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The Objective2 (O2) Headphone Amp DIY Project
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Old 29th November 2011, 03:50 PM   #951
ethanolson is offline ethanolson  United States
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Thanks for the responses everyone. These ESS DACs still have some mysteries that I'd love to see unravaled in the future.


Moving back to the O2...
Does anybody know of a source for the battery technology used by Sanyo for the Eneloop 1500 cells that can be adapted to the O2 and still fit in the enclosure?
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Old 29th November 2011, 04:08 PM   #952
qusp is offline qusp  Australia
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Quote:
Originally Posted by RocketScientist View Post
I was (perhaps mistakenly) answering the question in general terms not for a specific DAC. I certainly wasn't trying to criticize any specific designer. Ethanolson's question was:

"Why does everyone have I/V stages for their ESS DACs?"

Because ESS doesn't make their datasheets public I've only seen data on a few ESS DAC chips. But the ones I've seen have an output stage built into them and their DNR spec is at the output pins of the chip--not after an external IV stage as you suggest. The application circuit in the datasheet does not show an op amp stage after the DAC.

Adding an op amp onto a DAC that already has an internal output buffer stage isn't likely to improve much besides perhaps the ability to drive unusually low impedance loads or provide a higher voltage output if desired. Adding gain after such a DAC isn't likely to improve the DNR as you suggest.

Certainly if a DAC chip is designed to be followed by an IV stage, or has a high impedance output, you should use an op amp stage. And it may well be some of the ESS chips are in that category. I was assuming Ethanolson was referring to the ones with built-in output buffers.
ok, lets just leave that then, maybe i was too sensitive there, but as it was a question directed at me specifically and you intercepted it and made that comment it didnt sit right. but lets move on

actually you can quite easily get the DS, just email the distributor its not under NDA anymore, but its still not posted publicly. i got it when it was still under NDA, not sure if i'm still bound or not, but i wouldnt think so, i certainly hope so ha.

no its a bit of a weird one, the same output can be used as current out with higher performance, but puts out varying degrees of voltage depending on the Z it sees at the output. opc/we manage to get ~115db THD +N from literally a couple of mosfets and resistors plus a cap in the signal path, of course there are some other components for setting bias and decoupling, but no magic. i wouldnt say an opamp is necessarily needed, but not being one to avoid them like the plague i also appreciate a well done opamp IV on the sabre too.

its not really that mysterious and the DS doesnt hold that many secrets, certainly nothing you cant see around the forum. some might call it a flaw that the output is so easily wavered. it certainly is a bit touchy with that, the quality of the i2s and quality of the somewhat complex power supply arrangement, but if you can get it right its superb.

anyway, apparently my O2 pcbs are actually on their way as of today!! haha

Last edited by qusp; 29th November 2011 at 04:11 PM.
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Old 29th November 2011, 04:25 PM   #953
sofaspud is offline sofaspud  United States
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Quote:
Originally Posted by sgrossklass View Post
"Amped" is far too general a term though. An amplifier is, after all, not a magic black box that'll make cans sound better no matter what. That's not how things work in the real world. And whenever "better" comes up, the inevitable question arises - compared to what? Headphone outputs vary widely, too.
Too general? Not really. I was speaking of the general population, for example the proliferation of iPod/iPhone users I've been seeing with their "Dre b's" or whatever they call them, or the earbud/mp3 player crowd.
Quote:
Ultimately it comes down to analyzing a headphone's needs (required voltage and current levels, tolerable noise and output impedance) and matching that to whatever the source has to offer. If this works out well across a wide range of headphones, we have a good amp there.
For audio geeks and diy crowd, sure. General population don't much care. That's the real world.
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Old 29th November 2011, 05:26 PM   #954
Shamharoth is offline Shamharoth  France
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Hello, I'm about to build my O2 but I have several questions :
- Is there any schematics for the front panel ? The FPE software keeps crashing so I would like to just have some measures...
- RS recommends using "pigtail" style adapter for connecting 1/4" jack. But I can't seem to find these anywhere. Do you know where I can get one ?

Thank you
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Old 29th November 2011, 05:32 PM   #955
4nradio is offline 4nradio  United States
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Quote:
Originally Posted by Shamharoth View Post
Hello, I'm about to build my O2 but I have several questions :
- Is there any schematics for the front panel ? The FPE software keeps crashing so I would like to just have some measures...
- RS recommends using "pigtail" style adapter for connecting 1/4" jack. But I can't seem to find these anywhere. Do you know where I can get one ?

