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Author Topic: RF switchmode Fix  (Read 3984 times)

phatt

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RF switchmode Fix
« on: August 30, 2016, 09:21:21 AM »
It seems the world is destined to be run by Switch Mode power supplies and as iron core transformers
are now rare to find one has to put up with the short comings of this new  technology.
Yes they are light and cheap but I very much doubt their life span will even come close to the
old copper and iron transformer which can last indefinitely.

I'm posting my finding as I've had a few Smode supplies give me grief.

The main issue with these type of supplies is the high frequency switching introduces
some very aggressive RF hash and although some better designed units work OK for Audio,, a lot don't. :grr

I use a small Boss brand 9VDC 1Amp SM supply to run a few pedals which to its credit has worked
well for 3 years now but I have no spare supply pak and I know one day it will fail.
I recently acquired a 9VDC 2 Amp SMode wallwart,, $2 at a jumble sale but it comes with the dreaded RF whine :duh :grr
So I thought I'm going to research this problem as my Boss unit works noise free,,, sooo,,, there must be a way to fix this confounding problem.
After a couple of fruitless nights searching for some plain and simple explanations of the problem
and how to fix it I finally found this page;
http://ka7oei.blogspot.com.au/2014/08/completely-containing-switching-power.html

Well worth a read if you wish to understand what the problem is and How to fix it for minimal cost.

I'm in the process of testing this idea and after a few trips down the local electrical repair shop I've snaffled enough bits from scrapped white goods to make the two filters. Just ask before you raid there rubbish bins,, just watch out for micro waves and like white goods as some store voltages. 8|

It only took a couple of hours to establish that the idea works. :dbtu:
If any of you technical folks wish to add advice feel free as the maths involved for inductance is a bit over my head. The small donut inductors read 22mH on my meter ,, if I'm reading it correctly? I used 2 in series and the capacitors are 1,000uF. I was pushed for space so I left out the 100nF ceramics.

Meanwhile,,here is some pics of the process.
cheers all ,Phil.

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image posting

photo hosting
« Last Edit: August 30, 2016, 09:27:29 AM by phatt »

Loudthud

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Re: RF switchmode Fix
« Reply #1 on: August 30, 2016, 01:11:14 PM »
The one thing rarely mentioned is that most of these supplies will operate from 100 to 250 VAC 50/60Hz input. You just need the right Mains cord or an adapter. I found a 48V 2A but haven't tried it yet.

phatt

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Re: RF switchmode Fix
« Reply #2 on: August 31, 2016, 04:46:48 AM »
Yes ,,they is clever little buggas,, but it pays to read the fine print because some don't take both voltages.

I've got it all together today but too late to take pictures. :'(
All working and I can't hear any sign of high pitched whine,, though for a split second you power everything there is a bit of hi pitch whizz as it powers up but runs dead silent. :dbtu: :dbtu: :dbtu:

Now to do the same for my Korg Keyboard SMode power supply as it also bleeds RF through the line out. :trouble
Phil.

Enzo

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Re: RF switchmode Fix
« Reply #3 on: August 31, 2016, 01:56:31 PM »
Ever compare plain old Boss transformer adaptors versus same voltage generics?  The Boss ones are quiet, while the common ones hum.  Why?  Simply because the Boss ones have better filtration inside.  Boss pedals are made with the idea the well filtered Boss adaptor will power them.  Use a generic 9v adaptor on your Boss pedal and you get hum.  Other brand units do not expect well filtered power and so include more filtration in the unit.



Some SMPS will be quiet because they have good filtration on their own.  other SMPS are not all that well filtered because the things they are intended to power have all the filtration internally that is needed.  Remember, it is the system, not the parts.

Your cheap SMPS is noisy because the thing it was originally made for had sufficient filtration inside to make useful power.  Adding external filtration takes the place of this, yes, just as adding external filtration to a cheap generic transformer adaptor would make it quiet in an old Boss pedal.

phatt

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Re: RF switchmode Fix
« Reply #4 on: September 01, 2016, 05:11:26 AM »
Yes my Boss Smode supply Obviously has better filtering and you would think that any brand that is meant for Audio use would have the added filtering but my Korg Keyboard supply is not as good as the Boss supply.

You don't notice it much through the builtin speakers but when I tried to use the line out into a professional PA a while back,,, the hi frequency bleed through was instantly evident, :grr needless to say it Really stuffed up my day. I thought it might be the midi clocking or onboard processing but I now realize it's the supply.

