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Old 02-14-2021, 04:03 PM   #1
Jumme
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Default Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

So. Had my Boston Acoustics subwoofer for 4 years and it had a terrible coil whine squeal from day one.

I RMA'd it twice, but both times it came back (after a 6-8 weeks return time) and had the exact same problem.
Said they "swapped the amplifier module". As it didnt help, personally I feel more convinced its the PSU module. Company now bankrupt and I cant stand the noise:

Its a high pitch coil whine tone -it's terrible agonizing, when worst, I hear it clearly 4-5 m from the Sub (because sits in corner).

It wines without RCA input. It whines in both active mode and stand by (inactive) mode, though changes a bit in frequency and often gets noticeably higher when in stand by!

It whines if I move it to a completely different room/power source. Whine makes a weird "squeak squeak squeaaiik" and then dies, when power is pulled.

I opened the sub, not being able to exactly pin point the source. I also didnt see any bulged caps, everything looks normal and smells new.

Fun fact; Im pretty sure the sound dropped dramatically for a period when sub was upside down, being opened up.

I have basic knowledge and repair skills like changing dead caps.


Question is: Will I be fine with "drowning" the coils (I see at least 2) with eg. hot glue as a start?
Or what to do? Thanks!!

Diagram (Im pretty sure. Or very similar).

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Old 02-14-2021, 05:45 PM   #2
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

it's a coil or ceramic capacitor i suspect.
if you take a plastic rod - like a bic pen, and prod any coils or big ceramic disk caps you should find the cause.

if it's a coil you can use the old russian trick of coating it in wax,
or you could smear epoxy or silicone on it.
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Old 02-14-2021, 05:48 PM   #3
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

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it's a coil or ceramic capacitor i suspect.
if you take a plastic rod - like a bic pen, and prod any coils or big ceramic disk caps you should find the cause.

if it's a coil you can use the old russian trick of coating it in wax,
or you could smear epoxy or silicone on it.
Thanks a lot, much appreciated. 'Prod any coils', how exactly?

Sorry, English is not my first language.
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Old 02-14-2021, 07:14 PM   #4
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

Just poke/touch them with the insulated stick and see if the sound changes / stops when you press on it (gently).

The noise is caused by the coil or other component vibrating at an audible frequency. If you poke it with a stick, it should dampen the vibrations and thus change/stop the noise.
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Old 02-15-2021, 05:27 AM   #5
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

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Just poke/touch them with the insulated stick and see if the sound changes / stops when you press on it (gently).

The noise is caused by the coil or other component vibrating at an audible frequency. If you poke it with a stick, it should dampen the vibrations and thus change/stop the noise.
Thanks, that makes good sense!

Q: I read somewhere a long time ago that noise could be due to design fault; not being induced from the noisy component itself but rather somewhere else in the circuit. Thus tampering whit the component would not help, but changing eg a diode somewhere else would. Whats your opinion on this?

Is that explanation only related to speaker humm (which my problem is definitely not)?
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Old 02-15-2021, 06:26 AM   #6
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

without a schematic you cant really get into design aspects.
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Old 02-15-2021, 10:19 AM   #7
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

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without a schematic you cant really get into design aspects.
I understand.

The culprit is the coil wrapped in yellow paper or tape.
This is to already reduce noise, correct? Its also covered in some guey but hard compound, I think that's called conformal coating. Even so its making an audible squeaky whine.

Im pretty sure this is 230V in, and also the board that relays the sub in standby mode after a few minutes with no input. I have a suspicion whine is getting higher under load/after some time/warm, and worst when the unit then goes into stand by mode.

When I press point A the sound wanishes or at least lowers a lot. When I press or poke points B the sound changes a bit but not as much as point A.

Would it be enough to cover the ferrit with nail polish?

I don't really have any RTV silikone or conformal coating. Just regular house hold stuff.
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Old 02-15-2021, 12:51 PM   #8
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

oh, a transformer.
it could be the ferite frame vibrating against the plastic inner part.
do you have any discount stores near you?
the type that sells all kinds of shit for a € ??
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Old 02-15-2021, 01:51 PM   #9
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

Phenolic/SRPB circuit board?
Awful tan glue on everything?

