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Ferrite/cap filter on the P24: next best thing too a full linear cMP setup? (interim report)

Hi all,

Since going all linear on the P24 is beyond my construction capabilities, I kept searching for some other way too improve the power supply too the P24 beyond the hybrid PSU solution I currently use (linear PSU + Pico on the P24).

* What is the next best option too a full linear cMP setup?
I noticed that amongst inmates it is communis opinio too consider PSU’s designs which are best for analog audio are also considered to be best for digital audio systems. But when reading about power supply noise suppression & decoupling for digital equipment, it appears that also much comes down too carefull and professional PCB design which addresses these issues on the PCB. Actually much of these issues can only be addressed locally on the MoBo. But how much of this is already done with sound quality in mind on a MoBo costing 45 euro’s? Clearly not much because when power supply to the MoBo is improved SQ greatly improves. But does this mean that analog audio and a cMP MoBo have same demands on the quality of power supplied?
Since the MoBo itself also generates lot of noise, delivering exceptional high power quality to the MoBo also might look like an attempt too make sewage water drinkable through mixing it with bottles best spring mineral water available. May be also less extreme PS improvements can still bring some further SQ improvements.

* Why did I try ferrites + caps?
Since constructing an all linear PSU is beyond my DIY skills, the only option left I could think of was some sort of filtering on the power that is supplied by the Pico or the Antec ATX. Articles on power supply noise suppression & decoupling all use some sort of LC filter constructions on the PCB. Mostly through of a combination of ferrite beads and caps. So why not try and see if this also can be applied on the output of the Pico or Antec?
Since I only can solder some kind of filter for use on the P24 line, the filter region can only be in the lower HF area’s. Filtering VHF and UHF can only be realized on the MoBo itself close too the IC’s through special design and using highly specialized parts.

I’m also not capable of doing any calculations on the use of wired coils/chokes (much too difficult) in filters. Especially the calculations on how too prevent ringing of coils/chokes are very complicated. So I was extremely happy that I stumbled upon articles in which ferrites where used in LC filters for noise suppression. Of course I already knew that clamp-on ferrites are being used on all sorts of signal cables and PS cables, but it never sprang too mind trying them on the P24 combined with caps too create an LC filter.

And lastly: ferrites are relatively cheap and it’s very easy too experiment with them on the P24 line.

* What I learned so far from 2 months messing around with ferrites.

1. Just 2 or 3 will have no audible effect.
When using ferrites (without the caps added) a ‘brute force’ approach is needed. At least some 5 to 7 ferrites in series on the P24 are needed too let you hear any subtle SQ improvement.
Although in a completely different situation, this ‘threshold effect’ is described in several articles and power points presentations on the http://www.audiosystemsgroup.com/publish.htm webpages.
The author suggests too clamp on at least 500 to 1000 ohms too get past this ‘threshold effect’.
‘Everything you always wanted too know about clamping ferrites on a wire’ is on these audiosystemsgroup webpages. Also much on proper grounding of your gear. VERY RECOMMENDED reading !
Also other authors report: ‘More is better’.
So put on the maximum amount of ferrits that will possibly fit in some way on your P24. Be creative in how too clamp a maximum amount. The longer the string of ferrites, the better. The impedance is proportional to length. This means that for a certain volume (and weight) of ferrite, best performance will be obtained if the inside diameter fits the cable sheath snugly, and if the sleeve is made as long as possible. A string of sleeves is perfectly acceptable and will increase the impedance pro rata.
See: http://www.elmac.co.uk/pdfs/ferrite.pdf

2. The effect on SQ is no less than ‘jaw dropping’ when creating a filter through adding caps.
The effect of caps used together with ferrites is shown in figure 5-13.
(see also page 38-39 http://www.murata.com/products/catalog/pdf/c39e.pdf )
Van on filtering, demping, ect


3. Use good quality low ESR caps.
The use of good quality, low ESR caps is important. See graph.
Van on filtering, demping, ect

I used Oscons

4. Filter all (!) lines/wires on the P24.
Noise might also creep onto the MoBo through the ‘STD-BY’-line, the ‘PWR-OK’-line and the -12V-line. So just to be sure I also put filter-caps onto these lines too.
However these lines don’t need bulk-capacitors which serve as a ‘current reservoir’. Extra bulk capacitors are only needed on the 3.3, 5 and 12 volt lines too suppress voltage fluctuation through extra current supply.

