Suitability of a power supply for audio

[Alialiali]

Hi everyone,

I have a few Meanwell 350W 24V DC power supplies [1]. I don't see this kind of power supply used in audio projects ever, and I wonder if there is a reason for it, and if so how I can mitigate the problems. I have used it on an cheap amp board from AliExpress and it sounded not entirely awful.

In general I am not going for sound quality, but I need 40 of these units, so price is really important. Power supply+amp+speakers+bluetooth

Thanks for your help.


[1] https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF

 

[KatieandDad]

If you are not going for sound quality then they will be fine. I would add a small inductor and a further filter capacitor close to the amps to reduce HF noise.

 

[abraxalito]

They work fine, they can even sound very good with additional filtering. As you don't care much about sound you can use them as is.

Incidentally Meanwell is a respectable Taiwanese brand of SMPSU - if you care mostly about price why not go for a mainland Chinese vendor, they are cheaper (but generally of lower quality). For example Weho : ????350?LED???????350W??24V14.6A?2?S-350-24-???

 

[Alialiali]

Thanks for the speedy responses. I'll certainly check those cheaper PSU - thank you.

About "additional filtering" and "small inductor", could you please help me on the how and where? I imagine capacitors of 1000uF, 100uF, 100nF (guessing numbers) between VCC and GND, but not sure about the inductor.

Thanks again.

 

[Vovk Z]

10-47 uH, somewere between PSU and amp.
100-1000 uF Low ESR type cap (this one can sit on your amp power input).

 

[Alialiali]

Thank you, very helpful.

 

[Pano]

Meanwell makes a wide range of power supplies, and many of them are well liked for power amps. I've used models from 12V to 36V and found them to be rather good.
There are something of a diy favorite.

 

[Elvee]

I don't see this kind of power supply used in audio projects ever, and I wonder if there is a reason for it, and if so how I can mitigate the problems.

Some SMPS's designed explicitly for audio applications do exist, and unusually that's not ordinary audiophoolery (although this factor might creep in).

Let's take a simplified numerical example: you need to power an ideal 10W class B amp using such a supply.

Theory tells us that the efficiency of such an amp driven at its max is π/4~=78.5%.
This means that you need to supply 12.7W of average DC power input.
If, conveniently, your PSU has an output voltage of 12.7V, you will need 1A DC.
For such a supply & power, the load resistance is U²/P, U being the rms output voltage: 12.7/2√2, thus ~2Ω.

Now, if you compute the peak current going through the supply, it is 0.5*Vs/Rload, and 6.35/2 is 3.15A, thus more than three times the average current.

If you try to draw such a current at a low frequency (where most of the program power is concentrated), say 20Hz, your 12.7W supply is going to crumble twice per cycle, with disastrous audible results.

This example is simplified, and looks exaggerated, but reality can be even worse because of reactive currents.
I gave a class B example, but except for some class A, the problem is the same for all types of amplifiers, including class D: no amplifier has an energy storage capability (not enough for 20Hz anyway)

The problem arises because the supply's protection kicks in very quickly when dangerous levels are exceeded, which is normal for a regular supply.

You could think that adding energy storage, in the form of a large parallel cap for example could solve the problem. Not so: the regulation is extremely tight, meaning the internal resistance is small, and the capacitor would need to be really huge to make a difference, but much before that, it will cause problem during the start-up phase.

Audio supplies are designed taking into account these constraints, but if you use a regular supply in this role, it needs a severe derating: typically a 10W amp would need at least a 50W GP supply.

Note that if you use an insufficient supply, problems won't be noticeable at "normal" listening levels for "normal" music programs (not too much bass)

 

[Simon1972]

100uh then 100uf tant and 1uf film in parallel into 1 ohm resistor to -.

Reduce SMPS ripple noise for PreAmp?