UK- what cheap things can I buy that have bagel shaped transformers that whine?

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I'm in the UK. What cheap things can I buy that have bagel shaped
transformers that whine?

The reason, is I want to practice silencing them, with liquid epoxy.

These are the kind of transformers i'm talking about
http://linitx.com/index.php?cPath24%_55

http://img81.imageshack.us/img81/7159/carpsu90wframelargelo9.jpg

But I want to practice on something cheap.


Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?
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Are you sure its just the torroids/coils that are whining ?
Copal varnish was the norm for laminated iron cores that rattled, it is less
rigid than epoxy which may be relevant


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
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Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?



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What exactly are you up to ?

Whining may indicate poor design, inferior materials or sloppy construction
here.

Graham



Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?

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Or a fault. The image shows torroidal chokes, not transformers, and it's
fairly rare for them to whine anyway, unless there is a problem. These items
can actually run quite hot in normal use, so anything used to quiet them
needs to take this into account. As Graham says, what exactly are you
looking to do here ? I could suggest any number of cheapo switch mode power
supplies that utilise these chokes, but you could buy a hundred, and not get
one that needs attention for whining. Maplin sell the actual chokes - or at
least they did when I last bought some - so it might be worth just buying
some, and then seeing if you can persuade them to rattle by hitting them
with some high level audio from a signal generator, or dare I suggest, from
an amplifier, but with the caveat that you would need to be careful not to
load the amp too hard with the unknown impedance that you would be
presenting to it with one of these chokes. Once you've found a mechanical
resonance frequency where you can get the windings whistling, you can
experiment away. I would have thought that one of the liquid silicone rubber
coatings may be more effective at quietning a torroidal choke.

Arfa



Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?
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people have aksed me

what am i up to
am I sure it's the coils
are these "torroidal chokes" or transformers
I have to take  into account the heat these things produce..
why not get ac dc adaptors  ..


Well.. I want a fanless computer, it's an ideal, but i'd like it. And
I don't like things that make a high pitched whining noise either.
Some years ago the only option was a VIA machine. Now, there are
fanless components, but i'm not convinced how long a regular MBRD
would last fanless. There are "voltage regulators" on the mbrd that
need cooling, i'd need a heatsink for them. And i'm not sure how
reliable the fanless power uspplies are.

A VIA system is cheap.  I built one years ago anyway.  But there was
one problem.

The Fanless power supply card made a high pitched noise. Just like
some TVs do. Just like some cheap ACDC adaptors do. That power supply
card was made by a company called Morex. There was another competitor
that made one but it had the same problem.  I contacted Morex, and
they said it was because the transformers were not made with ferrite.
And to do so would be more expensive and they don't do it.

I have no electronics background. But getting some liquid epoxy and
filling up a bagel shaped transformer, or thing that looks like a
transformer. That I understand! Epoxy I think conducts heat.

The morex power supply card (I bought it from linitx),  has gone
walkies, and the newer versions are probably not the same. THey may
whine, they may not whine.  Most shops they can't hear the whine. If
they could then they I doubt they'd be able to use it!!

I did buy a cheap AC-DC adaptor and it whined, so I took the
opportunity to try to silence it. That didn't work out.
See the transformer second from the left second row from the back.
http://img135.imageshack.us/img135/3100/transformercoilsinductooq8.jpg
That's what it had.  So, I couldn't get liquid epoxy into it if I
tried.
I tried unsoldering it but it wasn't coming out unless I snapped the
board.

So I resigned my hope to merely being able to silence bagel shaped
transformers.  Ones that I can get to.

I remember my old morex power supply card had them.

It'd be nice if I had some unviersal way to silence those. e.g. liquid
epoxy. I need some cheap way of trying it.

As mentioned, the ACDC adaptor thing didn't work out. It whined but
was in a housing.

I'm sure in the case of the morex power supply card , it was the
transformer that was whining. I managed to bare the nightmare of
putting my ear near it to find the culprit.  The morex technicians
thought it was the transformers too, and admitted they whine!







Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?
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   ??? Use a piece of 1/8" or larger plastic or rubber tubing.  Stick
one end in your ear and use the other end to identify the noise source.
Automotive vacuum or windshield washer tubing are cheap, easy to find,
and is sold by the foot.



