I discovered CDP ground plane. What should I do with it? - diyAudio
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Old 24th November 2004, 10:36 PM   #1
DIAR is offline DIAR  Finland
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Default I discovered CDP ground plane. What should I do with it?

I have read a thousand times about how important CD player ground plane issue is. I still haven't quite understood what I should do with it.

I coloured the ground plane of my Sony DVP NS900 analog output PCB (brown):
http://kotiweb.kotiportti.fi/audiovi...ge_1_vari1.gif

Here are the schematics of analog output PCB:
http://kotiweb.kotiportti.fi/audiovi...og_output1.png
http://kotiweb.kotiportti.fi/audiovi...og_output2.png

Should I separate the ground planes (cut some jumpers) of each OPA amps and connect them to power input on the right (CN301 connector pin 3, area B10) with separate wires (star ground).

I'm worried about is the 5 V regulator (IC351 B1-2) that is feeding the DAC chips .The ground trace is a mess and the regulator is located about 15-20 cm from the DAC chips which are on another pcb. The ground plane of the DAC pcb is connected to analog output pcb through CN101 connector (area D4).

I was thinking that it might be wise to cut the ground and voltage supply traces from analog output pcb to DAC pcb and place the regulator closer to DAC PCB and use a separate wire to connect DAC pcb ground straight to power input on analog output PCB (CN301 connector pin 3, area B10). (I will still have to have a regulator on analog output PCB for feeding the digital output circuits)

Here are some pictures of the pcb's. The small DAC chips are on the bottom side of the SMD pcb. (I've changed some components after taking a few of the photos)

http://kotiweb.kotiportti.fi/audiovi...geo43pg1p5.jpg
http://kotiweb.kotiportti.fi/audiovi...geo53pg1p5.jpg
http://kotiweb.kotiportti.fi/audiovi...g1geo146p5.jpg
http://kotiweb.kotiportti.fi/audiovi...g1geo274p5.jpg
http://kotiweb.kotiportti.fi/audiovi...g1geo167p5.jpg

I'm sorry about the huge pictures. I just want you to see every possible detail. If you need more pictures, please ask.

Thanks for helping me out!!!
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Old 25th November 2004, 08:34 AM   #2
Alien8 is offline Alien8  Belgium
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Correct me if I'm wrong, but your grounds (I wouldn't call them planes) already seem separated. You gave them the same colors, but upon a quick look, I couldn't see them connected at any point...

Also, where are your dac's ?
I would think that THE dac (usually a all in one giant smd thing) is on the DSD board. So from what you're telling the 'digital' supply is located on the analog board and fed through the connector to the DSD board. BTW these dacs are already (symmetrical) voltage out, the opamps are just filters/buffers and to go single ended.

Well at least you don't have a switching psu (for the analog) which is allways good !!

hth

A8
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Old 25th November 2004, 09:05 AM   #3
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Question "Ground Plane"?

Hello DIAR,
That is a typical example of the lay-out of Sony PCBs.
Thy do it all the time even in the most expensive SCD-1. I wouldn't call it a groundplane. Not much to do about it unless you want to design and etch a new PCB. I feel the best you can do is adding liberal decoupling caps at the supply pins of the ICs.
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Old 25th November 2004, 10:19 AM   #4
Alien8 is offline Alien8  Belgium
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I stand corrected, they are connected...
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Old 25th November 2004, 06:04 PM   #5
DIAR is offline DIAR  Finland
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I will replace some of the SMD electrolytic caps with Os-Cons. Some of the SMD caps are very small and impossible to replace with my skills and equipment.

I was thinking that I might get better results if I place a second 5V regulator right next to the DAC chips. Now the distance between regulator and DAC is huge.

I could also cut the ground wiring from the original regulator so that for example digital output circuits (optical and coaxial) can't cause any interference. Now the digital output circuits and DAC are are fed by the same 5 V regulator and I would like to make the power supplies separate. This picture will probably make things more clear:
http://kotiweb.kotiportti.fi/audiovideo/download/ps.jpg

Or should I stick with the original configuration and just change or add some bypass caps?
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Old 26th November 2004, 04:51 AM   #6
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Default "I still haven't quite understood what I should do with it."

Unless you can measure that there is a difference in potential, or that capacitor ripple current is upsetting a regulator's performance, why do you want to do anything with it?

Yes, they are frequently done wrong. The only way to know for sure is to be able to measure it, because only then will you know what to do about it.

If you can't, you are most likely stuck with it.

Jocko
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Old 26th November 2004, 06:26 AM   #7
DIAR is offline DIAR  Finland
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Ok. The regulation stays as it is.

I changed the three SMD electrolytic caps that were marked in the picture in my previous post. I used 100 uF Os-Con caps.

I almost soiled my underwear when removing one of the caps
I heated it with two solderin irons. Apparently I applied too much heat and the cap exploded! There was a big blast and thick brown smoke and the metal can flew about 30 cm high.

I think I'll continue building my Tentlabs XO power supply.

Thanks for help!
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Old 26th November 2004, 09:32 PM   #8
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Usually a good way to connect two grounds between two digital sections, DSP chip and DAC chip for example is via one (or two in parallel) ferrite beads. This technics allows for same DC and low frequency AC potential, but for high frequency AC (RF) it represent very high impedance, depending on ferrite material used preventing influence of two stages on their performance at high frequencies.
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Old 27th November 2004, 01:36 PM   #9
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Quote:
Originally posted by Extreme_Boky
Usually a good way to connect two grounds between two digital sections, DSP chip and DAC chip for example is via one (or two in parallel) ferrite beads. This technics allows for same DC and low frequency AC potential, but for high frequency AC (RF) it represent very high impedance, depending on ferrite material used preventing influence of two stages on their performance at high frequencies.

Hi

This will only work correctly if NO AC currents flow through that bead.

If it is the case however, induced voltage will appear in series with ALL signals crossing that barier - Conclude yourself what impact hat may have. Some may like the sound that is the result of such architecture, I do not:

http://www.tentlabs.com/Info/Article...decoupling.pdf

Bottom line: Keep groundplane closed and make sure no or contolled currents flow through the plane

Instruments are things like series inductors / resistors combined with local (and well connected) decoupling. Other are the deliberate use of shunt regs with high input impedances

http://www.grimmaudio.com/ad1grimm.htm

cheers
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Old 28th November 2004, 11:37 AM   #10
DIAR is offline DIAR  Finland
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Here's a picture of the Oscons that I used to replace the original SMD electrolytic caps. I had to remove the old caps because there wasn't any other good place for the caps. I tried to keep the cap leads as short as possible. Is the lenght of the leads critical?

http://kotiweb.kotiportti.fi/audiovi...ad/osconit.jpg

In the backgound you can see AD8065 OPA amp module (from LC Audio) and OPA627 module. The smaller output caps are Glack Gate HQ NX 47 uF in Super-E-Caps configuration.
The small PCB is an LM317 regulator module:

http://kotiweb.kotiportti.fi/audiovi...geo38pg1p5.jpg
(The resistor values are smaller to maintain a sufficient load at all times)
http://kotiweb.kotiportti.fi/audiovi...geo29pg1p5.jpg

Tomorrow I get MSR860 diodes for power supply.
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