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PO89ZB , an inline DC filter for SMPS wall warts . Preamps, HPA, Korg NuTube, etc
PO89ZB , an inline DC filter for SMPS wall warts . Preamps, HPA, Korg NuTube, etc
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Old 23rd May 2021, 11:19 PM   #681
ranshdow is offline ranshdow  United States
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Quote:
Originally Posted by rikiheck View Post
Bummer. I've heard that same sound and was hoping this might help. Maybe I'll get lucky, though.

If you solve it, please let me know!
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Old 24th May 2021, 08:24 AM   #682
jaaptina is offline jaaptina
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Quote:
Originally Posted by ranshdow View Post
If you solve it, please let me know!
Hans Beekhuyzen has some very comprehensible videos on high end pi streamers. Sure he has the hiss solved.
HifiBerry DAC2 HD sound card for Raspberry Pi - YouTube
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Old 25th May 2021, 05:23 AM   #683
syklab is offline syklab  Hong Kong
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Just read this from Digikey with good explanation on TVS.

Blocked
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Old 27th May 2021, 08:12 PM   #684
wealas is offline wealas
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Quote:
Originally Posted by ranshdow View Post
If you solve it, please let me know!
First try wired network (make sure WiFi is disabled), then try to separate the DAC from the RPI with a ribbon cable and some metal between the two.
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Old 28th May 2021, 06:50 PM   #685
strongbow60 is offline strongbow60  Sweden
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I ordered a cheap LLC switch mode power supply from Ali Express. Now doing that is a lottery, sometimes you are surprised.
This PS is intended as a built in for an ACA so it is single voltage and 24 V.
To use the filter in an ACA I will use slightly different values for some of the components, more on that later. Also a thicker copper layer on the PCB. And one filter per channel.

24V LLC power supply.png

I tested it yesterday on the bench to see what I got. The voltage is stable to the second decimal between a light load and 1 A continuous, that is expected. But the noise... is interesting, 3 V peak to peak, horrible!

SDS00001.png SDS00002.png

Putting a well known filter between the PS and the load made a difference, now it is 600mV of high frequency noise, at one ms interval....

SDS00003.png SDS00004.png

I will see if it is possible to tune the filter to better suppress the high frequency content, but that will be a trial and error proposition for me.

Last edited by strongbow60; 28th May 2021 at 06:52 PM. Reason: wording
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Old 28th May 2021, 07:30 PM   #686
Kartapus is offline Kartapus  France
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Price please because standard in the switching PSU industry is to have 1% of ripple so 240mV max for +24V output. Most of known manufacturers do that. Some of them are better (<100mV of ripple).

Manufacturers like Meanwell, TDK Lambda, XP POWER have very good PSU for a good price (for me).

Another remark, noise and ripple are not the same thing. Ripple is at switching frequency (value is on the datasheet). Noise is more difficult to know by technical documentation and only an oscilloscope can sometime give the information but it needs an oscilloscope with a high bandwidth (forget 20MHz, at least 100Mhz and maybe 500MHz in some cases).

So best way for filtering is tgo design a filter for each "problem". One calculated for ripple (f ~100kH-500kHz, see datasheet for swithing frequency) and another one for noise (f > 10~50~100MHz, small capacitors value + self with a high sfr value to "go" in the very high frequency).
Attached Images
File Type: jpg illustration.jpg (66.1 KB, 315 views)

Last edited by Kartapus; 28th May 2021 at 07:35 PM.
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Old 29th May 2021, 05:37 AM   #687
strongbow60 is offline strongbow60  Sweden
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Join Date: Jul 2017
Good points.
Yes there are better alternatives, but I see a lot of people buying there supplies, and this is after all DIY. I like to see how far I can take it and not ruining the regulation.
Low frequency ripple is resonable, I think. The high frequency not so and there is where the high peaks are. This might not be a problem in my application, but I like to tinker.
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Old 29th May 2021, 08:42 AM   #688
Kartapus is offline Kartapus  France
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The final choice is ears

And of course, it depends on application because for an amp, ripple & noise are less important than for a preamp.
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Old 29th May 2021, 10:36 AM   #689
Mark Johnson is offline Mark Johnson  United States
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PO89ZB , an inline DC filter for SMPS wall warts . Preamps, HPA, Korg NuTube, etc
The scope picture below is explained in post #515 of this thread. Click on the image to see it full size and undistorted.

Click the image to open in full size.
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Old 30th May 2021, 04:13 PM   #690
ggetzoff is offline ggetzoff  United States
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Hi Mark,

Thanks as usual for all your hard work. Is a Rev. B. coming? The reason I ask is the store is out of the boards and was just wondering if they are coming back.

Cheers,

Greg
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