[SOLVED] PT8211 Audio DAC channels "bleeding/spilling" into each other ?

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nicolas_soundforce
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[SOLVED] PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by nicolas_soundforce » Fri Sep 29, 2017 10:47 am

Hi guys,

Anybody experience the same problem ? I got it to work and playing audio files from a sd card, sounds great. But I am experiencing a lot of "bleeding" from one channel to the other. I mean for instance, I can hear the left channel in the right channel, when the right channel is "silent". I am using op-amps to amplifing the signal for my usage. Could that be related to the analog circuit or is the PT8211 just "that bad" ?

See my schematic, I am listening to OUT1 and OUT2:

Image

ag123
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by ag123 » Fri Sep 29, 2017 2:42 pm

the schematics looks pretty good but sometimes one could check the board if there are some 'accidental' capacitive coupling or even literal shorts
i posted something about vbat here, and i think due to my poor soldering skills there might literally be a short somewhere
viewtopic.php?f=3&t=2602
i bought a usb microscope to examine it closely
https://www.ebay.com/sch/i.html?_nkw=us ... e&_sacat=0
and i noted that there could be literally microscopic filaments clustered around contacts which i do not know if they are after all conductive

stevestrong
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by stevestrong » Fri Sep 29, 2017 3:39 pm

Filter better the power supply of TL074P.

nicolas_soundforce
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by nicolas_soundforce » Fri Sep 29, 2017 3:45 pm

stevestrong wrote:
Fri Sep 29, 2017 3:39 pm
Filter better the power supply of TL074P.
Interesting, for example with an extra 1uF on V+ and V- ?

At the moment I have 0.1uF between +12V/GND and 0.1uF between -12V/GND.

nicolas_soundforce
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by nicolas_soundforce » Fri Sep 29, 2017 5:26 pm

I found something intersting I believe : http://www.ti.com/lit/an/slyt190/slyt190.pdf

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Pito
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by Pito » Fri Sep 29, 2017 6:32 pm

Audio frequencies require hundreds of uFarads for decoupling. Let the 100nF there, 100nF filters out hundreds of kilohertz to few mega.
Rule of thumb:

Code: Select all

Capacitor               Effective for decoupling
=============================================
10000uF                 till ~100Hz
1000uf                  till ~kHz
100uF                   till ~100Khz  (low esr)
10u ceramic/tant smd    till ~1MHz
1u  ceramic smd         till ~few MHz
100n ceramic smd        <10MHz
10n  ceramic smd        ~100MHz
1n   ceramic smd         <1GHz
100p ceramic smd        ~GHz  (special shaped)
1-10pF ceramic smd      <10GHz (special shaped)
If you want to cover ~100Hz .. ~few MHz you have to wire the capacitors in parallel, ie 1000uF||10uF||100nF..
If you want to cover ~few MHz .. ~1GHz you have to wire the capacitors in parallel, ie 1uF||10nF||100pF..
The smaller value capacitor always closer to the pin you want to decouple.
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nicolas_soundforce
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by nicolas_soundforce » Fri Sep 29, 2017 9:32 pm

Thank you Pito.

The problem is definitely the op-amps/analog circuits. I added extra 10uF caps which make a slight difference. I also tried a second PT8211 with another WS pin and send the other channel only to that one, it made no difference.

I think using a quad package op-amp was a very bad idea. I will experiment with 2 x TL072 and see if the spillage gets reduced.

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Pito
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by Pito » Sat Sep 30, 2017 11:22 am

Except using 1 opamp (low noise type) per package and the combined decoupling as above, the grounding - ie. separating the analog gnd and digital gnd is vital in such circuits.
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nicolas_soundforce
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Re: PT8211 Audio DAC channels "bleeding/spilling" into each other ?

Post by nicolas_soundforce » Sun Oct 01, 2017 4:44 pm

We were right! Using a quad package op amp was a mistake. I switched to 2 x TL072 and the spilling was completely gone.
Silly me, lesson learnt!

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