May I dip a power transformer in orange shellac to glue everything in place and ge rid of the hum noise.
Is dielectric constant of orange shellac close to the usual varnish used in power ransformer industry. ( secondhand transformer from a HP PROPRINTER )
In my case they are standard steel laminated standard E & I core
Is dielectric constant of orange shellac close to the usual varnish used in power ransformer industry. ( secondhand transformer from a HP PROPRINTER )
In my case they are standard steel laminated standard E & I core
This thread seems to focus only on DC at the primary transformer winding. But it must be considered that also DC drawn from transformer's secondary results in singing toroids. One-way rectification will result in direct current and that will result in hum, even if it is only used for low power auxiliary supply.
Guthorst
I will check for dc component in mains , I may also test with an isolation transformer and get rid of any DC component and any ground loops.
These transformer are use to power Leach Amplifieir, if there is an unbalance in secondary winding and DC through secondary it must be a very low value.
These transformer are use to power Leach Amplifieir, if there is an unbalance in secondary winding and DC through secondary it must be a very low value.
Using a bridge rectifier virtually ensures equal loading on the two halves of the output windings.
You don't need to concern your self with induced DC due to unequal loadings until you deliberately draw unmatched current in the to & fro directions.
You don't need to concern your self with induced DC due to unequal loadings until you deliberately draw unmatched current in the to & fro directions.
This explains it quite well...
Mains DC and Transformers
As to dipping in varnish... that doesn't always have the desired effect although that said I have done that many times when I was a bench tech working with cheap equipment.
Mains DC and Transformers
As to dipping in varnish... that doesn't always have the desired effect although that said I have done that many times when I was a bench tech working with cheap equipment.
The first thing you need to do is decide if the noise is because there is DC on the mains, or, whether your problem is infact just loose windings and/or loose laminations. in the case of the latter, dipping the transformer in varnish of lacquer will certainly help. if its DC on the mains, you need an entirely different approach. See Rod Elliot's site for a good technique to remove DC from the mains.
Often a simple filter like a 220nf x2 capacitor in series with a 10W, 1 ohm resistor from live to neutral, placed before the transformer will clear the hum up alot.
I made a test tonight with an isolation transformer, since you cannot get DC from a transformer there was no DC in primary.
But the transformer noise did not change at all.
But the transformer noise did not change at all.
U have to shield the transformer i.e. enclose the transformer in mu metal or copper. Even iron will do as most commercial audio does the same.
Gajanan Phadte
Gajanan Phadte
Have you looked at the secondary outputs on a scope ?
That will show if the mains is "pure". Is the transformer noisy with nothing connected on the secondaries ?
That will show if the mains is "pure". Is the transformer noisy with nothing connected on the secondaries ?
Will an isolation transformer pass through the non equal halfwaves that can be present on the mains supply?
There is no electronic hum I have lamination vibrations and mechanical noise...
I will have to dip the transformer in some kind of varnish. But will orange shellac work over standard varnish ....
There is a fire hasard with this repair if dielectric constant of shelleac is too high then the electrical varnish may have a breakdown, and spark through the varnish will set fire.
I will have to dip the transformer in some kind of varnish. But will orange shellac work over standard varnish ....
There is a fire hasard with this repair if dielectric constant of shelleac is too high then the electrical varnish may have a breakdown, and spark through the varnish will set fire.
Heat the varnish before you dip the transformer. The air inside the transformer expands and escapes as bubbles that rise to the surface.
Cool the container fairly quickly. The cooled core now has cooled air in the laminations and this sucks in the varnish. Reheat the varnish and more of the trapped air will be expelled. Now let the transformer and varnish cool right down. Take out the transformer and let the varnish set. Probably a couple of days (or more) for the volatiles to escape from the core.
Cool the container fairly quickly. The cooled core now has cooled air in the laminations and this sucks in the varnish. Reheat the varnish and more of the trapped air will be expelled. Now let the transformer and varnish cool right down. Take out the transformer and let the varnish set. Probably a couple of days (or more) for the volatiles to escape from the core.
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Only you can determine what is happening... any impurity on the mains makes itself heard as noise in the transformer.
Can't see any risk as the transformer and windings are already fully insulated. As long as whatever you use doesn't attack the original varnish it should be fine.
Is it worth all this effort on a s/h tranny ?
if it's a loose winding dipping (soaking is more accurate, since you want it to soak in far enough to cover the loose winding) in varnish should help, and don't test it until the varnish is completely dry inside the transformer.
about varnish mix
If the varnish I use is too defferent from the original ( dielectric constant ) the result may be catastrophic. Electric field betwen wires will change it may be as catstrophic as pouring water.
