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imod dock vs ipod classic dock

post #1 of 15
Thread Starter 
Right, I'm guessing all this should be pretty straightforward, I've read a few threads and I've come to my own conclusions, but I've still been having this debate with a retailer. I'm not naming him because I don't want his name to be dirtied in any way, but I'll put mine (fwiw) on the line.

Basically he maintains that

Quote:
Actually if you can find a thread which Vinnie posted in head-fi about his review on the 6 gen classic against the 5.5 gen, he did mention that there is no caps between the DAC and line out on the 6 gen classic therefore nothing to mod and we all know that imod is all about that. So if that is the case why doesn't the 6 or 7 gen need caps and the imod need?
I'm not sure how the classic works, I read the thread

Quote:
There are also no caps, as this chip is fed a split power supply (+/- voltages), so I'm sure there is a push-pull output stage built into the chip. No measured bass roll-off issues under load. There are only a few tiny surface mount resistors/inductors in the signal path.
which does indicate a very clean path...

at the same time,

Ken has stated so here:
Quote:
If you do not have these dc blocking capacitors in the signal path, your amplifier will be amplifying dc offset voltage, and you run the risk of damaging the dac in your iMod, your amplifier, and your headphones or speakers! Even if you are lucky and this does not damage your equipment, the music will not sound good because your headphone or speaker drivers will always be pushed in one direction due to the dc offset voltage. This also heats the voicecoil of the driver and makes your amplifier work harder.
And Vinnie here:
Quote:
If you try to connect the iMod to the iTransport's analog outputs, you won't have the dc blocking caps in the path (since the iTransport's analog output is a pass-through from the line out dock of the iPod), so you'll have dc offset voltage on the output - this is no good and NOT recommended!


So I'm guessing it's the split power supply in the 6/7G that helps prevent the dc offset from damaging equipment down the line?

Or is he right in saying capless is fine, as long as there's an amp in the path.

Like I mentioned, I think I know what the answer is (please use caps), but I'm hoping for something substantial that can help explain a "proper" position better.
post #2 of 15
PM send.
post #3 of 15
Thread Starter 
Quote:
Originally Posted by Rico67 View Post
PM send.
Thanks for the PM, and yeah, obviously if the amp has caps for DC blocking things will be ok. question is do amps generally have that? If so you're kinda putting 2 caps in serial, which might not be a good thing for the sound?
post #4 of 15
Hi Rico,

If you don't mind, could you PM me your explanation too? Thanks!
post #5 of 15
Hi direcow,

The 6th gen iPod (iPod Classic) is a different animal to the 4G and 5G/5.5G iMod.

With the 4G, 5G, and 5.5G iMod, we take the output directly off of the Wolfson dac chip and feed this to the output. There is dc offset voltage on the L and R outputs from the Wolfson dac. It is important to block this before feeding into a headphone amp (or home audio preamp, or car stereo AUX jack or whatever). Not all electronics block this (and in the worst case, some have dc offset voltage at their input) and this can easily damage the dac chip in the iPod if there are no dc blocking caps to protect it.

With the 6G (iPod Classic), they are using a chip that incorporates the Cirrus dac and the output stage - all in one chip. There is no dc offset voltage, as they use a split supply to feed a section of this chip for the output stage. You do NOT need an iMod dock cable with the 6G (or any stock iPod for that matter) - you can use a standard line-out dock without the dc blocking caps.
The 4G iMod has the dc block caps inside the unit (the black gate caps) because we are able to make them fit and keep the signal path short. For the 5G/5.5G, ALO Audio makes the required iMod dock cable that has these caps installed in the dock plug. ALO also offers iMod dock units, which feature even high quality caps (Auricap, Vcap, Jensen) and in solid wood with high quality jacks, optional charging jack, etc...

Getting back to the 6G...just because the 6G does not need the caps does not mean it is a better sounding unit. Many who have compared the 6G to the 4G, 5G, and 5.5G iMods confirmed that the iMod comes out ahead in many areas... especially when you use the Auricap, Vcap, or Jensen cap dock with the 5g/5.5g iMod.