I think the power supply is a victim of "cost optimisation"

Could be noisy from cheaply made & loose transformer, or a cheap circuit design that runs noisy anyway (?) But as mentioned, you'd need a schematic to begin trying to figure that out.

I'd go with putting some kind of epoxy etc in the transformer to hopefully stop it vibrating - I'm sure stj has some good ideas about that.

I'd personally also get rid of all that factory glue if you want the thing to last any appreciable time. (It goes corrosive/conductive over time and destroys electronics, God knows why they still use it. Oh right, planned obsolescence.)
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Old 02-15-2021, 02:14 PM   #10
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

Quote:
Originally Posted by stj View Post
oh, a transformer.
it could be the ferite frame vibrating against the plastic inner part.
do you have any discount stores near you?
the type that sells all kinds of shit for a € ??
That depends on if you have something specific in mind??

I live in Denmark. Nothin is cheap here, not even in the cheap shops..

Quote:
Originally Posted by Agent24 View Post
Phenolic/SRPB circuit board?
Awful tan glue on everything?

I think the power supply is a victim of "cost optimisation"

Could be noisy from cheaply made & loose transformer, or a cheap circuit design that runs noisy anyway (?) But as mentioned, you'd need a schematic to begin trying to figure that out.

I'd go with putting some kind of epoxy etc in the transformer to hopefully stop it vibrating - I'm sure stj has some good ideas about that.
I think you're right, and that's exactly what Im hoping to do.

Quote:
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I'd personally also get rid of all that factory glue if you want the thing to last any appreciable time. (It goes corrosive/conductive over time and destroys electronics, God knows why they still use it. Oh right, planned obsolescence.)
I'm not gonna spend a minute more than necessary, not knowing what Im doing. Im lucky if the unit survives this repair attempt.
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Old 02-15-2021, 02:19 PM   #11
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

The ferrite on that transformer is not aligned well, that might be the issue.
But I would be really careful about realigning it as it could crack, and then it is game over.
Easiest might be to try to poke something under it, like a straw (sugrör) maybe that could work?
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Old 02-15-2021, 02:22 PM   #12
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

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Easiest might be to try to poke something under it, like a straw (sugrör) maybe that could work?
You mean, completely under the transformer? Between component and board?
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Old 02-15-2021, 02:49 PM   #13
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

Yup, if there is enough room to squeeze it under...
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Old 02-17-2021, 08:05 AM   #14
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

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Yup, if there is enough room to squeeze it under...
Thanks for your kind reply. There wasn't enough space around the transformer to get a straw in, so I choose another route:

I took some red varnish made specifically for coloring light bulbs, and gave the transformer a thick coating. After letting it drip and harden 24 hours, I also covered the transformer and the whole area in hot glue.

(SO FAR) the high pitched squeaking is completely gone and I am VERY happy!

Though it was probably not the correct coating solution, Its my opinion that you sometimes have to work with what ever you've got at hand. Thanks for all the help.
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Old 02-17-2021, 12:59 PM   #15
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

Great! The varnish should be all you need though, so you probably don't need the hot glue, and in fact it may be better not to have too much stuff covering everything, otherwise things could overheat.
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Old 02-17-2021, 01:40 PM   #16
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

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Great! The varnish should be all you need though, so you probably don't need the hot glue, and in fact it may be better not to have too much stuff covering everything, otherwise things could overheat.
I celebrated too soon. After only 6 hours of use the squeaky tone is back. Less than before but still noticeable.

Im probably gonna swap the unit for another 2. hand sub, but the repair was worth a shot.
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Old 02-17-2021, 02:03 PM   #17
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Default Re: Boston Acoustics Soundware 5.1 SUB: Agonizing coil whine!

I wonder if the varnish/glue melted from heat and loosened up.

Can you try something that has a higher melting point than hot glue?

Perhaps desolder the transformer and dip it in a high temperature varnish or epoxy.

https://groupdiy.com/index.php?topic=70265.0 is interesting...

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