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Potting transformers

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I have seen many designs that show potted transformers and have often wondered if their is any sonic benefit to doing it or was it just to make a unit appear more pleasing to the wife/girlfriend. In any case can someone go thru the proper procedure for potting one's own transformers? What is used for potting material? Geez this is starting to sound like a gardening post. At any rate... any information will be appreciated as usual.

Thanks
Joe
 
Hello burnedfingers,

Potting the transformer is not hard to do.
If potting the transformer done properly,
it can lower the buzzing noise of the transformer.
But, if you damage the transformer, it will be very hard
or even unpossible to repair it, as the resin will become
rock-solid.

You can use two types of resin for this job.
Polyester and Epoxy.
Polyester is very cheap, and it can have fast setting time.
But, it have smell like in hell, can generate a lot of heat,
and after setting it can shrink a bit.
The more better resin is Epoxy.
It do not smell, setting time is much longer (30 min-24 h),
depending on resin type, and there is no that much shrinkage.
The good epoxy resin is CIBA and LF.

Also you can add some paste color to the resin if you would
like the color it.
Be aware that the some colors can't be mixed with the both
resins, and before you use them, you should check it for which
type of resin it is.

Be carefull, once when you pott the transformer, there is no
way for comeing back, so you should done it properly from the
first time.


Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design-vip
 
RTV potting

Another possibility is RTV potting materials. I came across these when I was looking for thermlly conductive adhesives.

I only have limited experience with RTV, but you will want either heat-cured or 2-part RTVs. One source to check is

www.mgchemicals.com

which are sold by Allied Electronics.

I have only worked with non-flowable RTVs which are not very suitable for potting, but flowable ones exist for this purpose.

At least some RTVs can be removed with a lot of work.

John
 
diyAudio Senior Member
Joined 2002
MIND WHAT YOU DO...

Hi,

Assuming you are all talking about power Xformers,keep in mind that some are running pretty hot and when potted they can short internally.

Nerver pot an OPT unless you really know what you're doing.
If not you risk to alter it's frequency response due to added stray capacitance.

See also:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=6622&highlight=potting

And page three of this link:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=7004&highlight=potting

Ciao,;)
 
Joe,

please avoid potting and potted stuff for potting's sake, makes the trannie expensive and does not gain you anything but a pot looking nice until the lacquer splints off..
Please follow the links Frank gave.
I jut found that Brett bets that i sell my potted Tango after i compared it to the Lundahl.

I don't hold that bet. Wouldn't i be quite optimistic the unpottend but resin-soaked Lundahl outperforms the Tango, i would not order it for tryout, i am pretty short of money. And i have the Tango already.

Now if a potted iron A happens to sound better than an unpotted iron B, that's a reason to keep that particular iron or maybe even swallow the toad of an elevated price.
 
diyAudio Senior Member
Joined 2002
SCREENING,POTTING

Hi,

It wouldn't come as a surprise to that the unpotted Lunddahls would sound more "open" than the potted Tangos.
Even when both frequency plots do not indicate major deviations in the HF response.

Those of you that listened to a screened versus unscreened I/C may have a feel for what I mean here.

Strange but often true.

Ciao,;)
 
My 2 cents... at 20$

Buy some rosin, (5-10$) some isopropilic Alcohol (2$) and a Storage containers vaccum pump (10$)

food storage pump in Food Storage Containers | eBay

1-Put the rosin in the Alcohol and wait until it is perfectly fluid.
2-Put the transformer into the liquid rosin bath and extract all bubbles with the pump
3-Wait...

Your transformer is in beautiful amber matrix resin without any bubble.
 
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I'm a little bit late in the conversation but potting the transformers have very important benefits IF YOU KNOW WHAT YOU ARE DOING. For power transformer the benefit is to significantly reduce and virtually eliminate the hum noise generated both by winding and laminate vibration at 50/60Hz, something desired by the HI-END community. In order to accomplish this properly without sacrificing the integrity of the transformer due to heat transfer, the transformer MUST have a derating temperature higher than the one used in open air, which means potted transformers should be larger to withstand the poorer heat transfer. Of course it all depends on the filling material but as a rule of thumb the transformer shall have +30% increase of the total VA power to offset the thermal issue. The inter-winding capacitances will change but it really doesn't matter for a power transformer. Old stuff was commonly potted with bitumen or some kind of pitch, but it's very messy to do and claimed to be carcinogenic and dangerous for today's environmental regulations. I would prefer the fluid versions of RTV rather than poly or acrilic stuff. Although not so critical, the same rationale is true for the choke if you are using a pi type filter in your power supply, usually adopted in tube amplifiers.

Now, for OPT (tube output transformer or any audio path transformers) I really don't believe the potting adds any benefit other than making the transformer design a nightmare since potting affects the overall capacitances between windings, which may compromise dynamic behavior and response bandwidth, since the annoying "hum" should be already addressed by the power transformer/ power supply.

Make your choice and "be happy" !

---------------------------------------------
Claudio Baldoni Jr. Electronic Technician since 1979; Electronic Engineer since 1984; Audio enthusiast since when I was a kid....
 
Member
Joined 2015
Paid Member
Some vintage transformers are potted with vax. It is then possible to remove the transformer from the can with ease, for inspections and repair. Could wax still be a good solution today?
As drawback, the wax will spill out on the chassis if the transformer is overheating, this is a pretty common sight on old amplifiers with this kind of potting material.
 
Wax was used in the past due to the lack of better alternative I may say, for the reasons I mentioned before about the use of bituminous stuff ... Wax melting point is too low for a power or OPT transformer that will be hot for sure. It may improve the overall insulation (just like oil) but it is not going to address the hum noise as the wax will melt again around the wires while hot, which may allow the wires to vibrate anyway. For an audio application, either the melting point is high enough to keep it solid on transformer's running temperature, or you should use something that once cured it becomes solid (like poly and acrilic) or semi-solid (RTV). Needless to say none of them (RTV maybe) will allow you to dissamble or repair it properly.
 
Sorry to resurrect this but I've read through the posts and couldn't find an answer to these questions... Lets say I wanted to try my hand at potting a choke (just for the experience of doing it, not if I should or not).

Seems obvious but just checking here... If the choke I'm potting has end bells I'd have to remove those first correct? So the open coil is actually in contact with the resin.

I have several transformer covers, the deep-drawn steel press-fabricated kind, seamless. I'm assuming this is the typical type of "can" one would use to enclose the whole thing? Is aluminum better than steel for the potting can, for a choke? In placing the choke into the can I suppose I should first harden a half inch of resin in the can, so when I set the choke into the can for the final pour it is not in direct contact with the can? It would be sitting on half inch of resin, then do the final pour, slowly with vibration.

Hammond potted versions of the same choke model are literally more than double the price. I've used epoxy and fiberglass resins for many other projects in my life so that part is second nature, made boats, etc. I'm only talking chokes.
 
If you pull the covers off of a filter choke, there's some risk that you'll disturb the air gap.

If you put the choke in the can with the holes facing up where the wires poke through, you can pour resin right into those holes first to be sure the resin gets in there.

See that's why I ask! Thanks. My instinct would have been to pull the covers, but I'll leave them on and just fill the cover cavity via the holes, makes sense, extra shielding too and I wont disturb the construction. I've used thin resins that will definitely flow well into the bells as long as I have an entry hole. Using a disposable resin syringe and go slow. I will still pre-pour and let a half inch of resin to set first in the top of the can, so the choke never contacts the upside-down can, two pours.
 
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