tranformer noise

[audiofan]

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

[tiefbassuebertr]

check out this:
http://www.dalitech.com/Resources/Me...ansformers.pdf
and this:
dc filter

[Guthorst]

Originally Posted by tiefbassuebertr

check out this:
and this:
dc filter

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

[audiofan]

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.

[AndrewT]

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.

[Mooly]

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.

[Bonsai]

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.

[digits]

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.

[audiofan]

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.

[gmphadte]

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