Simple SMPS test

Posted by: Simon-in-Suffolk on 20 January 2018

I thought I’d share here prompted by an article I was reading and my own experiences. SMPS are often incorrectly maligned, a switch mode powersupply can be as noise free if not better as an analogue transformer power supply if built and designed appropriately. But how do you know if you don’t have an EM/RF detector connected to a spectrum analyser? I know one can use one’s ‘ears’, however I am not sure how reliable that is unless powersupply quality is very poor given expectation bias and other variables. So a simple check is get a LW (MW or SW would work but not as ideal), and place right by the SMPS powersupply, and then try it’s mains cable and then it’s down stream low voltage cable ... turn on radio and tune around away from a radio station... can you hear any buzzing or rasping or other strange doors... you might also hear a rough tone that is slightly unsteady (this may be the switcher’s oscillator) ... any way if you hear such a noise that then stops when you disconnect the powersupply then you have found RF / EM noise radiating from the device... ideally you want no noise, but importantly you don’t want noise on the mains cable or down stream cable... Also if you hear such a noise irrespective of the SMPS you have other sources of RF/EM interference, that where strong should be investigated... this all affects our audio.

This an ideal test for EM/RF emissions and you can use for Ethernet and other electrical and digital equipment... and even some so called low noise regulated transformer power supplies , Ethernet/usb bridges etc....

Just a thought to share for the obsessive types, and perhaps helps prevents chasing rainbows.......

Posted on: 26 January 2018 by james n

Eloise posted:
james n posted:
Do you watch TV and listen to music at the same time ?
Only during Proms season... well and Glastonbury… when Later with Jools Holland is on… and for some Radio 2 concerts.
:-)

Yes ok - I do the same but for serious listening it's from local sources and with the TV off so don't worry about my Plasma (on the wall 2m or so from my kit) being an issue.

Posted on: 26 January 2018 by No quarter

james n posted:
No quarter posted:

This statement has me a bit concerned,my Panasonic plasma is mounted about three feet from my Fraim stack,What,if anything could this be doing to my audio equipment?
Do you watch TV and listen to music at the same time ?

Sometimes I mute the TV and listen to music,if a sporting event is on.I can not tell any difference with it on or off...maybe it is just paranoia. crazy

Posted on: 26 January 2018 by james n

No quarter posted:
Sometimes I mute the TV and listen to music,if a sporting event is on.I can not tell any difference with it on or off...maybe it is just paranoia.

Then you've no need to worry

Posted on: 27 January 2018 by Simon-in-Suffolk

Hi NQ, if you can hear no difference then fine... I could hear a slight robbing of micro detail when on, a typical sign of RFI. I could live with it.. but for serious listening the plasma went off. (Physically off as opposed to stand by).

HI Chrissu, I guess with modern living there is going to be some EMC pollution. it’s about being proportional, and keeping it away if you can from your audio equipment.. especially if more high end.

As far as fibre Ethernet, you probably know my view.. if done properly with quality SFPs and care and consideration given to minimum lengths then it’s fine.. but as Naim don’t currently support fibre it’s questionable what is being achieved other than creating a new random noise profile that may or may not sound preferable other than mitigating bad common mode noise from a cheap or errant network component. I suspect almost certainly it will be introducing clock noise to the Ethernet link... of course you might like the effect of this added digital noise on the analogue signal... the effects of digital noise can be strange.

Put your radio across your media converters and their powersupply leads ... if almost silent the chances are you won’t be adding common mode noise, however you might hear the effects of poor clock stability possibly as a faint unsteady tones on certain frequencies... if the other noise is quiet enough.. this is bad in my opinion as it can cause Ethernet physical layer clock intermodulation ... I believe I found this first when troubleshooting noise from a Netgear switch that was breaking into my Naim tuner.

One of the biggest noise culprits from networks I believe is from heavy broadcast traffic on your subnet....

Posted on: 21 February 2018 by ChrisSU

I've been wandering round the house with the LW radio again this afternoon, feeling like a bit of a weirdo, but nobody else is in! Some further observations re. sources of noise:

I still have a few fibre media converters on my network, and these do make a bit of noise. Not the worst offenders, but not silent. A couple of them run on iFi iPower PSUs, which were a little noisy, despite the manufacturer's claims (if they're that good, why do they need a ferrite on the DC lead?)

I have a Cisco 2960 connected to my NDX, and this was probably the only electrical device in the house that seems to be absolutely dead silent. I guess that's a good sign. Curiously, I have a Cisco 300 series switch at the other end, and this is very noisy, so I might have to investigate it a bit further.

As well as iPhone chargers being quite loud, my iPhone is noisy when active, with no lead connected. Maybe miniaturisation makes noise harder to mitigate, as my MacBook isn't as bad.

Light bulbs - some of these are awful. I've recently put in a number if 'filament' type LED bulbs, and these are very quiet, with the exception of a single Tesco own brand one, which sounds like a tractor. As do the few remaining compact fluorescents I still have. Time to ditch those, I never liked them anyway!

Does any of this noise actually do any harm to sound quality? Hard to say, but I'm going to try and eliminate some of the worst offenders, anyway.

Posted on: 21 February 2018 by ROOG

Good point about the LED lamps, SMPS are creeping in everywhere, may have to stock up on HiFi incandescent types.

Posted on: 21 February 2018 by Massimo Bertola

Good, another source of paranoia. This Wednesday was becoming boring.

Posted on: 21 February 2018 by Simon-in-Suffolk

Chrissu, interesting post and your point about ifi power supplies is spot on.. especially about the need for ferrite chokes

Also interesting about the switches, and your point illustrates perfectly what I have said before... just because a switch says ‘Cisco’ on the front, it doesn’t make it ideal for our uses.. it’s the type and model that is more relevant... and also your show SMPS can be designed to produce almost no noise at all as you found out.... SMPS’s are not automatically a bad thing... the 2960 uses a quality SMPS.

As far as affecting SQ... well it creates noise on the mains or connected cabling... this noise can pollute our audio systems.. whether you hear that pollution is going to vary from person to person and system to system I guess...

Posted on: 21 February 2018 by ChrisSU

Simon-in-Suffolk posted:
As far as affecting SQ... well it creates noise on the mains or connected cabling... this noise can pollute our audio systems.. whether you hear that pollution is going to vary from person to person and system to system I guess...

I'm curious as to whether the cumulative effect of all these noisy devices adds up - in which case eliminating any devices that are a bit noisy might help. Or is it more the case that a single, very noisy device might be powerful enough to reach the audio gear, and only that is worth eliminating?

Posted on: 22 February 2018 by audio1946

in theory electronic devices noises can cancel . i suspect not in multiple systems .best served to eliminate the biggest culprits