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Old 13th February 2013, 02:50 AM   #31
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Quote:
Originally Posted by abraxalito View Post
Henry Ott is great but he's not someone (as far as I know) who has listened to high quality digital audio circuit layouts. For those who think I'm just blowing smoke here, try the experiment for yourselves and report back what you hear. I've done that so I know what the result is
Not saying that it will be *bad* to connect it how you're saying, it may well be very good, are you able to say that it is categorically the *ultimate* method of connecting the system? Which is why we're having this conversation I suppose.

He has presented at AES conferences a few times, so I take it that he is at least familiar with whatever special nuances audio electronics design needs over other branches of electronics demanding low noise.

Here is an article about one of those occasions - link.

A quote from that articles:

Quote:
Henry is one of the few consultants that understand system-level design problems. While the semiconductor companies are telling you to cut ground planes up into analog and digital, Henry explains why you are better off keeping a continuous ground plane and how you should use placement and routing discipline to keep noise out of your precious analog circuits. In addition to getting a great notebook of the presentation, you will get a copy of Henrys latest edition of his great book Electromagnetic Compatibility Engineering.
I have only just last week received my copy of Ott's book but when I get some time I will be reading the sections about this topic with interest.


Chris
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Old 13th February 2013, 02:59 AM   #32
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Originally Posted by hochopeper View Post
Not saying that it will be *bad* to connect it how you're saying, it may well be very good, are you able to say that it is categorically the *ultimate* method of connecting the system?
No, I'm not going to claim that, it would be way too arrogant, even for me I'm just putting it out as a suggestion for improvement on what's currently being used. It doesn't cost any more to get the layout better so its a win-win all round as far as I can see.

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He has presented at AES conferences a few times, so I take it that he is at least familiar with whatever special nuances audio electronics design needs over other branches of electronics demanding low noise.
Well when I see him talking about not just digital ground vs analog ground but also signal ground vs power ground then I'll know he's up to speed. AES doesn't have a particularly good history of being concerned about SQ in electronics, though they're better in respect of acoustics. They have published a few good papers though, I recall one by Paul Frindle (an ex-colleague of mine) being excellent though this is going back over a decade and probably was only a convention paper, not in their journal.

It is interesting that he disagrees with the semiconductor companies' recommendations. counter_culture, are you reading this?
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Old 21st February 2013, 02:59 PM   #33
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Hi,

I've added some updates to this build on my blog :

AK4399 | myl8test
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Old 21st February 2013, 03:20 PM   #34
marce is offline marce  United Kingdom
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When doing analogue instrumentation a ground plane is best for numerous reasons. The star refers to a star point where you join power grounds to low level grounds, this has morphed into the horrible spider leg routing that some use today, not the best solution. And for digital layouts a ground plane is a must.
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Old 21st February 2013, 03:24 PM   #35
marce is offline marce  United Kingdom
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Well when I see him talking about not just digital ground vs analog ground but also signal ground vs power ground then I'll know he's up to speed. AES doesn't have a particularly good history of being concerned about SQ in electronics, though they're better in respect of acoustics. They have published a few good papers though, I recall one by Paul Frindle (an ex-colleague of mine) being excellent though this is going back over a decade and probably was only a convention paper, not in their journal.

It is interesting that he disagrees with the semiconductor companies' recommendations. counter_culture, are you reading this
What semi coonductor companies does he disagree with. As to the rest, your probably the only person on this site who has disagreed with what he says!
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Old 21st February 2013, 03:33 PM   #36
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Star gnd for this ? It's not easy to do a star ground for this design - only one ground plane with shared analogue ( 5V and +/-15V ) and digital ( also 5V ). I'm thinking about creating a dual 5V supply with a shared gnd - so two 5V supplies share the same gnd. This is the closest I can get ?

I have put the 1000pF across the 560R - so they have the same gnd point.

Actually, I might change the output stage and go for LME49713HA CFB because they can drive high imp cans directly.

Last edited by KlipschKid; 21st February 2013 at 03:35 PM.
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Old 21st February 2013, 03:43 PM   #37
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What semi coonductor companies does he disagree with.
Its not reported but it will be ones that manufacture ADCs and advise separating ground planes I surmise, so potentially TI, ADI and perhaps Cirrus.

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As to the rest, your probably the only person on this site who has disagreed with what he says!
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Old 21st February 2013, 08:57 PM   #38
marce is offline marce  United Kingdom
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Actually they often recomend one ground plane, though some earlier notes do reccomend seperat ones, as voltages have dropped they often go for one ground. I have numerous papers by Ti National and others I'll dig out some links, there interesting reading, especially in the Ti analogue news letter.
I'll rephrase that out of all the engineers and technical people I have ever met...
I know you have your own whacky views
For the older stuff that worked on decent voltages the high impedance that having a star point creates wasn't a problem, but as I said lower voltages mean that anything that causes one ground to change potential over another can cause problems
KlipschKid, the digital realy does require a ground plane, and for complex digital boards you may have several ground planes to provide return paths for several signal layers, plus power plane pairs (VCC's and GND).
Its an emotive subject is grounding and even in the same R&D lab you'll often get engineers with oposing views! which can make life fun. I treat every layout as a seperate entity, as I do mainly (well almost exclusivly) multi layer and often with SMPS's I use various techniques to keep noise isolated, and minimise current loops and thus limit noise from one section to another. One of the biggest causes of noise is not SMPS's but actual gates switching when you have FPGA's MCU DDR etc, the instantaneous current requirements are often in the 100A range and there is very little you can do to stop that kind of load causing ground bounce.
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Old 21st February 2013, 09:20 PM   #39
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Originally Posted by abraxalito View Post
Henry Ott is great but he's not someone (as far as I know) who has listened to high quality digital audio circuit layouts. For those who think I'm just blowing smoke here, try the experiment for yourselves and report back what you hear. I've done that so I know what the result is
Why is your high frequency return current flowing in the analog portion of your ground plane? It only wants to return via the lowest impedance (inductance) path which is going to be right under the trace. So if you do have a HF problem, your layout is not optimal.

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.

I would say your assertion that good design for EMC and instrumentation is different than for audio is a dubious one.
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Old 21st February 2013, 10:16 PM   #40
marce is offline marce  United Kingdom
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I agree on the low frequency currents, as they get nearer DC they want to follow the path of least resistance, and one reason why system ground loops can be a problem. The problem with audio it covers a range of frequencies that cover the crossover from path of least resistance to least inductance (at 20kHz the current density is not as steep as under a 1MHz+ signal); low frequecies can find the path of least resistance is often the protective earth loops. Providing the lowest impedance and resistive 0V return path helps.
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