The Truth About HiFi Amplifier Power Supplies

[Angsty]

Not sure if this was shared in the earlier pages, but it has appeared on ASR previously. Benchmark has some thoughts about linear versus switching power supplies.

Audio Myth - "Switching Power Supplies are Noisy"

This Myth Goes Something Like This: "Switching supplies are noisy." "Linear power supplies are best for audio." We disagree!

benchmarkmedia.com

 

[fpitas]

I've designed a lot of very sensitive electronics using switchers. It can be done.

 

[Punter]

Switchmode power supplies are fitted to just about every piece of sensitive medical equipment out there. If they were "noisy" and caused electromagnetic interference, they would be useless in that application. The golden ear brigade are so convinced that everything modern is somehow evil and that it is poised like a vulture, ready to steal your enjoyment of music that they miss out on equipment that has been designed and manufactured with modern thinking. How do they square this thinking when it comes to DAC's and streaming? Oh, the answer is, they allow snake oil peddlers to convince them that this equipment has all the same faults as stuff designed in the 70's and therefore needs special cables, routers, switches, etc etc.

 

[TimF]

As a result of comments on ARS, particularly by restorer-john, if I recall correctly, I got curious about ADCOM. I found a used ADCOM GFA 545 ii in very good condition and bought it. I've been listening to it for the last week and enjoying it. I'll keep it so I can occasionally alternate with it and a NAD class D amp. It's not hard to find good clean ADCOMS here in the USA, but then it's also not hard to find beat up worn down ADCOMS too. I know not to go poking around the insides of the ADCOM. In any event, thanks to restorer-john on steering me to the ADCOM.

 

[ahofer]

Somewhat OT, but I'm proud to announce that my son, with only a year at TI under his belt, has had his new power supply design accepted and built. For a consumer device from a very large company. It may well be tested here.

In his words, "everything in it has been done before, but they hadn't been combined in this way".

He sent me pics, but not my place to post 'em. Of course, it has to get through reliability testing....

 

[fpitas]

The toughest part of the design is picking the cord.

 

[solderdude]

Nah... it just needs to have some rope in there.

 

[atmasphere]

 

[Cbdb2]

I simulated current bandwidth ages ago: https://www.whatsbestforum.com/threads/power-supply-bandwidth.15198/#post-275474 -- have not updated and ported over here, think I decided not worth the effort. But when I click on the pictures "over there" to make them large enough to see I get a "not found" warning. I'll have to dig up the originals sometime.

However, the results are in line with what @solderdude showed, natch, so nothing really new or worthwhile. It was to show that power cord bandwidth for current needs to be a couple orders of magnitude greater than just 50/60 Hz, but not a MHz -- at least for a conventional supply. I don't have data for a SMPS; that might be interesting. Be nice to repeat on a Hypex or whatever class-D amp wall input and see.

4 pages in and finally the crux. Current spikes. Thats how a linear supply works. They can be huge in power amps and that can lead to noise issues. The output power and the transformer/filter caps dictate the current spikes, but the output impedance of the AC into the transformer (including the power cable and fuse) can have some effect.
So a resistor in the power line will flatten out the spikes (less current but you can still get almost the same power in, it just takes a little longer) and may make an difference in 50/60hz (and harmonics) noise pick up in an Amp thats not layed out properly, by keeping these large current spikes from inducing into the rest of the circuit.
So that expensive power cord is only connected 10% of the time. As is the power conditioner.