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jlind54 1st December 2012 09:21 PM

Power Supply Preference
What are real world pros and cons of using an offline dc power supply vs a simple transformer with a bridge rectifier and caps for a high powered amp supply? (by high powered I'm thinking something in the range of 1000 to 1500 watts out of a class d amp for subwoofer duty)

DUG 2nd December 2012 12:31 AM

By "offline dc power supply" do you mean an AC-DC switcher and the other a 60Hz transformer?

If so then the AC-DC is regulated (99.9% of the time) and the other will have a certain amount of ripple...unless regulated.

The AC-DC will have frequency components above hearing range. (IMHO...some people disagree). Whereas the 60Hz transformer will have frequency components at 120Hz and above (within hearing range)...

(But with good design neither of these issues with either power supply types will show up in the final output.)

With proper design the AC-DC switcher can draw current from a larger portion of the supply waveform...labeled as PFC type. Actually producing less of a current spike on the AC supply and less source losses. (small difference)

Biggest difference...overall efficiency...AC-DC switcher wins

Oops...and size...AC-DC switcher wins

...and heat...AC-DC switcher wins

simplicity...60 Hz transformer wins



qusp 2nd December 2012 12:51 AM

Ha yes i've come around too, nolonger are switchers an evil word for audio, the advantages now outweigh any possible negatives, provided they are well designed they can be quieter, more efficient and fully regulated for high power applications, which is a big advantage in my book

jlind54 2nd December 2012 03:05 AM

Thank you for the great information. This points me in the right direction to start researching. This may sound a bit dumb but would it be possible to bypass a car audio amp power supply with a home built solution with minimal side effects to sound quality assuming the built supply runs the amp rails at the same voltage and is able to supply the necessary current.

MarianB 2nd December 2012 12:02 PM

The advantages of swithcing PSU's over the linear ones have become more and more important so they are more and more used, this would be some of them:

-The production cost is less;
-The overall size is smaller;
-Theyr weight is less;
-Well Regulated voltage on the outputs on much higher eff.;
-Theyr better efficiency means less heat generated ( much less most of the times );
-Less influence from mains variations, meaning you can get the same power from much larger voltage range on the mains;

All of that comes at the price of much more complexity so a good design is much more tough to make.

PS: Yes, you can bypass a car audio power amplifier's PSU, you have to make sure the new unit generates the same VA characteristics and all should be good.

AndrewT 2nd December 2012 12:16 PM

I'll repeat the advantage of the linear PSU - Simplicity.

I believe there is an even bigger advantage.
Enormous short tern current capability. Easily 10times the rated continuous output current rating !!!!
Your 1kVA transformer with 60Vac secondaries is rated @ 8.33Aac and this becomes a continuous 4.1Adc after the smoothing capacitors. Short term current output can exceed 41Apk without any distress. And just as importantly:- the output voltage while delivering that transient, will hold up to within 90% to 95% of the rated output voltage.

Try to find an AC to DC switching PSU that can give +-90Vdc and give 41Apk while still maintaining >85Vdc on the loaded supply rail. I'll guess that a 4kVA switcher that has a transient capability of >=180% of rated continuous output current will meet the 1kVA spec of the linear supply.

MarianB 2nd December 2012 12:27 PM

The 50/60hz power transformer can handle more load current, yes, but at what price i ask you? well the unswear is that the output voltage will drop verry much with increase load current, that peak current you speak of can happen only on verry big loads or more like shorts on the outputs, well aside from the fact that the bridg rectifier diodes would most probably die, the output voltage will by no means stay nowhere near 95% percent the rated output, it is almost impossible to get that, and all of that would be with a sorf of huge power transformer, and ofcourse a verry expencive one, thus the SMPS gains more ground every day.

Mooly 2nd December 2012 01:04 PM


I've pulled some posts. You've made your points for and against. Lets not make it personal.

jlind54 2nd December 2012 07:19 PM

Taking into consideration the great information you all have provided it would stand to reason that the switching supply is they way to go. Next question would be are any particular layouts preferred over others. I’m referring to the switching portion. (transistor configuration)

single- transistor forward
two – transistor forward
half bridge
full bridge

I’ve noticed in reading that two-transistor forward and push-pull are common in computer psu’s

My gut instinct would lead me to believe a push-pull configuration would potentially be the easiest to layout and scale to meet power needs but I could be wrong.

benb 3rd December 2012 02:10 AM

Switchmode supplies (SMPS) for that much power include power factor correction if they are made to comply with commercial standards for "office equipment" of the past decade or so. Other supplies (whether it's older or noncompliant switchers, or the conventional Big 60Hz Transformer) won't have this, and may blow a mains fuse or circuit breaker due to the current they pull, even though they're not pulling as much power as the mains circuit is rated for. Not having power factor correction at this high power level is also bad for other reasons (for one thing, the ugly current waveform could cause extra buzz in other audio equipment), so there's just about every reason to use a SMPS with PFC. Get a commercial off-the-shelf SMPS with the appropriate output voltage and current ratings, AND with PFC.

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