Static Noise over the track sound

Designing hardware that uses VLSI Solution's devices as slave codecs such as an external MP3 decoder chip for a host microcontroller.
Jeremyvnc
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Static Noise over the track sound

Post by Jeremyvnc » Fri 2011-10-28 6:59

So, I ordered my first set of boards and didn't have any performance issues with them once I got the code sorted out. Then, I ordered a second set of boards using a different sd card slot and changed some capacitors from 0603 to 1206 and have been having a sound issue. Board layout is the exact same as the prior design because the new card slot fits without modification (the previous boards I had ordered 0603 capacitors by accident).

I have tried everything I know of to get these new boards to get rid of the static noise. I tried checking and ohming all of the components for good solder points, I checked for bridges between traces, unsoldered the sd slot and put on the original and I even reloaded my code on both an old board and new board. The old board sounds great while the new board plays the file but with static.

The last thing I can think of is that my output filter isn't good enough. Could you mind looking at my filter and interface to the VS1053?

Thanks,
Jeremy
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pasi
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Re: Static Noise over the track sound

Post by pasi » Fri 2011-10-28 8:47

Hi, where's your RCAP capacitor?
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Jeremyvnc
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Re: Static Noise over the track sound

Post by Jeremyvnc » Fri 2011-10-28 15:30

I guess I don't have one. What does RCAP do? I thought it was only used for line in and mic.

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pasi
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Re: Static Noise over the track sound

Post by pasi » Fri 2011-10-28 20:17

Jeremyvnc wrote:What does RCAP do?
RCAP is (with the capacitor) the filtered reference voltage for the analog. It is one of the most important things to get right. Check the layout guidelines for the capacitor, although vs1053 is not quite as sensitive to the grounding of RCAP capacitor.

Larger capacitor filters better, but it takes longer to charge, so it takes longer to be able to use full swing.

If you connect to external amplifier instead of headphones, also check how to add a low-pass filter to the outputs (to prevent the 6MHz DAC noise possibly aliasing in the amplifier). See viewtopic.php?f=9&t=69.
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Jeremyvnc
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Re: Static Noise over the track sound

Post by Jeremyvnc » Fri 2011-10-28 20:31

For my testing here, I'm connecting it directly to headphones but in normal operation, I connect it to an amplifier.

Would the RCAP be whats causing the static?

Also, my filter caps are 1206 ceramic, should they be a polarized capacitor? I notice on the MDFly break out boards and the board shown here that they use polarized capacitors for the output filters. I'm no pro at this and would really like to understand where the static is coming from. I'm no expert when it comes to analog circuits.

I'll try a 1uF cap on the RCAP pin and see what that does for me.
Last edited by Jeremyvnc on Sat 2011-10-29 0:32, edited 1 time in total.

Jeremyvnc
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Re: Static Noise over the track sound

Post by Jeremyvnc » Sat 2011-10-29 0:32

No change with the RCAP set at 1uF. I soldered a 40 gauge wire to the RCAP (pin 44) to the capacitor (ceramic 1206) then a 24 gauge wire from the cap to AGND.

Also, I'm going to try to rebuild the output filters like in the diagram you linked to. I don't have some of the smaller capacitors and the local store here doesn't have the exact values either. Can you confirm for me if I can replace the 3.3nF with 4.7nf (0.0047uF ceramic).

So as I can tell, there is 3 stages of filtering: High Freq Grounding Path, Sigma-Delta reconstruction, and DC block for output.

In my circuit, I used an RC circuit for DC blocking but put it in series with the output lines. Could this be my problem?

Is there anything else I should be aware of or have done wrong with my circuit? One issue I had with the first circuit is that I could only use certain SD cards. Any ideas why that would be?

Thanks for all the help thus far!

Jeremyvnc
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Re: Static Noise over the track sound

Post by Jeremyvnc » Sat 2011-10-29 5:09

Okay, I unsoldered resistors R12,R13,R14,R15 and soldered wires to the output of the LEFT and RIGHT channels and two wires to the headphone/line-out connector and connected those to my breadboard with the following circuit. Still no change in the output. The static remains. Please help me with this situation. I want/need to order additional boards if I can't fix these but I'm confused if the old boards work and these do not.

Again, thanks for any and all help you can have give me.

-Jeremy
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Panu
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Re: Static Noise over the track sound

Post by Panu » Tue 2011-11-01 14:10

Jeremyvnc wrote:One issue I had with the first circuit is that I could only use certain SD cards. Any ideas why that would be?
This would point to potential problems (noise, wrong/too low voltage level) in the digital VDD to the SD card. Also bad ground connection of the SD card can cause this.

-Panu
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Panu
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Re: Static Noise over the track sound

Post by Panu » Tue 2011-11-01 14:21

Hi!

Hmm... taking a second look at the schematic, where does the SD card take its power? It should take it directly from the 3.3V power supply or have a PMOS transistor in series if you want to switch it off. Now it just says "A2".

-Panu
Info: Line In and Line Out, VS1000 User interface, Overlay howto, Latest VSIDE, MCU Howto, Youtube
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Jeremyvnc
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Re: Static Noise over the track sound

Post by Jeremyvnc » Tue 2011-11-01 18:26

I think I need to transistor because A2 is an output on my microcontroller.

I'm still flabbergasted as to where the static is coming from.

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