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Audio Myth - "Switching Power Supplies are Noisy"

Mike Hanson

Mike Hanson

Trying to understand...
According to Benchmark Media (makers of the fantastic DAC1 and DAC2):

About 5 years ago, Benchmark stopped putting linear power supplies into our new products, and we replaced them with switching power supplies. We did this because linear supplies are too noisy. Yes, you read that correctly, linear supplies are noisy! A well-designed switching power supply can be much quieter than a linear supply.
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I'll admit that the DAC1 and DAC2 seem to have the lowest noise level of any piece of audio equipment that I've ever owned.

Read more here: http://benchmarkmedia.com/blogs/app...audio-myth-switching-power-supplies-are-noisy
 
Interesting take on the area. I'd agree with some points but think others are over-stated, etc.

Yes, big mains transformers can produce quite noticable external H *and* E fields. FWIW When I designed a power and pre amp mumble eyars ago we put a sheet of mu-metal under the lid of the power amp because we knew some users would plonk the preamp right on top of the power amp. The transformer was built to have minimised external fields, but there will always be some.

However I always felt that allowing an unregulated PSU to 'sag' under *extended* high power demand helped take some of the dissipation away from the output devices. And allows the peak powers available for transients to be a lot higher than if the rails never move. Decent music has a fair peak/mean ratio. So the real issue is that the 'rms' measurements in reviews understates what you can get for music. In effect a 'cosmetic' problem rather than a useage one.

But I'd guess the bottom line is - which kind of PSU is the designer more comfortable with and finds easier to develop to do the job? Not really a matter of one being 'inherently' better or worse, but which they can get to work best for what they're doing.
 
Equally, well-behaved SMPSUs can still produce quite hairy common-mode noise problems when you start interconnecting several (by hooking the products they power together)

I agree though, it's not that one or another technology is 'best' - which depends on application, project constraints overall, and how much you are willing to finesse the solution picked.

NB this article certainly does not absolve the average SMPS wallwart!
 
Yup, it all comes down to the the overall quality of the design. BTW, I just realized that the DAC1 had a linear supply, whereas the DAC2 has an SMPS. I guess I can stop worrying about it sitting beside my phono stage. :D
 
I don't have a Benchmark DAC. But I do have their ADC1 USB and find it works very nicely indeed. Certainly no complaints about the PSU! :)
 
The headline seems a bit misleading; to my non-technical ears, it seems the take home message is that switching power supplies don't have to be noisy, but many (most?) of them are anyway due to poor design. I.e., the "myth" of noisy SMPSs seems to have ample supporting evidence.

Maybe I'm missing something?
 
It`s all in the implementation, however it`s a good deal easier to make a linear supply that doesn`t cause problems with sensitive signal stages than a corresponding SMPS.
 
Its certainly the case that when I've neede a quiet PSU I've built linear ones. But that may tell you more about my age than it does about PSU design. :)
 
kasperhauser said:
The headline seems a bit misleading; to my non-technical ears, it seems the take home message is that switching power supplies don't have to be noisy, but many (most?) of them are anyway due to poor design. I.e., the "myth" of noisy SMPSs seems to have ample supporting evidence.

Maybe I'm missing something?
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This paragraph in the linked article sums it up.

SWITCHING SUPPLIES MUST BE OPTIMIZED FOR AUDIO APPLICATIONS

This discussion would not be complete without pointing out that many switching supplies are noisy. Older designs and low-cost designs tend to use lower switching frequencies that fall within audible frequencies. Many small cellphone and computer chargers fall into this category. These devices can cause interference when placed in close proximity to an audio component or cable.

The switching supplies used in Benchmark products are specifically optimized for audio applications. These switching supplies are much quieter than traditional linear supplies of similar size.
 
Linear power supplies require a lot more effort and care to get right and this increases the cost to produce. However once they are designed and implemented properly they easily out perform a SMPS by a long way.

There is only one reason a manufacturer will use a SMPS...
 
adamdea said:
This paragraph in the linked article sums it up.

SWITCHING SUPPLIES MUST BE OPTIMIZED FOR AUDIO APPLICATIONS
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Yeah, that and what follows it are the bits I was talking about. Perhaps a better headline would have been "Audio Myth - "Switching Power Supplies are Inherently, Unavoidably Noisy"".

But hey, it's just marketing, after all.
 
Occurs to me to mention that the main problems I tended to find in the past with using linear PSUs in audio kit was that many designs of mains transformer produce quite audible *mechanical* buzzing noises. Particularly when the mains power supply isn't perfect. At least the mechanical buzzing from SMPSs won't bother me, even if it does irritate bats. 8-]
 
kasperhauser said:
Yeah, that and what follows it are the bits I was talking about. Perhaps a better headline would have been "Audio Myth - "Switching Power Supplies are Inherently, Unavoidably Noisy"".

But hey, it's just marketing, after all.
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The thing is though, I do think there is an extant notion that SMPS are bad, and that the first thing anyone should so with an smps is replace it. I first came across this with the squeezebox touch smps. I remember that at the time it came out and people inevitably insisted that a replacement linear psu (of who knows what spec) was needed to replace it, the official position was that the old psus on the original squeezebox were a bit crap but they had taken trouble to clean up the ones with the touch and they were fine.
 
If you've ever dropped a well-designed and implemented, fit-for-porpoise, superbly measuring linear power supply on your foot you'll quickly learn that among other things they're quite painful.

Joe
 
Ha! I've a very odd shaped post-smash toe to prove that, where an SMPS of equivalent rating would have merely twinged in passing (It was just one Big Mofo Trafo; it delivered explosive dynamics and world class articulation of sweariness, I promise you that much. Also reduced my slew rate for a week or two.)
 
Joe P said:
If you've ever dropped a well-designed and implemented, fit-for-porpoise, superbly measuring linear power supply on your foot you'll quickly learn that among other things they're quite painful.

Joe
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I imagine they generate considerable amounts of noise, too.
 
martin clark said:
Equally, well-behaved SMPSUs can still produce quite hairy common-mode noise problems when you start interconnecting several (by hooking the products they power together)

I agree though, it's not that one or another technology is 'best' - which depends on application, project constraints overall, and how much you are willing to finesse the solution picked.

NB this article certainly does not absolve the average SMPS wallwart!
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Well stated especially the Common mode noise - BTW this is the noise output from a claimed "Low Noise SMPS" (Ignore the 8KHz USB artefacts) :-

https://dl.dropboxusercontent.com/u/86116171/Regen SMPS noise.jpg

You can see the "Spread Spectrum" trying to lower the "averaged" peak levels... While technically it is spread spectrum in reality with the SMPS you just end up with additional frequency components of the "Hopping" modulation stimulus. I've always considered that for Spread spectrum to be effective it needs to be Random.
 
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