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Old 22nd February 2013, 12:56 AM   #41
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Jim Brown (who is very much into audio) writes about Henry W. Ott:

The author, and our entire industry, are greatly indebted to Henry Ott, whose excellent workshop on EMC I attended in 2004, and whose book, cited above, should be on everyone’s shelf. It would be difficult to conceive of an issue related to EMC that Henry hasn’t thought through in great detail, considering every possible ramification, from the micro to the macro, and from circuit performance to manufacturability to user-friendliness to where things will be in 20 years. A side-comment in his book (first published in 1976, updated in 1988 and again in 2009) makes it clear that he knew about
SCIN at least 20 years ago.
&
An absolutely essential book. Henry Ott nailed it,in this definitive text that ties together both theory and practice in EMC.
If you disagree with a single word in this book, you’re wrong!
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Old 22nd February 2013, 01:02 AM   #42
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lol, love the last line yeah even the free stuff on his site is superb
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Old 22nd February 2013, 01:38 AM   #43
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Default Headphone output ?

Hi,

I have a question about changing the EVM circuit to use a current feedback op amp, the LME49713HA. It has +/-100mA output and can "easily drive 150R loads" and it seems to have pretty low distortion and noise too, and is able to drive some capacitance. So I think it should be able to drive headphones like Senn HD650 directly, if I add some gain.

I am planning to remove C1 and add a 600z ferrite in series after R1, or I could keep C1 and cut the trace into the neg op amp input and put the ferrite there. This follows Ti's advice about using cfb op amps, that Abrax posted in the es9018 thread. So, without having sim software, which one seems like the best idea ? What about C2 ? I assume it can stay since it is not in the neg f'back loop so it won't cause instability.

Then I need to change the resistor values for some gain, say +3, so change R2 and R3.

I was also thinking of reducing R5 to see if it would improve dynamics. Did I understand this right ?
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Old 22nd February 2013, 03:16 AM   #44
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http://www.ti.com/lit/an/slyt099/slyt099.pdf
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Old 22nd February 2013, 03:23 AM   #45
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Quote:
Originally Posted by chris719 View Post
Why is your high frequency return current flowing in the analog portion of your ground plane?
You got me, I wasn't aware that it was - after all I don't have a groundplane, rather I use star earthing.

Quote:
It only wants to return via the lowest impedance (inductance) path which is going to be right under the trace.
Yep, I agree. This is EMC101.

Quote:
So if you do have a HF problem, your layout is not optimal.
I agree - do you think I have a problem then?

Quote:
A single ground plane does not work very well if you have a lot of large, low frequency return currents though, since it may be harder to predict the path they will take and their "spread" through the plane will be greater.
This tends to be what happens in digital systems - the common-mode currents meander through the plane in ways that the designer hasn't thought about. I could point to any number of examples - one that comes to mind is the Metrum Octave which I think I commented on in a thread last year. The guys who know how to do this right at those at Berkeley Audio Design. Take a look at the Alpha DAC's internal PCB.

Quote:
I would say your assertion that good design for EMC and instrumentation is different than for audio is a dubious one.
Well the requirements are different - in instrumentation the aim isn't to please the ears. But I'm more than willing to be shown wrong - it would result in even better SQ.

@marce - its not really that my views are whacky, rather that my practices are. I just report here what I do, what works for me.
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Last edited by abraxalito; 22nd February 2013 at 03:27 AM.
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Old 22nd February 2013, 04:11 AM   #46
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I'm asking questions I know the answers to, in the hope that someone will decide that answering the questions is more productive than debating who's got the biggest handbook.

But hey, why not hijack the thread and add loads of noise ?
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Old 22nd February 2013, 12:18 PM   #47
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I cannot get this DAC to play music.

I have checked all power points, signal connections, data connections, etc. There are no shorts and all connections are good, with all the right pins getting the voltages, gnd, signal, etc they need. I can get it to buzz, hum, crackle, pop, etc but not decode pcm.

I have all the dif0-2 high for 32 bit I2S (which is my source, tested on other DACs too) and I have tried tying dif2 low for 24 bit i2s. I have also tried tying dem1 low to set de-emphasis to off, just in case.

There is no dc offset or any ACV on the output either.

It seems to me that it is not an analgoue problem because I an get continuous noise/hum by putting a finger on the wire near the dac output. The op amaps and circuitry are working.

With the op amps on, if I turn off the DACs power and then on again, I can get a thump.

So, I think it must be the i2s. I checked the board has been labelled correctly, and i checked and re-checked my source and the connecting cable.

There doesn't seem to be anything left to check, so that's why I'm posting this. My first failure.
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Old 22nd February 2013, 12:19 PM   #48
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Quote:
Originally Posted by KlipschKid View Post
Wah, very cool - great skills ! What size are they ? Only those four pins ? Any tips for me about building this ? Thanks.

and Kung Hei Fat Choi !
1) zero distance decouple cap is a must, without it, my ear will complain in 5 minutes.
2) use solder to fill all via
3) direct solder the opamp to the PCB,
4) use fet/jfet input opamp/ opa627/ad8610br etc.
Diyer can try one by one and should find the sound is improving more and more
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Old 22nd February 2013, 12:32 PM   #49
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Quote:
Originally Posted by KlipschKid View Post
I cannot get this DAC to play music.

I have checked all power points, signal connections, data connections, etc. There are no shorts and all connections are good, with all the right pins getting the voltages, gnd, signal, etc they need. I can get it to buzz, hum, crackle, pop, etc but not decode pcm.

I have all the dif0-2 high for 32 bit I2S (which is my source, tested on other DACs too) and I have tried tying dif2 low for 24 bit i2s. I have also tried tying dem1 low to set de-emphasis to off, just in case.

There is no dc offset or any ACV on the output either.

It seems to me that it is not an analgoue problem because I an get continuous noise/hum by putting a finger on the wire near the dac output. The op amaps and circuitry are working.

With the op amps on, if I turn off the DACs power and then on again, I can get a thump.

So, I think it must be the i2s. I checked the board has been labelled correctly, and i checked and re-checked my source and the connecting cable.

There doesn't seem to be anything left to check, so that's why I'm posting this. My first failure.
1) check the 10uf and 20k near the reset, and 20k near the mute is all soldered ok.
2) try to short the reset after power on, if it sound, your 10uf and 20k near the reset should have problem.
3) check the fb is soldered
4) no need to install the switch SW1 if connected from our cm6631/a pcb, just make sure all 20k is soldered
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Old 22nd February 2013, 01:41 PM   #50
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1) all good - 5V accross 10uF cap
2) no sound/pop/etc, actually cuts noise when noise is present - Noise is sometimes present when the i2s gnd is disconnected, and very rarely there is distorted music hidden very quiet under the noise.
3) already checked and re-checked
4) had to try - tried everything.

The i2s sources are cm6631 and wolfson wm8805. both the same problem.

What voltage should there be on vcml and vcmr ? I have 0V. All power supply pins are correct.

cheers

Last edited by KlipschKid; 22nd February 2013 at 01:51 PM.
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