5. What values too use.
* Ferrites
I first used clamp-on ferrites with the highest possible resistance www.conrad.nl would sell. 172 ohms at 100 mHz. I managed too clamp on 15 ferrites on the P24. But this way I also ended up with ‘a huge pile off charcoal’ on the P24 connector. Leaving no space for caps after the ferrites too create an π-section filter.
So I ordered flat ferrite clamps for ribbon cables (132 ohms at 100 mHz) and an extra P24 extension cable. See picture.
Van on filtering, demping, ect

Carefully check if all off the combined P24 extension cable wires will fit into the flat ferrite clamp. I had too buy an P24 extension cable with extra thin 22 AWG wires too completely fit all P24 wires into the flat ferrite clamp. A P24 extension cable with 18 AWG wires (which are thicker than 22AWG wires) would not allow for fitting all wires into the flat ferrite clamp!
So carefully select the inner dimensions of the flat ferrite clamp for ribbon cable so it can accommodate all of the P24 wires.

Avoid DC bias / saturation
At saturation the attenuation effect of the ferrite core disappears.
To avoid this make sure that both go- and return- currents are of equal strength and both flow through the same core. Used this way the ferrite is not subjected to a net magnetic flux and will not saturate.
See page 109-110 http://www.steward.com/pdfs/emi/technical/Use%20of%20Ferrites%20in%20EMI.pdf

* Caps.
Since I’m not able too make any complicated calculations on what caps value’s too use in the π-section filter I had too find these values by looking at what values I saw being used in articles and papers ect.
The Murata paper recommends using value’s in a 10:1 rating but that still doesn’t provide any absolute value’s. By looking at what values also are being used in other articles and papers and looking at what Oscon value’s I could buy at Conrad I choose: 330 uF + 47uf Oscon’s (I liked 470:47 better, but couldn’t buy 470 uF Oscons at Conrad)

* L-section filter
Since this is project is still 'work in progress' and I’m still experimenting, I did not yet solder any of the caps onto the P24 wires yet. I just pushed the legs of the cap into the inside of the plastic P24 connectors. This way the caps legs can connect too the metal cable connecters inside the plastic P24 connector.
Too construct an L section filter I simply put a triplet of a Panasonic FC 4700 uF + Oscon 47 uF+ 0,47 uF polymer cap on the 3.3V, 5V and 12V section between the Antec and the ferrites. See Picture.


Van on filtering, demping, ect

The effect is no less than amazing !
Hearing is believing.
Much more micro details, imaging, soundstage, etc, etc.
So the usual SQ improvements one gets when improving the power supply but only this time in some nice amounts ! :-)

* π-section filter.
In the past I hardly noticed any SQ improvement when I placed (good quality) caps on the P24 lines.
Putting on the above mentioned triplets didn’t do much, if anything at all when placed them on the P24.
So I was really amazed that putting little 47uF oscon after the ferrites (thus creating π-section filter) now resulted in a clearly audible SQ improvement. See picture.
Van on filtering, demping, ect

Too put in perspective somehow: the 47uF Oscon caps after the ferrites improved SQ again by 15 % of the improvement that the tripplet caps placed before the ferrites (L-section filter) already had brought.

I wrote this interim report too encourage other inmates too experiment with π-section filters on the P24. In my setup an π-section filter made of ferrites + caps brought the usual SQ improvements but this time in GENEROUS AMOUNTS ! Highly recommended.

This is it for now. Do try this at home.

As always: any positive suggestions, comments, ideas, ect, which will improve the above suggested supply noise suppression on the P24 are very much welcomed


Mark



Edits: 07/07/11 07/07/11
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