For those who decide not to use the iMod dock for the 5G/5.5G iMod (which has the dc blocking caps), that is your choice and if your dac fails, this is not in warranty and you will need to pay for a new motherboard and the costs to mod the iPod again. If your headphone amp amplifies the dc offset voltage and feeds this to your headphones, it is going to overheat the voice coils of the drivers. If that does not damage them and cause them to fail, at the very least it is NOT going to sound like the iMod because how can you expect your drivers to sound good if they are always being pushed in one direction (by the DC voltage) while trying to vibrate?

Quote:
So I'm guessing it's the split power supply in the 6/7G that helps prevent the dc offset from damaging equipment down the line?
All of the stock iPods do NOT have dc offset voltage on their outputs. For example the 4G and 5G stock iPods have opamp output stages with dc blocking caps. They are not very good caps and I don't care for the sound of these output stages in the path (and removing that is what the iMod is all about). The 6G has a different output stage (built into the Cirrus CODEC chip) and again, there is no dc offset voltage. And the 7G is just like th 6G iPod Classic, but with a 120GB hard drive - unless there are other differences?

So ALL the stock iPods have no dc offset voltage. It is only with the 4G, 5G, and 5.5G iMod that this needs to be addressed. Again, in the case of the 4G, this is addressed inside of the unit. In the case of the 5G/5.5G, the ALO iMod dock cable (or wooden iMod dock) addresses it.

I hope this post helps clear things up!

Vinnie
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post #6 of 15
Thread Starter 
Thanks for the detailed post vinnie... Just the expert I'd need to hear from

Cheers!
post #7 of 15
Pretty good info. Well over my head in technical details.
post #8 of 15
Thank you for the information
post #9 of 15
Hi Ken, just wondering is it save to plug the imod to vcap dock all the time? Will imod use power from the power cord and the battery be bypassed after fully charged? Thanks!
post #10 of 15
Vinnie,

are there any amps which safely pair to iMod without blocking caps? I am especially interested to know about following:
  • Pico
  • Supermicro IV
  • Minibox E+
post #11 of 15
Quote:
Originally Posted by Jian View Post
Hi Ken, just wondering is it save to plug the imod to vcap dock all the time? Will imod use power from the power cord and the battery be bypassed after fully charged? Thanks!
Hi Jian,

Yes, it is safe to keep it plugged into the AC power. It will keep your battery fully charged as well as draw its power from the 5V power adapter.

Quote:
are there any amps which safely pair to iMod without blocking caps? I am especially interested to know about following:

* Pico
* Supermicro IV
* Minibox E+
Hi kostalex,

I do not recommend using the 5g/5.5g iMod with an amp without using the ALO iMod dock cable or iMod dock unit (which has the dc blocking caps).

You run the risk of damaging your iMod's dac (which would require a complete motherboard replacement), your headphone amp, and even if your headphones.

Best regards,

Vinnie
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post #12 of 15
Thank you for the explanation.

I have another question of using both iMod (Gen4) and iPod (Gen6) with the same iMod Dock.

I have no doubt that my iMod G4 + iMod Dock will be a great pair, but how about using iPod G6 with the same dock?

The sound quality from iPod G6 + iMod Dock will be better than universal dock (or Dock to RCA cables) or it will drop the quality (to the level of noticable)?

Thanks for your advice.
post #13 of 15
Quote:
Originally Posted by smart View Post
Thank you for the explanation.

I have another question of using both iMod (Gen4) and iPod (Gen6) with the same iMod Dock.

I have no doubt that my iMod G4 + iMod Dock will be a great pair, but how about using iPod G6 with the same dock?

The sound quality from iPod G6 + iMod Dock will be better than universal dock (or Dock to RCA cables) or it will drop the quality (to the level of noticable)?

Thanks for your advice.
Hi Smart,

The 4G iMod has BG caps installed in the ipod body and outputs to the headphone jack. The dock audio out is not functional so a dock is not an option.

The 6G classic will not benefit from a iMod dock or cable.

We have a iMod FAQ HERE.

Thank you
Ken
post #14 of 15
Ken, Vinnie,

why do not you imod Mini? Is it inferior to 5.5G in terms of SQ?
post #15 of 15
Thank you, Ken.
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