possible to eliminate switch mode noise in headphones using passive components? - Page 1
Forum section: electronics / beginners

author: josephpate
author_rank: Contributor
timestamp: October 28, 2015, 03:40:47 am
content: I have a table that I keep plugged in all the time that I use to watch netflix/youtube/etc. I can hear, what I assume is, switch-mode interference in my headphones when no sound is playing. Is there some sort of device I can put inline that doesn't require power that will eliminate this noise? Obviously I would prefer if it didnt affect sound quality noticably also.EDIT: I should add, the noise stops when I touch the screen or unplug the power supply. Would it be ground hum? It's a really high pitched whining... definitely higher than 60 hertz, which is why I assume its switch-mode noise.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 28, 2015, 05:39:04 am
content: Not sure about the screen (maybe there's a simple solution, like ferrite beads on the power cable or headphones?), but in general, almost all laptops have awful audio systems, and are rarely quiet when plugged in. Not that that's really helpful..Tim

author: tron9000
author_rank: Frequent Contributor
timestamp: October 28, 2015, 08:56:49 am
content: Quote from: blueskull on October 28, 2015, 03:49:53 amGrim thought!does your tablet have USB port you can use to charge from? if so try a good USB charger that you got with say your mobile phone and see if it goes away? if it goes away, then its the charger, if not then its the tabletQuote from: josephpate on October 28, 2015, 03:40:47 am...I am assuming you mean tablet

author: DrGeoff
author_rank: Frequent Contributor
timestamp: October 28, 2015, 09:04:29 am
content: If it's noise through the USB port then the best solution I've found is to use a pair of audio transformers and isolate the tablet completely.I think there's a Behringer device (HD400) that is pretty cheap and has done the trick to isolate USB audio interfaces connected to laptops from other equipment.

author: josephpate
author_rank: Contributor
timestamp: October 28, 2015, 02:44:22 pm
content: Quote from: tron9000 on October 28, 2015, 08:56:49 amYeah i meant Tablet. It's actually a Microsoft Surface 3 (the non-pro kind), which charges through micro-usb, and I'm using the bundled charger, which SEEMS to be good quality (like the rest of the tablet).Quote from: blueskull on October 28, 2015, 03:49:53 amThese are on-ear headphones with foam pads, not in-ear earbuds.Quote from: DrGeoff on October 28, 2015, 09:04:29 amOoh That's a neat looking device. Even if it doesnt work I'd like to have it in my toolkit anyway. Thanks for the tip.

author: tron9000
author_rank: Frequent Contributor
timestamp: October 28, 2015, 04:48:39 pm
content: I'm really surprised that the bundled charger does that or that the hiccup wasn't discovered during testing/development? its not like its an el'cheapo tablet.

author: josephpate
author_rank: Contributor
timestamp: October 28, 2015, 05:11:00 pm
content: Quote from: tron9000 on October 28, 2015, 04:48:39 pmThat was my thought. So you guys think a differently designed wall charger would fix it? It's not an issue with the design of the tablet itself?

author: tron9000
author_rank: Frequent Contributor
timestamp: October 28, 2015, 05:25:00 pm
content: worth a shot - USB chargers are common now, can but try.

author: Delta
author_rank: Super Contributor
timestamp: October 28, 2015, 06:22:11 pm
content: As has been said, try different USB chargers and see if there's any difference.Try charging it from a laptop with the laptop uplugged (ie just running off its battery), this will confirm if it's switching noise from a mains SMPS or not (although as I'm typing I'm thinking that laptops probably use switching regulators to provide the 5v USB anyway...)Build a nice linear 5v supply!

author: tron9000
author_rank: Frequent Contributor
timestamp: October 29, 2015, 08:32:40 am
content: Quote from: blueskull on October 28, 2015, 07:10:02 pmAhh sorry, you've mis-understood - I meant that this issue wasn't caught. While I didn't know hiccup mode existed, your explanation does ring true.Just I thought that a company like microsoft would be more thorough in testing.

author: josephpate
author_rank: Contributor
timestamp: November 08, 2015, 03:41:54 am
content: Sorry to bump this, but figured it'd be better than making a new post.So I tried A different switch mode USB Wall wart (an Anker device, which is supposed to be pretty well made also) and the switch mode whining still persists. I guess its just poor design on the part of the tablet then?So any more ideas?Quote from: Delta on October 28, 2015, 06:22:11 pmWas this a joke? because I actually went looking for a USB linear supply and couldn't find any.... (that could output 2.1 amps, anyway.)

author: Stonent
author_rank: Super Contributor
timestamp: November 08, 2015, 03:44:11 am
content: Audio Isolation Transformer should take care of it.

author: josephpate
author_rank: Contributor
timestamp: November 08, 2015, 03:48:53 am
content: Quote from: Stonent on November 08, 2015, 03:44:11 amEven if its not a ground loop problem?

author: Stonent
author_rank: Super Contributor
timestamp: November 08, 2015, 03:56:34 am
content: Quote from: josephpate on November 08, 2015, 03:48:53 amHe said that in his experience it removes SMPS noise as well.

author: josephpate
author_rank: Contributor
timestamp: November 08, 2015, 04:00:22 am
content: Quote from: Stonent on November 08, 2015, 03:56:34 amGuess I should've watched it first, heh.

author: Stonent
author_rank: Super Contributor
timestamp: November 08, 2015, 04:07:15 am
content: Quote from: josephpate on November 08, 2015, 04:00:22 amAround 1:30 into the video he talks about SMPS noise.

author: mich41
author_rank: Regular Contributor
timestamp: November 08, 2015, 12:17:21 pm
content: Two sources of noise come to my mind:1. Some battery charging circuit. I'm not sure how these work and can't explain why touching the screen helps.2. CPU switching power states. Disconnecting power cable could help by causing the OS to avoid high power states, using the touchscreen could help by causing it to temporarily stay in high power state to increase UI responsiveness.IOW, experiment with power management settings. IIRC, Windows has some "battery saving" function which disables charging when battery is above 70% full. Try it. Also, try tweaking CPU power/performance settings if there are any. See if loading all CPUs at 100% helps.As for transformers, besides eliminating common-mode noise, their inductance may theoretically kill some noise AM-modulated on an ultrasonic carrier. Maybe that's why they help with SMPS whine, IF they really help.Nevermind, this doesn't make sense with headphones.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 08, 2015, 02:40:46 pm
content: That the tablet outputs low-level digital hash is essentially "normal".Computers (including tablets) are notorious for being poor audio devices.What is surprising to me is that the background noise actually goes away under certain conditions.It is quite common to use isolation transformers when interfacing a computer with an audio system.Especially portable computing devices with "line-lump" SMPS power supplies.Most of us who work in event audio just keep iso transformers in the toolbox.But this is not a "ground loop" situation because the destination gear (the headphones) is not grounded.At least not "hard" grounded.From a description of the symptoms, I would try clipping a ground lead to the case of the tablet.And then see if you can mitigate the symptoms by connecting the ground lead over to building mains safety-ground.You could try connecting through a 1 megOhm resistor or a mains-rated capacitor, etc.