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Old 22nd December 2011, 03:04 PM   #1611
Alexium is offline Alexium  Ukraine
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Quote:
Originally Posted by RocketScientist View Post
the best performance will be achieved with the manufacture's reference design.
Initially I thought so too. Then I asked a question on another DIY forum, and gurus of DAC building criticized the reference schematics all they could, saying it's only designed to achieve high S/N and dynamic range. I'm not sure if they are right or not, but they do know something about DACs (and I don't), so they made me doubt.
P.S. I know passive I/U is definitely worse than op-amp based one, I just wonder if I can hear any difference at all. Besides, it's so simple, how can I not try it?

Last edited by Alexium; 22nd December 2011 at 03:15 PM.
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Old 22nd December 2011, 03:55 PM   #1612
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@Alexium, while there are some genuine gurus lurking around in DIY audio, the vast majority have very little objective evidence to back up their claims. They don't run proper blind listening tests and they lack the right test equipment to verify their claims and designs. Instead, nearly all use highly biased and flawed sighted listening. See: Subjective vs Objective

And, for what it's worth, I don't even consider myself an overall guru. I mostly leverage the work of the genuine gurus--guys like Doug Self, Bob Cordell, Bruno Putzeys, Ethan Winer, Samuel Groner, Walt Jung, etc. All of them back up their claims with credible measurements, blind listening tests, peer reviewed AES papers, engineering calculations, etc. I would suggest looking for genuinely objective evidence supporting claims about I-V stages, or any similar topics. If there is no such evidence, you may want to consider why not?
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Old 22nd December 2011, 04:18 PM   #1613
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is ODA(C) going to come out this december?

Last edited by idjoel2000; 22nd December 2011 at 04:20 PM.
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Old 22nd December 2011, 04:29 PM   #1614
Alexium is offline Alexium  Ukraine
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@RocketScientist, makes sense. By the way, thanks for the Subjective vs Objective article! I've really enjoyed reading it.
During your work on ODAC, have you, by chance, come across any useful articles/blogs/posts/etc. on DAC design that you can recommend to a novice?
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Old 22nd December 2011, 04:53 PM   #1615
qusp is offline qusp  Australia
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yeah RS got it in one and thats why i didnt make a specific recommendation, because it very much depends on the dac and target output bandwidth you are chasing. but afaik it doesnt just need to be able to cope with the audible music bandwidth, but also to be able to eat up any HF out of band signal and feed it back through the LPF in the loop instead of not coping with the BW and sometimes causing aberrations in the signal. speed for speed's sake is just as silly as RS mentions and having to overcompensate a high speed opamp just to keep it stable in the audio bandwidth or at unity gain as called for in most IV stages; is not what i call a solution.

agreed datasheets are a very good place to start and sometimes a good place to end, particularly if you have no way to quantify the results of other experiments. even if you dont use it in its entirety the information in a good app note is invaluable, but i disagree they are the end game for all dacs by all manufacturers, as there is some truth to the statement that sometimes they are shooting for highest measured performance in a few somewhat dubiously relevant areas. all imo of course

edit, just saw RS's list of mentors

Last edited by qusp; 22nd December 2011 at 04:58 PM.
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Old 22nd December 2011, 08:07 PM   #1616
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@Alexium, I would suggest digging up some of the application notes, tech papers, etc. by some of the better chip companies. You'll find quite a bit at Cirrus, TI/Burr Brown, Analog Devices, etc. In some cases the user guides for their reference boards can be very informative as they often include measurements, design trade off explanations, etc. Sure there's some bias but there's also a lot of good practical objective info.

I would also suggest Benchmark Media. John Siau and a few others have published several white papers on various aspects of DAC performance. Again, not without some bias, but much of it is purely objective and easily verified by others. Anedio has somewhat more biased, but still useful, measurements and info published as well.

The above companies all have measurement equipment, resources, and usually engineering knowledge, that goes far beyond 99.99% of what DIYers have at their disposal. So the pros are in a much more valid and credible position to research what works best and document the results.

@qusp I partly agree about reference designs not always being the "end game" but for somewhat different reasons. I think the biggest constraint on the DAC reference designs isn't so much focusing on the wrong things, but because they're typically somewhat cost and complexity constrained. Being realistic, so are most DIY designs so that's often not a bad thing.

A semiconductor company doesn't want their DAC reference board to cost $1000 to build in low volumes. Nor do they want to imply you need $980 worth of other parts to make their $20 chip perform well. But, IMHO, they aim well past the point of diminishing returns while keeping the component costs and complexity reasonable. You might be able to get another few percent of ultimate performance out of the chip by spending a lot more money, and/or using a substantially more complex approach, but I'd be really amazed if any such changes could survive a blind listening test.

The other area they may somewhat compromise is "nepotism"--they like to specify their own company's parts for obvious reasons even if they're not always the ideal choice. But, again, I doubt that significantly holds back many reference designs.
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Old 23rd December 2011, 08:44 AM   #1617
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Just tried to build my O2 last night.

I'm having some problems with the voltage regulators though. I think they may be cooked but would like another opinion before I go buying more just incase I'm wrong.

AC adapter output is 14.5VAC.

Input to voltage regulators is 16.9V and -16.9V for +/- reg respectively.

From output of the voltage regulators though I'm getting -6.9V and 7V. Polarity same but 5V lower than the expected +/- 12V. This is measured at D1/D5 as per RS testing instructions. Is it likely that I have blown both regulators and each failed regulator is giving an output that is still this well matched?

My camera batteries are flat, I can take a pic once they're charged if it'll help ...
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Old 23rd December 2011, 08:58 AM   #1618
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Doubtful that the regs are cooked. I'd take a real good look for any solder bridges at both top and bottom of the board. Also double and triple check that the power supply components are correct values and installed correctly. I've only skimmed RS's new O2 troubleshooting section of his blog, but so far he's been nothing if not thorough in his documentation. It's likely you'll find help there, aside from anything he may want to add here in the thread.
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Old 23rd December 2011, 10:02 AM   #1619
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Thanks, that is hopefully good news!

Would anyone mind having a gander at these pics, I haven't spotted anything jumping off the page at me yet.

In addition to the measurements in my last post nothing is getting hot/warm which was another of the checks that RS recommended checking for in his testing guide. Power button is still in the off position.
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Old 23rd December 2011, 10:07 AM   #1620
Turbon is offline Turbon  Sweden
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Yepp, you have the regulators in the wrong places. Switch places on them and it will work.

Brgds
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