Thank you
Hi Shamharoth,

You can see a photo of the front panel I had made for my O2 by looking at the pic in message #784 in this thread.

There is a link to download the FPD file in message #794. You could send this file directly to Front Panel Express without you having to open it (assuming you don't want to make any changes).

BTW, I was very impressed with the accuracy of machining of the panels by FPE... the fit and finish was perfect. I look forward to seeing their facilities during a Seattle area Head-Fi meeting in January.

Last edited by 4nradio; 29th November 2011 at 05:37 PM.
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Old 29th November 2011, 06:31 PM   #956
Shamharoth is offline Shamharoth  France
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Quote:
Originally Posted by 4nradio View Post
Hi Shamharoth,

You can see a photo of the front panel I had made for my O2 by looking at the pic in message #784 in this thread.

There is a link to download the FPD file in message #794. You could send this file directly to Front Panel Express without you having to open it (assuming you don't want to make any changes).

BTW, I was very impressed with the accuracy of machining of the panels by FPE... the fit and finish was perfect. I look forward to seeing their facilities during a Seattle area Head-Fi meeting in January.
I can't open any FPD file, the software keeps crashing. I tried to uninstall and reinstall it, but to no avail.
I would like to build the front panel myself as I have the required tools (and would like to save some money too ), but I need to have some dimensions to work with. Or maybe someone can export the FPD file at the correct scale to PDF (A4 paper) ?

BTW, your panel looks great!
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Old 29th November 2011, 06:40 PM   #957
RocketScientist is offline RocketScientist  United States
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Quote:
Originally Posted by Shamharoth View Post
Hello, I'm about to build my O2 but I have several questions :
- Is there any schematics for the front panel ? The FPE software keeps crashing so I would like to just have some measures...
- RS recommends using "pigtail" style adapter for connecting 1/4" jack. But I can't seem to find these anywhere. Do you know where I can get one ?
You might try a different PC for the FPE software as I've never had it crash or heard of it crashing. Unfortunately the software doesn't have dimensioning otherwise I could just produce a PDF from FPE.

The coordinates for the openings are in the O2 PDF on the board drawing as measured from the center of the board and from the top surface of the board.

I also know JDS Labs is working on selling a pre-machined panel, and you probably saw the link to the thread on the laser cut acrylic panels.

The 3.5mm to 1/4 inch "pigtail" adapter can by anything similar to the HOSA YMP233 (which happens to have dual 1/4" jacks):

http://www.amazon.com/HOSA-STEREO-3-...dp/B000068O5I/
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Old 29th November 2011, 06:54 PM   #958
Shamharoth is offline Shamharoth  France
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Quote:
Originally Posted by RocketScientist View Post
You might try a different PC for the FPE software as I've never had it crash or heard of it crashing. Unfortunately the software doesn't have dimensioning otherwise I could just produce a PDF from FPE.

The coordinates for the openings are in the O2 PDF on the board drawing as measured from the center of the board and from the top surface of the board.

I also know JDS Labs is working on selling a pre-machined panel, and you probably saw the link to the thread on the laser cut acrylic panels.

The 3.5mm to 1/4 inch "pigtail" adapter can by anything similar to the HOSA YMP233 (which happens to have dual 1/4" jacks):

http://www.amazon.com/HOSA-STEREO-3-...dp/B000068O5I/
Thank you. I'll try using using the coordinates on the board schematics.
edit: the software worked on another computer, so everything's fine.

For the adapter I didn't even think to look on amazon, silly me.

Last edited by Shamharoth; 29th November 2011 at 07:07 PM.
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Old 29th November 2011, 07:21 PM   #959
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by RocketScientist View Post

The 3.5mm to 1/4 inch "pigtail" adapter can by anything similar to the HOSA YMP233 (which happens to have dual 1/4" jacks):

Amazon.com: HOSA STEREO 3.5mm PHONE (M) - TWO STER. 1/4" PHONE (F), 6 in.: Electronics
I suggested a HOSA adapter to my buyers, and one of them had issues with their build quality.. Another option is this one, which I believe is made by Sennheiser.. Adapter 1/4 to 1/8 in 3.5mm fit SENNHEISER HD 518 HD518 | eBay
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Old 29th November 2011, 08:15 PM   #960
RocketScientist is offline RocketScientist  United States
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Thanks MrSlim! That indeed at least looks like the one that came with my HD650s which is a well designed, and well made, adapter.
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