Quality Power Supply

[tago]

I'm looking for an appropriate power supply to minimize jitter with pots/faders.

@Zam worte in another thread:

Quote

 

Keys for low jitter:

-A perfect grounding, with same 0V reference for both servo and AD chips Vref

-Quality power supply with low ripple, good line and load regulation, optional sense is a must

-shorter wire as possible

-optional low pass RC filter can be added

 

 

Can you recommend a ready to use power supply? I'm have no idea how to build one myself. Would i tbe simple to build one myself?

 

[tago]

Would this be good enough?

http://www.ebay.de/itm/AC-DC-5V-3A-Low-Ripple-EMI-Isolated-Step-down-Switch-Power-Module-Buck-Converter-/291810357129?hash=item43f140af89:g:L6EAAOSwuhhXU5j5

Ripple and noise: <100mV

[tago]

If i understand @Zam correctly, powering via USB is ruled out, right? That would have been newbie friendlier.

[Hawkeye]

You can probably filter most low-specced switching PSUs (I'd consider the ebay link one, based on the price, it is also unclear if that switcher operates on a low switching frequency, which might add more noise) with a bank of capacitors or a LC/RC filter.

Many MIDIbox users had successes with Meanwell switching PSUs, why don't you take a look what you can find? Then buy it, maybe attach it to an oscilloscope under load and check for ripples?

A good choice would probably be the meanwell rt-65b - it costs around 25€ but also has +12v/-12v, which you can use for modular stuff, or when you build an extender/fx unit, that uses opamps with bipolar power requirements.

Please be aware, that some switchers have minimum current requirements before they operate properly.

Many greets,
Peter

[tago]

16 hours ago, Hawkeye said:

Please be aware, that some switchers have minimum current requirements before they operate properly.

Thanks, Peter. Do i have to estimate the expected total current draw? A 60Watts power supply seems a bit high to me. Since i do not plan use it for more than the controller, should i get a smaller power supply?

USB2.0 is 5v*0,5A. Do you think 0,5-1A would be sufficient and better suited in my case?

Edit:

Reichelt has this 5V/3A Meanwell: http://www.reichelt.de/Schaltnetzteile-bis-150-W/SNT-RS-15-5/3/index.html?&ACTION=3&LA=2&ARTICLE=137080&GROUPID=7264&artnr=SNT+RS+15+5

Would you recommend that PS?

Edited July 27, 2016 by tago

[tago]

Or the Meanwell PS-05-5 5V/1A

http://www.ebay.de/itm/Meanwell-Schaltnetzteile-PS-05-5-5V-1-0A-/251537064348?hash=item3a90c7019c:g:k1sAAMXQ3kNTfINn

[Hawkeye]

Hi there,

if you only need 5V and are building a rather small controller, 60W is indeed overkill and both alternatives you listed are good. But I'd recommend to go for the 5V/3A Meanwell version... good price, it has a metal cage, and i've just looked in the datasheet: it seems to have a 132khz switcher, which is good (above the audio frequency), even if you use it on a plain digital controller with no audio elements.

You can improve the switcher ripple by adding a 0.1uF and 47uF capacitor pair in parallel at the end of the supply wire (i.e. close to your controller core), that would be very recommended.

I've read nothing regarding a minimum current requirement for that switcher, so you should be good, your MIDIbox will draw a few hundred mA, so all will be well.

Good luck and please report back, when you've installed it!

Peter

[tago]

@Hawkeye Thank you very much for your advice.

I'd like to understand one more thing. Should i go with two power supplies in my system? One powering digital stuff and one for analog ins (in my case AINSER64)?

Someone on TI forums says:

Quote

Digital things are noisy, they usually creates voltage ripple on digital supply (and ground) bus. That's why for precision analog circuits it's good to have separate (analog) supply which will be much "cleaner" than digital supply. Low noise analog design needs not only clean supply but good PCB layout including proper ground plane design and proper decoupling of both - digital and analog supplies.

https://e2e.ti.com/support/microcontrollers/msp430/f/166/t/285794

The Teensy for example has AGND and GND. How is this handled with Midibox and how this related to "digital"/"analog" power supplies?

[Hawkeye]

Hi there,

afaik, we only have common ground - and using a high quality filtered switching PSU should not cause too much trouble. Even though digital in design, the MIDIbox circuits should not behave like anything switching and power hungry in other digital domains (like e.g. powerful computer CPUs under high power load/no load, switched many times per second). Of course, there might be "power spikes" when LEDs in matrix configuration are switched at a higher frequency. But I think, this should be possible to handle with a couple of capacitors in parallel just ahead of your "sensitive" analog circuitry. Your best approach is: test. If it does not work as expected: measure. If you see ripple/spikes: filter. If all of that does not work, report back. But: don't worry too much... others have built MIDIboxes with lots of pots :-). And while there are resolution limits, you should be fine...

Best regards,
Peter

[tago]

3 hours ago, Hawkeye said:

If it does not work as expected: measure. If you see ripple/spikes: filter. If all of that does not work, report back.

You mentioned an oscilloscope earlier. Unfortunately i don't own one. What specs will i need? I'm afraid i can only afford an old one. I suppose a high scan frequency will be important. Can you recommend an old scope? What's up with Hameg 203 or cheap China scope (DSO138 or DSO203)?

Edited July 27, 2016 by tago

[Hawkeye]

Yo man, there have also been discussion threads about oscilloscopes on here, we can't cover everything in one thread :-)
I've got an old Hameg 203 and it is sufficient, a modern digital oscilloscope would be better, but you can actually still use these old 80s electron tube scopes, they will work well enough for ripple detection and should not cost much more than 50 euros :-)

Good luck!
Peter