Noisy mains transformer.

[Phil Y]

Hello all,

The mains transformer in my phono stage has always buzzed a little but lately has been getting worse. It is mounted on grommets and I have checked that the bolts through the stack are tight. It seems to be worse when it is cold, it can easily be heard from the listening position. When warm, it is just audible from seated.

Is there anything that can be done, ie potting compound, to quiet it down or is the only solution changing the transformer if I can't tolerate it?

Phil.

[Ali Tait]

You could try swapping the IEC inlet for a DC blocking one, see if that helps.

[Phil Y]

Hello Ali,
I had vaguely heard of this so did a bit of reading up last night and it would appear it only really applies to big toroidals.
Besides, this Tx has always been noisy, it is just that it has got worse. It buzzed when it was sat next to the 2 silent Leak St20s I used to own. I think it is just another victim of modern transformer manufacturing.

Phil.

[Ali Tait]

Another option is to send it to a tranformer manufacurer to have it re-dipped in varnish.

[Phil Y]

Just considering my options, would something like this:
http://www.angela.com/hammondpowertransformer369gx.aspx
be suitable for running a WD phono with EZ80 rectification ?

Phil.

[John Caswell]

Hi Phil,
Which phono stage is it?

John

[Phil Y]

Hello John,
It is a WD Phono 2 audio PCB (with mods from the upgrades section) in the same box as a PSU that is re-used (with mods) from a previous project.

Phil.

[John Caswell]

Hi Phil,
Well why not see if Matthew can come up with a PSU3 Transformer, that is unless you absolutely wish to go the EZ80/90 route. The snag with using the Hammond Tx is that it only has one 6.3V winding so you will need another Tx for the ECC83 heaters. Say a 9V one - bridge rectifier - smoothing - LT1084/LM317 - bit more smoothing. That will give you a nice smooth DC for the heaters, and if you put a pot with limited range on the LM317 you can set 6.3V exactly.
Just in case you ask, not a good idea to run both the EZ80/90 and the ECC83 heaters off of the same winding, just in case the rectifier flashes over.

John

[Phil Y]

Originally Posted by John Caswell

Just in case you ask, not a good idea to run both the EZ80/90 and the ECC83 heaters off of the same winding, just in case the rectifier flashes over.

John

Thanks for that John, well worth knowing.

Using the WD transformer is an option but it would mean rebuilding the power supply so that would be a last resort. If possible, I would rather stay with the current sutup. I will keep looking.
What would you say the minimum HT winding current I should go for, 3 ECC83s can't need much ?

Phil.

[John Caswell]

Hi Phil,
At the most 250-0-250 @ 25mA unless you have a Pre2 with the ECC88 in which case allow an extra 10mA for Zener current etc.
If you cannot get a centre tapped transformer you can always use a hybrid Graetz bridge rectifier which works very well with a 250V single winding, if you want slow warm up or a full bridge SS rectifier if you want instant HT.

John