Replacement of a Humming Transformer in a Beomaster 4000 with a Modern Toroid

Hi All,

I thought this would be interesting to owners of humming Beomaster 4000/3000s:

I designed a solution to replace the original rectangular transformers with a modern custom manufactured toroid and a 3D printed mounting bracket that fits the original bolt holes of the transformer cabinet. It maintains full functionality of the input voltage selector due to a 1:1 match of the original primary winding scheme and also features an integrated thermal switch. Details can be found on my blog: http://beolover.blogspot.com/2016/03/beomaster-4000-2406-installation-of-toroid-transformer.html

An impression of the inserted toroid with its mounting bracket:

That is excellent! I know there are quite a few Beomaster 4000 units out there with the transformer vibration/hum problem. This is a nice clean fix.

-sonavor

Very nice. As always.
I attempted the same once but gave up when I found out how much noise was radiating from the transformer into both the rectifier
and the nearby volume (loudness board). Probably why the original transformer is shielded.
Toroids don't like metal shielding - they typically see it as a heavy load (a "magnetic short") so will run very warm.
How did you solve this ?

Martin

Excellent points! I was very worried about EMI when I set out to build this and I had a long discussion with the experts at toroid.com. They are a really friendly bunch and very open to noob questions. I can only recommend working with them. It was a great experience.

It appears that toroids are the preferred solution for noise-sensitive equipment since their magnetic field is confined to their core (in difference to standard "EI" transformers where the field lines can escape by design-hence the shielding can of the original transformer). Most modern high-end audio components seem to use toroids in their power supplies. Also the Beomaster 8000 and the 6000 4-channel are equipped with toroids. The one in the 8000 is in a metal can, while the 6000's is unshielded.

In an ideal toroid there is no magnetic field on the outside. Due to the geometry everything cancels out. But of course in a real world implementation some flux escapes. One issue is that one has to go in and out with the wires, creating a 'hole' in the 'infinite coil', and then there are winding imperfections etc...

Since I seemed 'concerned' they suggested the installation of a "magnetic shield" (it is that black band around the toroid in my pictures), but they said that this is not really necessary for audio applications. My tests so far yielded that there is no noticeable 60Hz noise in the Beomaster 4000 inputs but I will scrutinize that a bit further down the road.

Rudy

Well, it did cause problems here - lots - but maybe that was just a bad transformer ().
The magnetic shield metal is perhaps mu-metal, it's also used inside computer harddisks to prevent the heavy magnetic
fields from the voicecoils reaching the delicate magnetic data disc media.

Anyways, if it still works troublefree also with the Beomaster bottom plate fitted I'd call it an excellent solution.
Was the toroid custom wound?

Martin

Beolover:

Excellent points! I was very worried about EMI when I set out to build this and I had a long discussion with the experts at toroid.com. They are a really friendly bunch and very open to noob questions. I can only recommend working with them. It was a great experience.

Rudy

I can also vouch for the guys at toroid.com. They are the ones that designed and built my replacement transformer for my first Beogram 4000 project. They have some ready-for-sale transformers but they also design and build custom transformers which is what I had them do for my Beogram.

John

Interesting, come back with more, when you finish checking Beolover

Hi Martin,

The shield is not mu metal...I asked them when we discussed it. Some other alloy. The toroid is a custom designed one-to-one copy of the original transformer in terms of winding ratios and center tabs etc. That is why all the input voltage settings still work etc...it even has a thermal fuse like the original. So the circuit did not change at all.

The ill-performing transformer that you mention, was that a toroid or a EI-type?

Rudy

It was a toroid.

Martin