Clean SMPS for stompboxes

[spoontex]

Hi,

some time ago I built the AMZ power supply, and it's fantastic. But my linear power supply was broken and nowadays it's difficult to found some of this supplies. So I decided to use a laptop power supply, and now I have a lot of noise. I need to clean this noise a bit, and I found this circuit. What do you think about that?




http://www.muzique.com/tech/powr6.htm

Thanks.

[Rob Strand]

A filter like that always helps.  Often a bigger inductor gets rid of more junk but it is larger and more expensive.
The inductor needs to be rated at a current higher than the load current.  If not, the inductance will drop
under load and the filtering will (magically) become less effective.   (At very high frequencies the choice
of inductor and caps need to be chosen for the job.)

The filter you gave is the most common type to remove ripple on the supply.     

You can also get weird problems from common-mode noise.  The important thing is a common-mode choke is wound on the same core, it is not two separate inductors.   That lets the core be much smaller for a given current rating.  In some cases you can use two inductors but it is less effective and more wasteful in terms of the size of the inductor.   It's discussed here,

https://jandkaudiodesign.blogspot.com/2015/04/2-coil-choke.html

[spoontex]

The world of EMI filters is new for me...

The schematic that I uploaded rejects Differential mode noise, so I need to add another inductor for the Common mode noise. Have I understood correctly?

I have this one in my house:

https://www.mouser.es/ProductDetail/Murata-Power-Solutions/51504C?qs=sGAEpiMZZMsVJzu5wKIZCdoqB2Zv9TXDjjQOqaYz50s=

[Rob Strand]

The world of EMI filters is new for me...

There's a nice series of videos here,
https://www.youtube.com/watch?v=y-f_lxLI9ag&list=PLE3Pq-hBtiMS-1gFecr9FcBjf_p4joRZP

You can kind of get an idea from those videos *but* be very aware that he's talking about filters on the mains side.

The schematic that I uploaded rejects Differential mode noise, so I need to add another inductor for the Common mode noise. Have I understood correctly?

Your filter is a "single ended" filter.   It works very similar to a differential filter.   Normally a differential filter will have two inductors, one in each line.   It come about because on the mains side you have three wires.    For DC it's more economical to use one inductor.

I have this one in my house:

https://www.mouser.es/ProductDetail/Murata-Power-Solutions/51504C?qs=sGAEpiMZZMsVJzu5wKIZCdoqB2Zv9TXDjjQOqaYz50s

That's the thing.   Those types are fairly high current.  You can get smaller ones.

A large switch-mode power supply will very commonly have a common-mode filter on the mains side.   Very small switchmodes might use a simpler scheme.

The ripple is removed with the filter you posted.    It's just filtering, no tricky stuff.

The common-mode filter removes common mode signals which originate on the mains relative to the ground.   The common-mode signal flows through both DC wires then to ground.   This type of "interference" can get into circuits but it's not the same as outright filtering of ripple on the DC.  It's probably not worth adding it unless you are having problems. 

------------------------------------------
Here's where you might need a common-mode output filter,
https://www.eeweb.com/profile/recom/articles/output-filtering-part-2

To be honest, the reason why you would need one is not easy to understand.

[R.G.]

Rob is correct - cleaning up both differential and common mode noise from a switching power supply can be challenging, even for professionals. The pros expect to make several prototypes and tinker them to get good results, even with long experience in other designs. It can definitely be done, but be prepared to spend some time and money getting it done, especially with the common mode noise issues.

I'm naturally a do it yourself kind of guy, so it took me a long time to get to the point where I realized that some things are worth buying, not building. It's perfectly fine if you just like the tinkering to adapt your laptop power supply. But if the objective is to have a power supply instead of spending time working on a power supply, you can buy a known-clean internally protected 9V switching power supply for US$25 in the USA. One example of this kind of thing will put out 1900 ma (1.9 amps) of clean 9V. This can usually power an entire 9V pedalboard.

But if the objective is tinkering and the challenge, go for it. You will definitely learn some things.

[Bluenoser]

Thanks for the responses everyone. The layout is volume/gain on the top row and bass/treble on thec bottom. Doesnt sound like a Timmy to me, and smootjervtjan a TS type pedal. Closest guess so far as sound goes would be the Maxon 820.

Yes I live in Halifax