If I use a varnish with a dielectric constant similar to the varnis already used electric fielsand stress will spread envenly.
If the mew varnish have a very high dielectric constant the electric field will be lower in the new varnish and will concentrate in the old one, and it may let to a breakdown of the insulation.
a comparaison can be made with a mechanical device using several springs, if you change a spring for a steel link the remaining spring will have to expand more ant it may break the remainig spring.
I the transformer a part of the electrical stress is spread in the air trapped inside. if I inject a new varnish with a very high dielectric constant the field will be disturb.
If the varnish I use is too defferent from the original ( dielectric constant ) the result may be catastrophic. Electric field betwen wires will change it may be as catstrophic as pouring water.
If I use a varnish with a dielectric constant similar to the varnis already used electric fielsand stress will spread envenly.
If the mew varnish have a very high dielectric constant the electric field will be lower in the new varnish and will concentrate in the old one, and it may let to a breakdown of the insulation.
a comparaison can be made with a mechanical device using several springs, if you change a spring for a steel link the remaining spring will have to expand more ant it may break the remainig spring.
I the transformer a part of the electrical stress is spread in the air trapped inside. if I inject a new varnish with a very high dielectric constant the field will be disturb.
Never had any failures or issues dipping wound components.
Done it on everything thing from mains transformers, SMPS trannys, coils and ferrites, line output transformers (TV with EHT), scan coils etc etc.
Done it on everything thing from mains transformers, SMPS trannys, coils and ferrites, line output transformers (TV with EHT), scan coils etc etc.
Don't even think of using shellac, It breaks down at low temperatures and has poor (nil) mechanical qualities. Varnish is a type of polyester resin and once the solvent is dried out and the resin air cured, it becomes a tough, crosslinked polymer, good for 130C using approved types.
There is no easy way to do this at home. If you believe you will stop buzzing this way, expelling flammable and toxic solvents is part of the process. I would suggest however, not to heat the varnish - just the transformer to around 65C. Fit lifting wires and place in a close fitting can and quickly pour in varnish and cover fully.
Allow it all to cool significantly and then lift to drain the varnish, air-dry for several days and continue drying while increasing temp. to cure the varnish without simply forcing it back out. Difficult? yes but if you want to be effective with a power transformer, it wont be fixed with a little splash of paint, that's for sure.
The principle is simple. The varnish cools the transformer and the air in it contracts, drawing in the varnish and simultaneously heating it, thus reducing viscosity. (Neater and safer this way)
Understand that trying this indoors is crazy 😱! - work outdoors to avoid being overcome by hot vapour, and accidents. Varnish solvent (Xylene) has a variable flash point around 80C - do not heat to or use a stove that reaches this temperature and could possibly ignite the vapour with a spark, incandescent element, flame etc.
Industrially, high vacuum is applied, then released to allow atmospheric pressure and more, to do a thorough job of impregnation.
Electronic fix
Recent work with buzzing toroids in new 20W class A amp. kits here, has seen great improvement with choke/capactor filtering. It's subject to copyright, but for a 2 x 22V AC @ 2.5A constant load, a 470uH powdered iron toroid in each rail immediately following the bridge rectifier, worked wonders. There is also an 0R02 resistor in each secondary lead of the transformer C.T.- simple additions reducing mechanical noise from slight distraction to unnoticeable in this application.
Like any power inductance, keep the 5A rated chokes well away from the amplifier inputs. (Ref. Silicon Chip magazine - April 2011)
http://www.siliconchip.com.au/cms/A_112410/article.html
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also an interesting step to reduce the mechanical hum of a toroidal
more URLs to this amp:
Altronics - Your One Stop Audio Visual & Electronics Supplier
http://forums.overclockers.com.au/showthread.php?t=639510
http://www.diyaudio.com/forums/soli...icon-chip-20w-class-amplifier-opinions-2.html
PS
about
http://www.diyaudio.com/forums/soli...oidals-summary-most-interesting-comments.html
I have create an overview from the most interesting comments arround DC filter against mechanical hum.
more URLs to this amp:
Altronics - Your One Stop Audio Visual & Electronics Supplier
http://forums.overclockers.com.au/showthread.php?t=639510
http://www.diyaudio.com/forums/soli...icon-chip-20w-class-amplifier-opinions-2.html
PS
about
http://www.diyaudio.com/forums/soli...oidals-summary-most-interesting-comments.html
I have create an overview from the most interesting comments arround DC filter against mechanical hum.
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