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Old 24th November 2011, 06:43 PM   #831
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Originally Posted by ethanolson View Post
So I'd basically have to cut the design in half (one 4556) and make sure my gain is under 2x, right? That would keep me way under that level... or am I wrong? My cans need up to 125mW at 55 Ohm to ensure I can listen to some really good classical. My reason for wanting the upper limit is because I have young kids in the house who are starting to like listening to my cans. My son almost blew my cans to pieces with my current amp because it can deliver ~600mW into my AKGs which are rated to 200mW.
This wouldn't work, one 4556 is used per channel (L,R) in parallel to increase the power output. You run one chip and all you do is lose one channel.

Your best bet, if you're really concerned, would be to just use unity gain and leave out the gain resistors entirely. You could try to diy some type of stop to limit the volume pot travel as well.

Last edited by shadow419; 24th November 2011 at 06:46 PM.
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Old 24th November 2011, 07:21 PM   #832
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How would I go about modifying the O2 to ensure I can't exceed 200mW into 55Ohms (really 55-125 Ohm according to measurements)?
As has already been suggested, just use 1X gain (or possibly more depending on your source). Very few sources put out much over 2 Vrms. With 1X gain that's only 72 mW into 55 ohms and 32 mW into 125 ohms.

Or, working backwards, 200 mW at 55 ohms is 3.3 Vrms. If you know the highest output source you'll be using, set the gain at 3.3/Vsource. With a typical 2 Vrms home Redbook-compliant source, that's 3.3/2 = 1.6X gain. With an iPod LOD, however, it's 3.3/.5 = 6.6X.

If you're worried about accidents, use the above gain for the High Gain setting and have the Low Gain option be less or the same.

That way, even at full volume, playing a track hitting 0 dBFS, you can't get more than 200 mW out of the O2 into 55 ohms (and less power into higher impedances).
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Old 24th November 2011, 07:49 PM   #833
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Originally Posted by Robes View Post
How far are we away from a desktop version of the O2?

Any early info to share?
Some of this may be old news to some, but the official name is "ODA" for Objective Desktop Amp. There's some early info, if you haven't seen it already, towards the end of the O2 Summary article (under "WHAT ABOUT A DESKTOP ONLY VERSION?").

In addition to what's linked above, the latest news is the ODA DAC daughter board. As I've mentioned in this thread, the current plan is for a relatively simple, small, single board USB DAC option that supports true high-resolution 24 bit audio at native 44, 48, 88 and 96 Khz over USB (something relatively few DACs can do regardless of what 24/192 DAC chip they use and virtually no DIY DACs support 24 bit USB).

The DAC complies with the USB Audio standard and hence has native driver support, even at 24/96, built into Windows, OS X and presumably Linux. This is in contrast to most high resolution pro audio interfaces, and the open source AVR-based DIY DAC, that require proprietary drivers.

The DAC board will "piggy back" on top of the headphone amp board as a daughter card and there will be a switch to select the line input or DAC as the source.

I'm currently testing the DAC board and it offers well in excess of 16 bit performance (many "24 bit" DACs don't) providing a significant benefit for those using software volume controls compared to a 16 bit USB DAC. It also has very low jitter and respectably low distortion. Like the O2 and ODA, it's a minimalist design focused on maximum performance for the lowest cost.

As previously mentioned, for programming, licensing, testing, and SMT reasons, the DAC daughter board will only be sold pre-assembled (but not by me and I will not receive any revenue or profit). So you can build your own ODA and then just solder the DAC board on top.

For those wondering why not full DIY, there are no USB solutions that I know of supporting 24 bit operation that can be purchased and used off-the-shelf in a DIY project without requiring at least programming. And the better solutions are only available under license and/or other contractual agreements. That makes a full DIY DAC very difficult as DIYers can't buy the chips, and even if they could, they require proprietary programming before use. The only exception I currently know of is the AVR solution already mentioned but even it requires programming and extra hardware to do so. It also requires a proprietary driver for use.

