Availability Of Toroid Xformer Cans??/

[highbias]

Does anyone know if anyone stocks a standard size range of cans to shield toroid? I have one that has a bit too much radiated field and is inducing some hum into the wiring. I've experimanted with re-routing the wiring and have got it to the minimum that I can without a decent shield at this point. This transformer has no electrostatic shield or any other type of shielding at the moment.

Thanks,

Mark

[janneman]

Mark,

I know this doesn't answer your question, but toroids have the lowest radiated field you can get in a normal transformer. If you have problems with it, the real problem may be the receiving part.
Metal (copper, aluminium, whatever) cans will NOT (or only a little) screen the 50Hz field from the toroid anyway.

Jan Didden

[highbias]

Hi Jan,

The problem I am having is that the input leads (Mogami single conductor shielded) are picking up the magnetic flux from the toroid. Yes, moving and re-routing the input wires did help substantially. But there is still a small trace of hum that I want to get rid of. The odd thing is that there is more hum induced by magnetic flux from the toroid than from running the input lead right next to the AC wiring at the other side of the back plate. I wonder if wrapping the toroid with a steel band would help? This is an unbalanced Aleph 3. I have some Star-Quad cable here that I may also try replacing the Mogami with but that is generally only effective with a balanced circuit.

I don't have even the slightest trace of hum in my Aleph 2's and I used basically the identical layout with the 3. They too are running unbalanced at the moment.

There are photos of this amp at this location....
New Aleph 30 In Progress

Thanks!

Mark

[janneman]

Well, as I say, I am very much doubting what you say is caused by the transformer hum. Especially as you say that moving the lead to the AC wiring is better.
You may have an earthing issue. Are you ABSOLUTELY sure that the gound points and loops are exactly as the other amp?
Is it possible to move the transformer temporarily say 2 feet away and run the amp that way, to see what the hum does?
Hum bands around the transformer are sometimes used with E-I cores as they DO radiate, I haven't seen them used on toroids.

BTW nice stand-offs on that heatsink. Where did you get those?

Jan Didden

[highbias]

One difference is that the boards in this amp do have a ground plane where the 2's don't but they are wired about the same. I will experiment some more and move the transformer around a bit.

Those terminals you refered to are called Turret terminals. I buy them locally and can't remember who makes them off the top of my head. They cost 70 cents each but the price is well worth it. They are also VERY sturdy and come in many different styles. The size of these is approximately 16mm above the threaded part, about 5.5mm of threaded part and the hex is 6.35mm in diameter. The thread is 6/32.

Here is one source for them..... http://www.staffall.com/

Mark

[janneman]

Thanks for the link Mark.

Jan Didden

[highbias]

Looks like I have it licked. I re-wired the inputs with Canare Star-Quad and re-routed the input wire. Have done the left channel so far and its dead silent. I also twisted the secondary wires comming from the toroid to the bridge and to the star ground point. Hopefully the right channel will be as good.

Mark

[janneman]

Originally posted by highbias
Looks like I have it licked. I re-wired the inputs with Canare Star-Quad and re-routed the input wire. Have done the left channel so far and its dead silent. I also twisted the secondary wires comming from the toroid to the bridge and to the star ground point. Hopefully the right channel will be as good.

Mark

Good job! Seems like you know what you're doing.

Jan Didden

[jacco vermeulen]

Why not fold a metal plate and cover the toroid with it ?

Saves looking for expensive pans, easy to fasten to the chassis, and you could have them done in SS.

My guess would be that you experience hum despite the same layout because the orientation of toroid magnetic fields is not constant.
The wiring around the core may not be exactly the same, the tension of the cable wire may differ, or the core differentiates.

I suppose the hum is not caused by toroid vibration ?
The look of resin molded toroids i like a lot, epoxy resin has excellent qualities for toroid molding ;
no mechanical vibration and vibration induced hum, better heat transfer from the transformer than through air, and a steady groundplate for fixing the toroid to the amplifier chassis.
I have used alloy outdoor cooking pots to mold toroids in.

A shame that MU metal has become so filthy expensive, i still have a bunch of cinch plugs with MU metal outer tubing.
As far as i have gathered MU metal is the only material able to shield magnetic fields highly effectively, MU metal foil worked wonders on the moving coil phono stages i built.

[highbias]

Well, its all back together with re-wired inputs in Star-Quad and it is lots better but still no cigar. This amp is wired by the book... literally. About 98% of the hum is gone now and its quite listenable. I still had to orientate(rotate) the toroid to get it this low and I don't recall ever having to do that on any other amp projects I've built in the past. With no input to either channelm or just one input connected its dead silent and no hum at all. I can't remember an amp that I've had this much trouble with. I am actually thinking about getting a different toroid to try in there.....

Mark