Amp power supply questions, attributes

[jol50]

I wondered if someone who knows could summarize in general what one might recognize looking at a power supply in an amp. I find bits and pieces here and you can only tell so much by looks, but thought it may help to know if there are some generalities or 'rules of thumb' that apply?

For example I have a late 90s MTX (USA made) with 6 PS mosfets that is rated at near double the output of amps with a similar PS and similar age. Since faster (like many newer amps) operating PS are smaller, were they just ahead in technology? Are they running it closer to its limits? Better components? A combination makes it hard to tell by looks alone? I never heard of MTX over rating their output far as I know.

Some PS you can see the toroid core, others have the maximum amount of wire wound on them....does that tell anything important? Are dual toroid just a way to use lighter components on the board and/or cheaper than a single large one? Some older amps did that some not, now I see newer cheap amps doing it. Most of the big oldest old school amps seem to have used one large one.

Or am I just barking up a dead tree and there are many combinations that will produce a good PS to fit a particular situation?

[Eva]

The number of MOSFET pairs does not tell much because you can find them with Rds-on as high as .04 ohm and as low as .004 ohm. Cost reduction dictates the use of more devices having higher Rds-on most times. They use to buy huge lots of old surplus MOSFET...

Also, the quality of the switching circuit dictates how close to their ratings the MOSFET can operate reliably. For example, I only need a pair of IRFZ48V for 2x150W and I have even got 72A continous from a pair of these (push-pull, 50A rms per part).

The size of the transformers and style of the windings does not tell much either. You would have to measure winding resistances and leakage inductances in order to compare their grade of optimization. Note that to compare leakage inductances from different PSU they have to be multiplied by the switching frequency first.

I like small cores with 5 or less primary turns. These are operated around 50Khz. Bigger cores with more turns are usually operated at 25Khz.

[jol50]

Thank you for the insight Eva.

I'll have to read up on leakage inductance, might be a while before I design a PS but any info helps. Sounds like some type of testing would be a better way to identify how well a PS works.

It seemed quiet here and I was curious, always looking for ways to identify quality in an amp or lack of.