--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
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Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?

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Some of those items in the picture are transformers, some are chokes. The
one that you point out looks like a tranny, but that's by the by now that we
know what you are doing, anyway. I think that the only way you are going to
stop rigid ferrite cores from rattling at their drive frequency, is to
muffle them with something soft, which may or may not affect the temperature
that they run at, depending on whether that's hot in the first place.

There are liquid - or at least semi-liquid - silicone rubber compounds
available, with non corrosive properties, designed for 'soft potting' of
electronic sub assemblies. I used to use one made by Dow Corning for
encapsulating a counter board that had to work in very hostile and moist
conditions. You could try surrounding any offending transformers with a
little cardboard 'wall', and then filling this with the rubber compound. I
don't think that much whine would escape that, but you might still be
contending with vibrations transmitted directly into the PCB via the core
touching the board, or even via the pins. Go have a look at

http://uk.farnell.com/jsp/search/results.jsp?N41%1&Ntk=gensearch_001&Ntt=silicone+rubber&Ntx =

where there are lots of them with pdf data sheets

Arfa



Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?
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ok.. i'll try some of those - what look like liquid compounds  - at
your link. And i'll try the liquid epoxy too.

But where will I find a cheap product with bagel shaped whining
transformers  or chokes..

I don't have an electronics background. Is it feasible for me to buy
them separately, connect a battery to them and get them running so I
can try.. ?

Is there any place where I could get instruction on how or any book or
website with an example ?

I'd even consider paying an electrician geek in the UK, as long as
it's not too many hours. If they've got the expertise. Though i'd like
to know how to do it myself.  If I could ask an electronics geek and
as part of that, learn how to do it myself that'd be ideal..







Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?

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Well, as I said, Maplin stores sell those toroidal chokes for constructors
who want to put together their own chip-based switching power supplies.

http://www.maplin.co.uk/Search.aspx?criteria=torroidal%20chokes&source15%&SD=Y

If you have an old hifi or amplifier kicking about, you could connect one of
these across the output, and hit it with some music - I guess that violin or
piano might be good. But I would caution you to start with the volume right
down, and only wind it up enough to get the choke singing with the music,
because it will represent an unknown impedance. Any decent amp would protect
itself against any damage that might ensue if the impedance happened to be
very low, but obviously, I can't guarantee that,

Another source for those chokes would be your local computer repair shop, or
a TV repair shop if you have one around you. Either of those will have scrap
switch mode power supplies coming out of their ears, which I'm sure they
would be happy for you to relieve them of. You will find plenty of coils and
chokes on those that you can remove to experiment with.

Arfa



Re: UK- what cheap things can I buy that have bagel shaped transformers that whine?
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i'm more of a computer techie than electronics geek.  I see from the
picture at the link, the "choke" has 2 metal wires coming from it.

Now, if I want to connect that to a piano or a violin.

It sounds like I don't need to connect a battery to it. I thought I
would have had to!

Would I be touching both prongs against violin strings?

I notice a piano has metal rods in it that vibrate. I guess the same
thing applies.


The chokes or transformers make their unbearable high pitched noise
(so very high frequencies). I can't imagine that somehow connecting a
piano or violin to it would get it at that high pitched unbearable
noise which I recognise and want to silence.   I'd have to trust in
the assumption that if I can get the choke or transformer  singing at
all,  and then silence it, then it's silenced at any frequency,
including that unbearable one.   Is that a fair assumption? Maybe an
"amplifer" would let me choose frequencies including that unbearable
one. Would it have rods to touch the prongs of the choke against?

my other concern is that those rods on the piano look like they might
be quite delicate. I wouldn't want to mess up the piano's sound. Or
drop a choke in the piano! Similarly, I haven't seen people with
violins plucking strings with their fingers, they sort of stroke the
strings with a rod, so, those strings may be very delicate too. I'm
wondering about the amplifier option. Is there a cheap amplifier that
can reach the unbearable frequency, and does it have rods?!!

(the unbearable frequency must be related to AC, so it's probably a
frequency known to electronics geeks, you prob know it)

thanks
















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