I have no idea what the Daichi brand supply pictured was used for but it clearly states *Audio and Video power supply* so one would assume it was correctly filtered. Obviously Not.

It seems Pedals have always been powered by wallwarts (plugpaks in my country) and most often they have no ground, or at least the Mains ground is not connected through to the common of the secondary 9Volts.
This helped to avoid ground loop hums and all was good. 8)

I've noticed that with switchmode power you get gawd awful switch buzz if you plug in your guitar cord with the volume up on the Amp.  :o :o
(And that is with the good Boss supply) :-X

Interesting as this did not happen with the old iron transformers.

What I've done is ground the Common of the pedal board setup back to mains ground and now it's dead silent when you plug in a cord. <3)
Ground loop hum is no different with or without,, so I'll leave it grounded as it makes for silent hot plug swaps.
Phil.
« Last Edit: September 01, 2016, 05:12:31 AM by phatt »

Enzo

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Re: RF switchmode Fix
« Reply #5 on: September 01, 2016, 05:47:55 PM »
Quote
so one would assume it was correctly filtered. Obviously Not.

Not necessarily, as I clumsily explained above.  The power adaptor, whatever type, is part of a system.   All power supplies need sufficient filtration, but it doesn't matter where it is, you can have a really well filtered adaptor and a not much more filtered unit it powers.  OR you can have a minimally filtered adaptor and a well filtered unit.  Whoever designed the system chose where to put his filtration and chose an adaptor as appropriate.

So the fact it says audio and video power supply says nothing of how well filtered it is.  It only means it is appropriate for that sort of duty.  The amount of filtration it has plus the filtration in the unit it powers TOGETHER add up to the total filtration.  You can't take either one out of context and generalize.

So your Daichi was correctly filtered, but only for the application it was originally intended for.

galaxiex

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Re: RF switchmode Fix
« Reply #6 on: September 01, 2016, 07:08:51 PM »
Quote
so one would assume it was correctly filtered. Obviously Not.

Not necessarily, as I clumsily explained above.  The power adaptor, whatever type, is part of a system.   All power supplies need sufficient filtration, but it doesn't matter where it is, you can have a really well filtered adaptor and a not much more filtered unit it powers.  OR you can have a minimally filtered adaptor and a well filtered unit.  Whoever designed the system chose where to put his filtration and chose an adaptor as appropriate.

So the fact it says audio and video power supply says nothing of how well filtered it is.  It only means it is appropriate for that sort of duty.  The amount of filtration it has plus the filtration in the unit it powers TOGETHER add up to the total filtration.  You can't take either one out of context and generalize.

So your Daichi was correctly filtered, but only for the application it was originally intended for.

Which begs the question....

Are there any S-mode generic supplies intended for audio devices that are well filtered no matter the (audio) application?

....or are these types of supplies all device specific?

Just kinda thinking out loud...  ;)

Edit;

Hmmmm, thinking about this a little more, I realized that my One-Spot wall wart is a smps intended for effects pedals
and when used with any of my Boss pedals it does not "seem" to make them noisy. At least not that I can hear.

OTOH, I bought a Electro Harmonix pedal that came with it's own supply, and when used with the One-Spot instead, it was very noisy.
I had to use the supply that came with the pedal.


Edit 2

Did a quick search and found this....

https://benchmarkmedia.com/blogs/application_notes/152143111-audio-myth-switching-power-supplies-are-noisy
« Last Edit: September 01, 2016, 07:30:54 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

Enzo

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Re: RF switchmode Fix
« Reply #7 on: September 01, 2016, 08:15:23 PM »
Yep.

Any form of power supply can be noisy.  We surely have all heard linear supplies that hummed or sizzled with rectifier noise.  And while all the top end mixers and rack gear have SMPS these days, we can surely find noisy ones of those.  The bottom line is that noisiness is not determined by the technology of the supply, it is determined by the system.

phatt

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Re: RF switchmode Fix
« Reply #8 on: September 02, 2016, 03:15:37 AM »

Yes I see your point.
Sadly it was hard enough with the iron supplies as some were half wave recto and some had only basic cap filtering.

Now it's almost impossible to know how well a Smode is going to work with the equipment you wish to power.

My Korg Keyboard Smode supply is obviously on the cheaper side and If I was not electrically inclined I'd be lost as to how to fix the issue.