I'm hoping to publish the first ODA article and start the first thread here in diyAudio in the first part of December (the next few weeks).
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Old 24th November 2011, 08:01 PM   #834
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You sir, are a genius!
I really enjoy your articles, even though the cheapo-DAC's are not really my category of interest.
Lookin' forward to the ODA articles though...
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Old 24th November 2011, 08:12 PM   #835
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RS!

"The only exception I currently know of is the AVR solution already mentioned but even it requires programming and extra hardware to do so. It also requires a proprietary driver for use."

No HW needed for programming (ISP), Linux and our Apple friends already have UAC2 built in (no need for drivers) it's only us occational Windows users that have to reely on UAC1. So the Audio-Widget is about what we need... CD quality can be darn good if you choose the right productions!

Even 320kps mp3's is almost quite ok listening to IF the source if of quality...
I'm actually listening to Hans Theessink - Call me - amazing (mp3-320)... I have to buy his CD's or better!

My feeling is that we need to crunch this nut regarding MS reluctance to create a common driver. Now how would we do that? I sent a request to MS about it and got as an answer that MS doesn't do HW so the driveras are of the HW manufacturers concern, not MS. But they kindly hinted about a thread in, now it stands still in my head, the MS dev site - now what it is named?
There is probably things going on inside MS as well - they have a UAC1 common driver so why not a a UAC2 one? Everyone else has one built in...

So the Audio-Widget guys are on the right track IMO.

Brgds

Last edited by Turbon; 24th November 2011 at 08:32 PM.
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Old 24th November 2011, 08:22 PM   #836
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@Turbon, around 90% of the desktop/laptop PCs on the planet are running Windows. So, yeah, a tiny minority may not need drivers That will slowly change depending on how quickly Win8 is adopted (or perhaps Microsoft will release UAC2 Win7 drivers as part of an update).

ISP does require hardware--it either has to be built onto the board, or outboard like the AVR-ISP from Atmel. Your average analog audio DIYer isn't set up for MCU programming. Or can the design use a factory USB-based bootloader?

For those who are comfortable working with microcontrollers, and don't mind a "2 box" or custom enclosure/packaging, the AVR design is a more flexible option. But I really doubt it will sound any better. It also may cost more than the ODA DAC board--certainly with both in assembled form.
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Old 24th November 2011, 09:00 PM   #837
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Now RS. Of course when reaching the greater public outside of nerdy sites as diyaudio the widget has the latest driver in memory ready for windows and info for windows update about where to find the latest... But this won't be needed since MS is going to release a UAC2 common driver - the question is how much badwill they are prepared to draw upon themselves over this before release...

I'm not selling anything and will of course with great pleasure try whatever you decide to be the best companion for the O2. The fear I might feel is that the DAC isn't usable to it's full potential outside of Windows...
On the other side You doesn't seem to be one of the evil ones and I run windows whenever I feel to or have to (every day :-) ).

Brgds / Nerd and proud of it...

Last edited by Turbon; 24th November 2011 at 09:11 PM.
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Old 24th November 2011, 09:24 PM   #838
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The fear I might feel is that the DAC isn't usable to it's full potential outside of Windows...
The ODA DAC should work equally well in Linux, OS X and XP or later as it's based on USB Audio 1.x. Point taken about geeks being more likely to run Linux but I'm sure OS X and Linux combined are still a minority even here on diyAudio.
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Old 24th November 2011, 09:30 PM   #839
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Now of course we/they are RS.

So we are expecting 24/48 as maximum? Well, it aint bad with the right source :-)

BTW, I'm not going to give any benefits, cash payments or be at any help for those who should show an intrest in in using anything outside of windows regardless that I know that you and only you have to cross that white line painted on the highway. Not everyone is ready for that shift of mind. I'll setle for using whatever that suits me best for the job.

Brgds / Occational Geek

Last edited by Turbon; 24th November 2011 at 10:00 PM.
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Old 25th November 2011, 01:54 AM   #840
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So we are expecting 24/48 as maximum? Well, it ain't bad with the right source :-)
UAC1 supports 24/96 and so will this DAC.

One thing I'd like to mention is that, last I knew, Windows adjusted the native audio feed bitrate on a song by song basis so that nothing had to be soft-scaled as long as the DAC supported it. I believe Mac doesn't do that yet. Where does Linux stand?
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