If you are looking for a really good USB power supply for audio devices, because all other power supplies are humming and buzzing, then the following is just right (and expensive): AQVOX power supply
I bought one of them for my MicroDexed, because the mobile phone power supply simply produced an ugly side noise and I am very satisfied.
Regards, Holger
But does it work with Zynthian? Only 1A?
A properly designed raspbery Pi PSU seems to need to be able to sink about 3Amps to be really stable and I’m not sure the micro USB connector itself is up to handling that sort of current reliably.
I use the hifiberry amp+ which drives theraspberry pi from the amp board and is fed with 18V at 3 amps to allow it to do 60W but I still think it could do with more.
Perhaps a 12Volt lead acid cell with a decent meaty 5V regulator is the answer . . . .
This reminds me of the ‘low oxygen hi-fi speaker’ cable urban myth… If the circuit design is good then what problems could USB 5v generate?
often cheap trumps good
That is what I was thinking, too, but maybe @C0d3man Holger hasn’t have time to test it, yet. I have the official Stontronics 2.5A power supply, and I just ordered a 5V/3A Voltcraft power supply to test with the all power demanding Pianoteq.
Would you recommend to me using a small PCB voltage regulator/step down converter inside the zynthian box and power it from a leftover 12V/3A external power supply?
Crawling the raspberrypi forum there are not so many threads regarding power supplies for real audio solutions like zynthian. Searching this forum I find lots of user entries but not so much links to used power supplies.
Maybe we could make a wiki entry for recommended power supplies?
Thanks for listening and God bless, Marius
In fact I have a problem to test because one Zynthian is “on the raod” for tests and the second “disco” one is mounted deeeeeeeeeeeep inside a rack 
My contribution was also not directly related to the use of Zynthian, but rather a general hint that USB power supplies can cause a lot of (audio) trouble. The Raspi/Hifiberry seems to compensate this quite well so far.
I only filtered the power supply of my TeensyMIDIAudio board (for MicroDexed) relatively simple. It’s ok, but you really have to pay attention which power supply you use. With the Aqvox power supply it is absolutely silent - and luckily 1A is enough.
Hm, probably both is ok, although a step-down converter can produce additional “noise”. That really depends on a try and I tend to work as little as possible with converters. Don’t forget, the Raspi addidionally converts 5V->3.3V.
Try Google for interference suppression solutions for audio systems to be powered via USB: Yes, there are a lot of ideas, but none of them satisfied myself for 100%. I think you just have to try (and have a scope within reach 
).
Regards, Holger
Hm, I think there is quite a difference…
A car battery with a LM1084 on a very substantial heatsink . . .
… if you want to be sure and have no scope: that’s a good way.
I think one of our 150Ah UPS batteries would fit also…
In every test I’ve done on many 5V powered audio devices, a small (in size) 1F 5.5V supercap has always been enough to transform a cheap power supply in a perfect one. And without need for a forklift… 
Is an additional resistor required to limit the current when switching on?
Regards, Holger
An inrush limitator should exists, but an inline resistor worsen the overall performances of the supply circuit, so a start circuit should short it after power on.
…but I’m too lazy for that, and count on the current limit of the voltage source
Thanks @Axeman and @C0d3man for the 1F 5.5V supercap tip,
what do you think of UBECs like this
It is used originally for LiPo accumulators, so would you recommend it in use with a 12V 3A power supply?
Thanks in advance and God bless, Marius
For what specific reason would you use it?
To use it with an unused 12v3A power supply for my zynthian. I would put it in the zynthian box and use it instead of the mini usb power connector. Another idea I was thinking about is a small LC circuit to minimize the ripple noise as is with the MOD Duo…
What do you think?
God bless, Marius
BECs are tailored to filter RF interferences that could break radio links. Its filters does almost nothing to the noises in audio band. But you could use it adding filters.
I often use automotive modules with 12V supply. Some are expensive, some are really cheap and Amazon or BangGood have many of them in stock.
Even with those some filtering should be added.
