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Old 11th January 2004, 10:18 PM   #1
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Question grounds in TDA1543 based dac

Dear all!

Is there any sonic difference if you group
analogue grounds to analogue and digital
grounds to digital or if You connect them
together in one ground (o.k. I know that they
are (at the end) all connected together but
is there any sonic benefit of grouping grounds and then
connecting them together beside that You avoide
hum that way and that sort of things).
Could anyone explaine this to me please?

p.s. I have made my prototip dac around one ground
and have no problems with hum or anythinf unusual.
So I am wondering am I missing something in
sound of it.......
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Old 12th January 2004, 08:15 PM   #2
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anybody
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Old 13th January 2004, 02:34 PM   #3
ZERS is offline ZERS  France
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Hi,

The digital grounds and analogs one are qite different and the noise isn't the same.

Pratically, both must be shared on PCBs and the connexions between us must be done through a 100k (or more) resistor.

The "signal" within each of grounds has not the same nature and it's clear that the noise in the analog ground disturbs the digital part.

In terms of sounds, the sounds looks less clear.

Hope is help
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Old 13th January 2004, 07:43 PM   #4
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We'll try it and let You now- when I take a look on my pcb I have my grounds separated but connected with one tiny path with each other. I will cut that path and try with 100k in there to connect them
thanks
daniel
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Old 13th January 2004, 08:58 PM   #5
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Dear ZERS

I have separated all my digital grounds from analogue ones with 100k as U suggested. I could hear, in my speakers, that my dac was oscilating .
Turned down to 10k - oscilations were less to hear. Disconected the resistor- no oscilations. I will leave it separated with no resistor only connected with a tiny wire.
Best regards
daniel
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Old 13th January 2004, 10:39 PM   #6
ZERS is offline ZERS  France
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this is quite surprising. It must depe,d on the way the PCB is built.

Ispričavam se!
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Old 15th January 2004, 11:02 AM   #7
guido is offline guido  Netherlands
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General rule for DAC/ADC grounds:

Connect analog and digital gndplanes at the DAC/ADC, if not possible (more than one DAC, other reasons):

Connect analog and digital gnd pins to ANALOG ground.

Connect analog and digital together at the DAC/ADC as short track as possible. Any restistance between analog/digital would generate a voltage difference between analog and digital gnd pin.

Any voltage between those pins is then also present on the output!

Got this from an analog devices application note, together with the technical background. Not shure this applies for all DAC's/ADC's, check the datasheet.

E.g. this is stated in the BB PCM63, page eight

http://focus.ti.com/lit/ds/symlink/pcm63.pdf

So NOT the way elektuur did it in their first DAC.....

GuidoB
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Old 15th January 2004, 07:54 PM   #8
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Thanks- I was a little suspicious about that 100k resistor as ZERS and I have comented via mail but what a heck I give it a try to see what happens. It was not very nice to hear- as expected.....
daniel
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