My friend just recently purchased a Trio pedal and the first time he used it on stage he had massive buzzing issues. Brought his gig to a screeching halt (was that a pun?) :cheesy:

It worked at home but the gig required him to plug into the house PA.
Once he removed the Trio from the pedal chain everything worked as per normal.
His Boss brand Smode was obviously not up to the task.

One thing I would mention (although not a noise problem) there is a Potential safety issue lurking as I've had quite a few of these switchmode supplies (Often Dead on arrival) and I notice the mains traces on the Pcb are Frighteningly close to low voltage pcb traces.

I think the general rule for 240 Volt board design is minimum 6mm between traces and some that I have pulled apart certainly have not read the recommendations.

Enzo I'm all for the idea of Smode power but NOT if it's a lottery as to which will work with what.
 
Phil.

phatt

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Re: RF switchmode Fix
« Reply #9 on: September 02, 2016, 08:06:03 AM »

Which begs the question....

Are there any S-mode generic supplies intended for audio devices that are well filtered no matter the (audio) application?

....or are these types of supplies all device specific?

Just kinda thinking out loud...  ;)



Well said, and that IS the Big problem there is no clear and well defined definition of the device and it's ability to supply clean DC.

Thanks for the link,, Yes I have no doubt that *IF* done right then it works but that would come at greater cost.

My understanding is thus; Iron and Copper transformers have one massive advantage, Reliability. I very much doubt that even the best designed Smode supply will still be working in 40 Years time.
20 odd years back I mentioned SMode supply issues to a well respected Amp teck in Brisbane and his answer was well there is nothing wrong with the idea but they are not as reliable. His main repair issue was trying to source parts for them. :(

Only 3 years back I had a chap bring me an Amplifier with 333 on the front panel, only 2 years old and just went buzz and died. 3 work shops worked on it before me and between us we eventually got some info from the maker.

Oh yes we have the schematic for the audio circuit but they admitted they sourced the Smode power supply from some far east company which no longer exists and we don't have a schematic for the supply,, sorry we can't help you. If I recall right some of the active devices were not even on the international register. So needless to say I would not recommend that brand even if the BS valve section was designed by soldarno.

There must be countless ways to build a SMode circuit and infinitely more mosfets and like parts to use. so trying to keep track of all that for a small concern is impossible.
whereas ye old reliable transformer there is only a handful of ways to derive DC from the secondary and they are all well understood. Trying to track down some obsolete timing chip or special Mosfet is going to render a lot of otherwise good gear useless. :loco

Regards your  "Electro Harmonix pedal" much like the TC electronics Trio I mentioned,, it works with its own supply but not with the Boss supply. I think this problem will just get bigger. :duh

Rant over..
Phil.

galaxiex

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Re: RF switchmode Fix
« Reply #10 on: September 02, 2016, 08:07:59 PM »

I think this problem will just get bigger. :duh

Rant over..
Phil.

Yep, I think so too, based on what I'm seeing and reading the more I look at these smps.

As an aside, that EH pedal is the C9 organ machine.
Fairly expensive pedal. I would have thought it would have better filtering built in.
I guess all the money went into the digital trickery.  ;)

The included EH supply is a bummer in a way...

I have only a few pedals that I use now, and did not want to "have" to use yet another wall wart dedicated to just one pedal.
Esp since my One Spot is capable of powering several pedals.
Oh well, I don't even use the C9 much... maybe I'll sell it...
If it ain’t broke I’ll fix it until it is.

Enzo

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Re: RF switchmode Fix
« Reply #11 on: September 02, 2016, 09:49:52 PM »
We are all guys with screwdrivers, and we expect to be able to go buy any supply and make it work with any unit.   But the OEMs make units and they also provide the appropriate power supplies for them.  SO when we say it will only get worse, I think that mostly means for guys like us trying to fudge odd supplies into systems.

There are examples of specific systems that have a no longer available part.  But mostly, if you want reliable power and no guessing, you spring for the real OEM power adaptor.  SOME -9v adaptors will power a Boss pedal cleanly, some will not.  But if I get a real Boss adaptor it ALWAYS works right.

We can complain that some SMPS was a commodity part from some secondary supplier to the OEM and is NLA.  But SMPS are not alone in this.  How many delay pedals are out there hoping to find a new SAD1024?  Of Synths needing various custom ICs or hybrids?


I had a customer one time with a noisy wrong adaptor for his Boss pedal, and he didn;t have another Boss adaptor, but he did have a gig that night.  Instead of making an external filter, I just opened the pedal and added some caps inside it.