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Old 27th April 2003, 02:53 PM   #1
nFORCE is offline nFORCE  Japan
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Angry DSP and DAC noise

Dear all,

Some question need you help.

I DIY the YAMAHA DSP (YSS932) and DAC is CS4360.

The problem is some noise heard in the output. Like a pink noise.

When I seperate the DAC to another board, it reduce a much.(near to ZERO)

The current length of the DSP to DAC about 3CM.

I read more DAC application note and found most of the DAC are placed to DSP/Digital Receiver atleast 10CM.

Is it the root cause?
Or is it interference by the "Ground Bounce"

When I remove the MCK of DAC, (short the MCK pin of DAC to GND), there are no any noise heard in output, i.e, my Analog layout is OK.

Please help me and comment

Thank alot
Regards,
nFORCE
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Old 27th April 2003, 04:24 PM   #2
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Lightbulb Re: DSP and DAC noise

Quote:
Originally posted by nFORCE
Dear all,

Some question need you help.

I DIY the YAMAHA DSP (YSS932) and DAC is CS4360.

The problem is some noise heard in the output. Like a pink noise.

When I seperate the DAC to another board, it reduce a much.(near to ZERO)

The current length of the DSP to DAC about 3CM.

I read more DAC application note and found most of the DAC are placed to DSP/Digital Receiver atleast 10CM.

Is it the root cause?
Or is it interference by the "Ground Bounce"

When I remove the MCK of DAC, (short the MCK pin of DAC to GND), there are no any noise heard in output, i.e, my Analog layout is OK.

Please help me and comment

Thank alot
Regards,
nFORCE
Hi nForce,
Delta-Sigma DAC's produce a lot of out of audioband noise. Elegantly called noise-shaping. This can fold back into the audioband causing audible noise. Do you have adequate analog lowpass filtering after the DAC? I once measured 1.5V AC with a analog voltage meter after a Crystal DAC without lowpass filtering.


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Old 27th April 2003, 06:23 PM   #3
nFORCE is offline nFORCE  Japan
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Dear Elso,

I take a measure with original Yamaha demoboard.
It is using AKM 4527B.
It is not need additional LPF.

For my design, I use Crystal CS4360 with additional LPF.

I use the design tools from TI and the noise figure (using CROto monitor) is little than before. 20 times smaller than previous.

Now, I can see a lot of noise in CRO and can heard.
The noise level is 10mV-15mV. (like a FM noise sound)

I take a measure in Yamaha demoboard, the CRO can display the noise (same level of my one) but cannot heard that noise.

Please comment.

Thanks
nFORCE.
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Old 27th April 2003, 06:56 PM   #4
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Question Noise

Hi nForce, Maybe a grounding issue?
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Old 29th April 2003, 03:18 PM   #5
A 8 is offline A 8  Sweden
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nFORCE,
Don't know if this will give you any ideas....but I just tweaked an old pioneer cdp with one bit dacs.
I changed the clock and built a digital out reclocking curcuit.
By accident (the plan was just to use it as a transport) I checked analog out after the mod and found it to have the exact artifact you described. Sounds like FM noise probably -30 to 40dB below signal max.

The way I implemented the clock I skipped one clock gate before reaching the dacs and when I add it again the noise is gone.

So...perhaps you have a timing issue between the dsp and dac and/or that your combination of jitter level and tolerances gives you this problem
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