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Old 12th January 2004, 02:53 PM   #1
tiagor is offline tiagor  Portugal
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Default toroidal trannies alignment

Hi,

a lot has been said about the alignment of transformers to avoid the influence of it's magnetic fields. I was wondering if similar precautions should be kept in mind with toroids.

Following is a diagram of the layout that I was thinking of. The larger ones are the output. They are spaced only about 1.5cm apart. May I run into any problems?

Thanks,

Tiago
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Old 12th January 2004, 09:26 PM   #2
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Yes, good job you hesitated....From your diagram, it seems from my reconing the mains toroid is only a 5cms from the input tubes.....that's much too close for comfort..(MI okay but Hi Fi NO!) ..) The most serious problem is the optimum orientation of the mains tranny related to the input tubes for min hum. This is where a conflict might occur as whats optimised good for one channel may be lousy for another. That's what I found with mine. The culpit is the leakage inductance flux, with uneven or gappy windings may spew-out in more than one place, making optimisation difficult. If you have full flux-density toroids, i.e 1,6T Bmax and unscreened i.e without a steel band on the outside, then the optimisation (or null in mag field) related to the input tubes and earths might be difficult to optimise. Rotation of the mains toroid is all one does to obtain the lowest hum. So leave leads long..for this.
The golden rule prevails with any mains tranny, lo or hi flux. E&I core......keep it well away from the sensitive input tubes.
I would re-orientate mains toroid in oppos direction i.e towards the rear, the furthest path away from input tubes.
As you have a stereo chassis (I assume); the interaction between o/p trannies will be small because NFB lowers the effective o/p impedance...however in saying this, it's possible of a small interaction but usually not serious. A symmetrical layout does help, especially reducing induced hum due to differing earth paths within the chassis. One method I've had alot of success with is an earth system based on using a thick copper busbar grid and earthed only at a common input end for both channnels. I hope

I'm not appearing to complicated but this is good in avoiding co-channel interation. It would be a pity to assemble then to find worse is for worse, and pays to spend some time getting the mechanical layout as best as poss.


What circuit arrangement are you using, expected input sensitivity etc.....and layout idea of internal components ? what test equip (if any) do you have ?

rich
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Old 12th January 2004, 11:10 PM   #3
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Hi, richwalters -

How effective might a 0.4 mm thick mumetal band around the the power toroid be, and how wide should it be relative to the height of the (horizontal) toroid to be effective? Or should I use something else? I have a somewhat similar situation where I'll have a couple of input tubes about 4 - 5cm from a toroidal power transformer in my next project however with no flexibility in my spacing.

thanks in advance -
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Old 13th January 2004, 10:48 AM   #4
tiagor is offline tiagor  Portugal
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Thanks for the comprehensive answer Rich,

in fact the tubes were about 5cm apart from the trannies. I guess I'll throw the mains further back to increase the distance to the input tubes.

Quote:
One method I've had alot of success with is an earth system based on using a thick copper busbar grid and earthed only at a common input end for both channnels.
That's what I was thinking. One ground for both channels, and one ground for the PS. Still wondering if the should be connected to earth though.


Quote:
What circuit arrangement are you using, expected input sensitivity etc.....and layout idea of internal components ? what test equip (if any) do you have ?
The amp does not have preamplification, it will be fed directly from a cd player, the input tubes job is only phase splitting.
Test equipment consists of signal generator, DMM and a 2 channel scope.(Could you please tell me how can I use the scope to fine tune the trannies alignment to best possible position?)
Also, it is in fact a stereo chassis, and it will not have negative feedback.

Thanks,

Tiago
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Old 13th January 2004, 07:21 PM   #5
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Is there anywhere that sells covers for transformers, toroids for instance?

I have one I'm using now and, although it looks nicely made, it's not really made to be looked at. For example, the wiring details are printed on a neon orange label under the protective cover. The only other option is to buy them in a plastic cylinderical enclosure.

I thought they might look a bit better with a prett-ehy cover... I must be weird right?!

Also, is there any particular brand name that uses nicely insulated leads?

I am using one by Nuvotem at the moment. While it serves it's purpose perfectly well, the instulation on the leads is horrible! I think it's PVC or something like that. It melts if it so much as warms up.
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Old 13th January 2004, 09:13 PM   #6
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Re screening toroids......A solution I used is to make a steel “container” (2-3mm thick mat) enclose bottom and sides and toroid sits insideThe sides must be slightly higher than the tranny. . (Workshop job) The important bit is to weld the bottom to the sides (all way round), and provide a hole for lead outs and mounting. The case can be screwed to chassis but leave tranny to be able to rotate to null magnetically..However, I assumed you had an input tube but without that you could get away without the “container” bit. But the rule regarding location <furthest away from input> sticks.
Scrapping 35dB input end gain makes alot of difference!

I’m against mumetal simply because awkward shapes and unwanted bending ruin the shielding properties, and solution is probably easier with steel. (only my opin). Give it a go if you have material. Given the close proximity with the input tubes, then it pays to take whatever measures to avoid radiated hum problems. It would be a pity to scrap a design because of crummy noise performance.. As frank rightly mentioned, <we listen to the hum>.

However in your case with no input tube /nor feedback, dramatically changes the situation. As you mention line-in from CD player direct to cathode coupled phasesplitter and p-p o/p stage, you would easily expect 20Watts + with EL34’s with luck 2% THD with matched tubes 20% taps and dynamic balancing.......assuming gain of 22 in phase splitter. But I’m only guessing on the back of my hand with beer in the other. Perhaps your config is other. IS IT ??

< Unfortunately the world is becoming depleted of good toroid manufacturers, of those who really understands the feel of the flux. and proper winding techniques.> As for the poster regarding toroid covers etc, I can’t help on this one. The donuts (toroids) look horrible, I always mount under chassis, space permitting.

): rich
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Old 14th January 2004, 01:15 AM   #7
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Hi,

Most toroids I know of have very small magnetic field.

Regardless of that nice feature, I never use any in audio gear...

Guess why?

Cheers,
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Frank
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Old 14th January 2004, 02:00 AM   #8
tiagor is offline tiagor  Portugal
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Quote:
However in your case with no input tube /nor feedback, dramatically changes the situation. As you mention line-in from CD player direct to cathode coupled phasesplitter and p-p o/p stage, you would easily expect 20Watts + with EL34’s with luck 2% THD with matched tubes 20% taps and dynamic balancing.......assuming gain of 22 in phase splitter. But I’m only guessing on the back of my hand with beer in the other. Perhaps your config is other. IS IT ??
Hell no THD should be no more than ~0.8%, 30W max output, EL34's connected as triodes. The phase splitter has an amplification factor of 14. Hmm.. I think that's about it.

Regards,


Tiago
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Old 14th January 2004, 07:51 AM   #9
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just checking

rich
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Old 14th January 2004, 08:25 AM   #10
SHiFTY is offline SHiFTY  New Zealand
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Quote:
Is there anywhere that sells covers for transformers, toroids for instance?
I am also looking for some square 80mm pots for some OPTs.

One idea I had was to go to a supermarket/gift shop where they have a lot of boutique tins of tea/coffee etc. A nice tin upside down painted well would look pretty good. However I haven't done this yet.

Maybe you could find a round tin for a toroid?
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