10 of 38
Quote:
Originally Posted by FlatNine View Post
This LOD talk begs the following question to me - is there such a thing as a portable player that can provide a purely digital signal out? Then the D to A conversion and subsequent amplification would be done *only* by the headphone amp? That would seem cool, because then the portable would be nothing more than a storage device.
Sony PCMD50 has optical out.

Here is another one:
WAVE PlAYER WITH I2s & SPDIF TO DAC NO NEED USB PC-LINK - eBay (item 320432131519 end time Mar-04-10 07:03:16 PST)
post #11 of 38
Quote:
Originally Posted by ldaustin View Post
I was under the impression that the Ipod connection has pins that allow access to the digital information which can be used to bypass the Ipod DAC. I believe that is how the Wadia transport works - see link to the description on the Crutchfield site: Wadia 170iTransport iPod® dock with digital output at Crutchfield.com
I looked at that link and according to the writeup, you are correct. So - is there such a thing as a connector or cable for an iPod that has the iPod connection on one end, and a USB on the other? That way, you could connect the output to a portable amp with DAC, like the 3Move or whatever.
post #12 of 38
Quote:
Originally Posted by nlhk View Post
Thanks nlhk - we were writing our posts at the same time. Is this product the only one of its kind?
post #13 of 38
Quote:
Originally Posted by FlatNine View Post
That way, you could connect the output to a portable amp with DAC, like the 3Move or whatever.
Not quite. Wadia probably has a special chip to allow for that kind of digital out. A connector simply won't do it since iPod dock connector doesn't allow for that kind of operation, not to mention it has no USB host function so it can't output USB signal to DAC amp like the Meier MOVE series.
post #14 of 38
Quote:
Originally Posted by FlatNine View Post
Thanks nlhk - we were writing our posts at the same time. Is this product the only one of its kind?
There are some others with both digital and analog outputs. But with digital output only, I only found this one.
post #15 of 38
An ipod contains a memory to store the music files, a DAC to convert the digital files to analogue and an amp to boost that analogue signal.

If you plug headphones into the headphone jack, or use a dock into the docking port you use all three parts of the ipod to get your signal. Volume control is with the ipod and any amp it is connected to.

If you connect to an ipod with a LOD you bypass the ipods amp only. That way you can do all the amplification and volume control with whatever amp you connect the ipod to. That can be a mini portable amp or hifi amp. Even Apple staff admit that is better than the ipods own amp.

If you connect the ipod by its docking port to a digital dock such as the Wadia itransport or Onkyo NDs1 then it bypasses the ipods amp and DAC and uses it as a memory only to store music files. Both of those docks then need to be connected to a DAC and the DAC to an amp.
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