Topic 'Re: random hiss from speaker - capacitor?' in forum 'Electronics' - dslreports.com

Re: random hiss from speaker - capacitor?

Sat, 22 Sep 2012 09:04:23 EDT

AndrewG2 posted : Well said... it would of course be desirable to see round the side of it. But I've seen plenty that catch a mechanical nick like that on top, even "brand new" and some where the heatshrink had an imperfection like that (i.e. didn't shrink quite right). So on available information, even though I've also seen plenty of bulged, leaking and damaged caps also, I'd put down my 2c on that side of the equation.

Re: random hiss from speaker - capacitor?

Fri, 21 Sep 2012 22:27:14 EDT

SmokChsr posted :

said by AndrewG2:

looks like nothing to me, unless your eyes are fooled by the diagonal cap behind it.

While the picture is from the wrong angle to confirm anything, anytime the shrink wrapping is pealing off an electrolytic, it definitely demands a close examination.

Only if the wrap was damaged by non-deforming (to the metal shell) mechanical damage from external forces would it not be much of a concern. Other wise anything that would damage the wrap, either from inside or outside the cap would indicate that the cap was highly suspect.

Re: random hiss from speaker - capacitor?

Thu, 20 Sep 2012 15:19:05 EDT

AndrewG2 posted : I see dust.

Re: random hiss from speaker - capacitor?

Thu, 20 Sep 2012 15:16:04 EDT

iknow posted :

said by AndrewG2:

Oh no, a nick in the heatshrink, containment is breached, she's going to take out the whole of Metropolis!!!

i.e. looks like nothing to me, unless your eyes are fooled by the diagonal cap behind it.

the case of the capacitor split open, that's why the heatshrink is split and coming off, you can see some of the electrolyte sprayed onto the cap next to it.

Re: random hiss from speaker - capacitor?

Thu, 20 Sep 2012 13:51:31 EDT

AndrewG2 posted : Oh no, a nick in the heatshrink, containment is breached, she's going to take out the whole of Metropolis!!!

i.e. looks like nothing to me, unless your eyes are fooled by the diagonal cap behind it.

Re: random hiss from speaker - capacitor?

Thu, 20 Sep 2012 11:50:26 EDT

iknow posted :

said by AndrewG2:

How random is the random hiss, does it turn on constantly for 15 mins or more, or is it more like psssssssssssst stop psssssssssssssst etc with random length bursts and pauses over a few minutes?

If it's the second scenario, I suspect it's RF breakthrough from taxis, police or utilities radios where the carrier is breaking through, but modulation is not strong enough to hear any "signal". i.e. distant signals a mile or so off.... however, if a cab stopped right outside his house to check in, it might bleed through audio, (and blast him out of bed at 3AM if he left it on and turned up :D )

The capacitor at the bottom of the red line has it's wrapper coming off.

Re: random hiss from speaker - capacitor?

Thu, 20 Sep 2012 07:12:58 EDT

AndrewG2 posted : How random is the random hiss, does it turn on constantly for 15 mins or more, or is it more like psssssssssssst stop psssssssssssssst etc with random length bursts and pauses over a few minutes?

If it's the second scenario, I suspect it's RF breakthrough from taxis, police or utilities radios where the carrier is breaking through, but modulation is not strong enough to hear any "signal". i.e. distant signals a mile or so off.... however, if a cab stopped right outside his house to check in, it might bleed through audio, (and blast him out of bed at 3AM if he left it on and turned up :D )

Re: random hiss from speaker - capacitor?

Tue, 14 Aug 2012 02:31:53 EDT

SmokChsr posted : Also lets not forget those resistors, if they are getting that hot, it's very likely that the solider joints have become crystallized and fractured, which is a very likely source of noise.

Re: random hiss from speaker - capacitor?

Mon, 13 Aug 2012 21:44:00 EDT

UHF posted :

said by SmokChsr:

Yep, I missed that one. Being an electrolytic, it could be a source or the trouble.

That was my first thought too. Lately I've had a lot of bad electrolytics causing me problems.

Re: random hiss from speaker - capacitor?

Mon, 13 Aug 2012 19:50:17 EDT

SmokChsr posted : Yep, I missed that one. Being an electrolytic, it could be a source or the trouble. Either way if it did get hot enough to melt the plastic, it likely got hot enough to do further damage. Unlike the ceramic electrolytics are heat sensitive.

Re: random hiss from speaker - capacitor?

Mon, 13 Aug 2012 18:13:28 EDT

iknow posted : no one noticed the cap at the bottom of the red line with it's wrapper coming off? it looks like it overheated!.

Re: random hiss from speaker - capacitor?

Sat, 11 Aug 2012 00:16:37 EDT

SmokChsr posted : I'm not likely to suspect the Cap either. The resistors did the scorching. Those ceramics typically don't care. For a noise like that you'll likely have to get an idea of the signal path and try to follow it back. Typically this comes from a bad amp module, if that's what it has.

Re: random hiss from speaker - capacitor?

Tue, 07 Aug 2012 10:56:15 EDT

amungus posted : That's what I thought too. That those little ceramic guys were pretty solid. Worth asking though, since that's the only visibly bad area of the board.

Might check for cold solder, wouldn't surprise me at all...

As for channels - yes, since the sub contains the amp circuitry, it seems to send a little hiss to L/R channels.

Re: random hiss from speaker - capacitor?

Mon, 06 Aug 2012 18:27:06 EDT

Tursiops_G posted : Ceramic caps usually don't go 'intermittent'... Just for grins, I'd take a closer look at those power resistor's leads for 'cold' solder connections on the board, and 're-wet' them with fresh solder if needed... ;)

-Tursiops_G.
--
If You're Unsure, "RTFM"... If You're SURE, "RTFM" Anyway. ;)

Re: random hiss from speaker - capacitor?

Mon, 06 Aug 2012 13:46:06 EDT

SparkChaser posted : Do both channels do it?

Can you move it to another location and still get it?

Is the cap really scorched? I haven't seen that much in low voltage equip.

Could be a cap or transistor.

What ever happened to signal tracers? :D
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Re: random hiss from speaker - capacitor?

Mon, 06 Aug 2012 11:40:58 EDT

amungus posted : Thinking it was the proximity of the two resistors - they were both touching, so I gently gave some 'breathing room' there.

There is a 3G tablet (and sometimes cell phone) nearby most times, but the amp is in the sub, which is on the floor - about 2-3' of distance b/w devices and the amp. Unlikely to interfere, but not a bad thought, and certainly a possibility. We could try having those moved slightly.

Re: random hiss from speaker - capacitor?

Mon, 06 Aug 2012 11:06:40 EDT

DrStrange posted : 1. What caused the cap to scorch? Might be a symptom of a larger issue.

2. Is there a cell phone anywhere the speaker [or the amp or the wiring] when it randomly hisses?

random hiss from speaker - capacitor?

Mon, 06 Aug 2012 10:54:02 EDT

amungus posted : Working on a friend's m-audio LX4 2.1 powered speakers.
Very randomly, it has a small 'hiss' sound, even without input.

Took it apart and found one little ceramic cap that seems a little scorched. Should I bother replacing this little guy (digikey?), or investigate further?

The resistors shown were really really bunched up against the little capacitor, and as you can see, so I moved them just slightly out of the way... there's even a little bit of a heated spot on the edge of the board.

For reference, the two pins near the circled spot are the output for the subwoofer speaker. I believe this to be the

Kind of a strange issue - the speakers still sound good, it's just that there's a very random hiss that cropped up recently. Could be anything really (passing UFO?), but I thought I'd start with checking components.

Thoughts?