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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 13th December 2020, 02:02 PM   #231
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Mark Johnson View Post
Hi Jan, no I haven't published measurements or LTSPICE files. A couple of builders uploaded before-and-after oscilloscope photos, showing time domain behavior, and it looks quite pleasing. Anecdotally.

A quick calculation of the filter's input impedance might suggest how easy or how difficult it could be, to take physical measurements of its frequency domain behavior.

Thus, lacking rigorous data, this PCB and project is merely a very inexpensive "try it yourself and see what YOU think" little audio board.

If you, or anyone else, wants to create an LTSPICE simulation of PO89ZB, starting from a blank sheet of paper, you'll need to obtain six constants. Either by digging through datasheets, or doing a little EE math, or measuring actual parts, or a combination of the above.
  1. The series resistance of each inductor
  2. The (parasitic) parallel capacitance of each inductor
  3. The inductance of each inductor
  4. The equivalent series resistance of each capacitor ("ESR")
  5. The equivalent series inductance of each capacitor ("ESL")
  6. The capacitance of each capacitor
Several of these are discussed in depth, in the citations presented in post #9 above.

Once you've created a simulation that you trust, you can do some "sensitivity analysis" to discover which of the six constants above, have the greatest effect upon the filter's behavior. Maybe you'll find out that a couple of them have comparatively small effect; varying them by +/- 25% only changes the filter behavior by +/- 3%, for example. Then you can berate and bitterly reproach yourself for working so very hard to get a semi precise estimate of those constants, when in reality a rough guess would have worked equally well. Or maybe you'll find that there are no low-sensitivity constants and hard work has paid off handsomely, every time.


_
Maybe people like Würth have spice models for their inductors. I'll see if I can find something.

Jan
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Old 13th December 2020, 02:08 PM   #232
TNT is offline TNT  Sweden
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PO89ZB , an inline DC filter for SMPS wall warts . Preamps, HPA, Korg NuTube, etc
Quote:
Originally Posted by strongbow60 View Post
TNT: I don't know what the issue is with the specified resistors. Mouser.se has them in stock. The only part I had to buy from another supplier where the inductors which I found in stock at elfa.se. Or use the one Claude found.
No issues. I just wanted to understand if those smd resistors could be a substitute to the one in the BOM. Thats all.

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Last edited by TNT; 13th December 2020 at 02:37 PM.
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Old 13th December 2020, 02:10 PM   #233
strongbow60 is offline strongbow60  Sweden
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About power consumption for Raspberry Pi, dependent on how it is used, the current filter will be sufficient. Most problem with third party power supplies (wall warts) are that they often give slightly below 5V and the Raspberry is sensitive to that.
See this page for current requirements for RPi
Power Supply - Raspberry Pi Documentation
I have tried RPi 2, 3B+ and 4 with one of my filters and only ethernet and/or Wifi connected and they worked reliably, at least for a day or so. I normally use RPi2 for my two music servers and they are up and running all the time with a filter applied.
If USB devices are needed then a powered hub should work.
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Old 13th December 2020, 02:22 PM   #234
joensd is offline joensd  Germany
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The only issue with the resistors is the power dissipation with whatever current you need from your supply.
The resistors from post #1 will have better thermal resistance as SMD resistors lying on a board and you sure donīt want to get near even half their stated power dissipation.

Other than that I wouldnīt go below the value Mark suggests.
These are dampening resistors for the LC also. Pure LC-filter can make SMPS instable and this filter is supposed to be kind of generic and work with "every" SMPS out there.
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Old 13th December 2020, 03:06 PM   #235
Brakspear75 is offline Brakspear75  United Kingdom
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Well in the spirit of experimentation (and making decisions....) I've ordered parts and boards to build 10 of these, using the Nichicon capacitors recommended by Mark and these Wurth inductors https://eu.mouser.com/datasheet/2/44...022-539602.pdf as found by others. Nothing on backorder so hopefully I can have a few of these built before 2021


I don't know how good my scope will be to pick up the noise on my PC's power supplies to the soundcard and USB DAC but I'll see if I can come up with a couple of pics to show before and after. If not, just the listening impressions.


Thanks Mark for posting such an interesting filter & sharing the design.
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Old 13th December 2020, 03:10 PM   #236
joensd is offline joensd  Germany
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If anybody in Germany wants boards I'd like to participate,
Although ideally I'd like some mounting holes too.
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Old 13th December 2020, 03:58 PM   #237
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
@joensd, there are diyAudio members who lay out PCBs for sport and sometimes for pay. Poke around here and there, see if you can find somebody who is willing to give you a new layout with mounting holes too. My information could be outdated or just plain wrong, so approach these members with cautious respect, but I think @Prasi and @JPS64 and @jhofland might be possibilities.
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Old 13th December 2020, 04:33 PM   #238
joensd is offline joensd  Germany
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Thanks Mark for your guidance and advice!
Itīs easy enough to do a layout for myself but as I donīt need many of these I wanted to express my interest in case somebody wants to share.
Itīs more sustainable doing one order than everybody cooking his own soup as we say.
Iīll probably go with breadboard and see if I really need that much more.

But as Jan pointed out, this really is an invaluable tool in times of SMPS all around us.
The question is (and Iīm pretty newbiish here), how generic and how stable is this filter with all those SMPS out there.
How did you come up with these values?
Any particular literature you followed?

Jens
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Old 13th December 2020, 05:45 PM   #239
ClaudeG is offline ClaudeG
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Common sense :-)
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Old 13th December 2020, 06:01 PM   #240
joensd is offline joensd  Germany
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Unfortunately "common sense" is not necessarily common ;-)
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