what's a good power supply?

myleftear

Member
Paid Member
2017-09-10 6:33 pm
Luzern
Hello everybody

Being fascinated of all diy and audio, I try hard to follow all these very elaborated conversations. Problem is, I haven't the experience to understand it.

I built my ACAmp and am very happy with it, but—of course—want the project to continue, mind you :)

Next steps are to build another one or two and run them bridged/parallel, and to tweak it as suggested here and there. Many are saying that a great improvement can be made with the use of a good PSU...

But, what exactly IS a good one? How do I identify a good (or not so good) without spending money on it and trying it out (that is, by reading the specs and stuff)?

You know, is this (MeanWell 24V150W) good enough, or that (another one) , or should it be some shiny high end mega-beast like that?

Oh, and don't worry, I'm being cautious, and won't burn down the house. I'm just reading (yet).

Thanks very much!
 

ubergeeknz

Member
2018-08-31 12:32 pm
I believe a good power supply:

1. Has the required voltage output for the application

2. Can provide all required current for the application

3. Has a low impedance within the operating range (that is, the voltage stays much the same regardless of current drawn)

4. Injects minimum ripple and noise

Ideally, a power supply would have the exact voltage you want, zero impedance, an infinite current capability, zero ripple, and no noise.

But of course these things are impossible so it becomes a balancing act between cost and meeting or exceeding the required performance parameters.
 
To the above good list I will add from practice and for audio amplifier use a regulator with "fast load response". Fast load response means the ability very fast to establish the nominal voltage when the loading is changed. When the load current is suddenly increased or decreased, the regulator circuit will have to adapt the output current to the new loading in order to return to the nominal voltage. Some regulation loops react fast, some much slower. The need for fast reaction heavily depends on the speed at which the load changes and also the design of the power stage. Audio power amplifiers (except pure class A) are very fast changing loads that may make an else low noise power supply change heavily in output voltage due to constant changes of the load current. Changes in output voltage influence amplifier distortion and thus sound quality.
While most other parameters are specified in the power supply specification sheet, load response is more rarely addressed.

A current limiter may be a very useful feature, in particular for a laboratory supply. The current limiter serves to protect the power supply and often also the load from destruction.
 
Good (class A/B/AB) amps generally have good PSRR and place little demand on the power supply other than they supply the power demanded (ie the first three bullet points of post #2).
Lower quality amps place greater demands on the PSU to compensate for poor PSRR.

Class D can be another matter, some demand very quiet supply rails, others compensate for variations in supply voltage to various extents.

Basically high PSRR in the amp, simple supply will work well, poor PSRR in the amp, PSU has to nurse the amp into performing.

Switch-mode PSU's can be an issue with high frequency noise they generate intermodulating in an amp. Probably no simple rules of thumb here.