SUT shielding

[farflungstar]

I'm looking at SUT's at the moment and am being tempted by the Dave Slagle custom wound transformers which he will make to precisely match a given cart (important I think).

Having owned and been very very happy with his autoformers (maybe in private exhibitions once my 'the Truth' linestage finally arrives - 6 weeks in customs up to now?) I'm confident he knows what he's doing.

But the price difference between naked and shielded transformers is huge. In copper, €470 without shielding, €2,200 with shielding - ouch!

So, how and with what can the transformers be shielded?

Adey

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[Barry]

I would have thought provided the SUTs have a low leakage inductance, any permeable (ferromagnetic) metal would do. Mumetal would be the best, but is has to be treated with care: sharp bends or holes drilled through it will damage the shielding properties.

[farflungstar]

I know Dave uses a very unusual mix of shielding elements including copper, steel, mumetal and maple - but mumetal is available, as is steel and copper. His hand built units are always first rate, top class affairs but by heck at a price.
Adey

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[Stryder5]

It is relatively easy to make a Faraday cage, not using any exotic materials or layers. Aluminium mesh ( or any material that is electrically conductive) is cheap and effective.

Google Faraday cage.

You can even protect from EMP by direct connection to earth.

Cannot understand why it should be so expensive?

[Barry]

A Faraday cage won't offer any shielding to magnetic fields.

[Stryder5]

A Faraday cage won't offer any shielding to magnetic fields.

You're right, it needs to be solid material for magnetic shielding.

[farflungstar]

I know mumetal can be bought on fleabay, likewise steel and copper sheets - I guess the issue would be making sure there were no gaps and that RCA's were well fitted. Considering how fairly priced Dave's stuff usually is there must be something 'special' about the enclosures and internals...
Adey

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[Barry]

You're right, it needs to be solid material for magnetic shielding.

It also needs to made of a magnetic material: iron, steel, nickel, mumetal etc.

[Light Dependant Resistor]

Would help to see the step up transformer type and differences being asked, an image or two ?

Toroidal type transformers are amongst the best for very low fields, hence looking at their construction
and why they offer advantage, may give some answers.

Given the amount of scrap metal available, and as long it meets requirements of safety, fashioning
a cover suggests the way to go.

[farflungstar]

The only pic I can find is if the transformers, the case is not a Slagle creation, it's a diy job.

http://i1078.photobucket.com/albums/w483/farflungstar/IMG_20170104_001113_593_zps5lne5ihi.jpg

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[Barry]

I suppose the obvious question to ask is are you already troubled by hum and noise? Is the case completely made of metal? And if so what is the metal - aluminium?

[RothwellAudio]

Dave uses a very unusual mix of shielding elements including copper, steel, mumetal and maple...
Maple? Really?
Shielding against magnetic fields requires a ferrous material, preferably of high permeability. It shouldn't really cost three times the transformers inside.
However, un-shielded but carefully sited transformers placed well away from mains transformers can have less hum than shielded transformers simply plonked down on top of another piece of equipment.

[farflungstar]

I'm sure that for just shy of 2k for the case I could come up with something....
Adey

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[Reffc]

Maple? Really?
Shielding against magnetic fields requires a ferrous material, preferably of high permeability. It shouldn't really cost three times the transformers inside.
However, un-shielded but carefully sited transformers placed well away from mains transformers can have less hum than shielded transformers simply plonked down on top of another piece of equipment.

This.


When I was developing SUTs, I used Mumetal shields and I can tell you, they don't cost £2K to make or anything close!

Shielding is really mandatory for small signals subject to and sensitive to EMI, it needn't cost the earth and can be simply effected by housing the transformers within their own (potted) shielded enclosures then placing those within a secondary shielded enclosure for good measure. It's also important to get the earthing right to avoid excessive hum.

[mac72]

Quite often to make proper magnetic shielding more than one enclosure must be used , is quite common to use steel shield as external one because of its high saturation then use mu-metal enclosures , as mentioned earlier bending should be avoided as it lowers mu-metal properties of the affected areas.
Very good remark about positioning and earthing, this shall be your first step , do it right and you might find no need for magnetic shielding

[mac72]

You're right, it needs to be solid material for magnetic shielding.

Not necessarily, as long as diameter of the hole is smaller than length of the wave :) , faraday shields protect from high freq. magnetic fields , we talking radio freq. above 100kHz when thickness of material used is around 1mm.
It could protect from 50Hz EM fields as well but thickness of used material must be more than skin depth of used material , if you want to use copper for example , we talking about min 20mm of thickness .

[Mike Adams]

I looked at some of Dave's SUT too.

They are quite a bit bigger than most SUTs and I believe Dave houses them separately, which I guess goes a little towards why they are so expensive. (I believe Jeff Day has some of these...)

In the end I chose to get HM7s as they are well shielded as standard which mean building them into a box was more within my skill base...

[Arkless Electronics]

My I ask the op has he considered a head amplifier instead of an SUT? There does seem to have arisen lately a belief in some quarters that a SUT is the best way of amplifying the small signal from a MC cart and that it is a better way than a good MC input on a phono stage or a head amp.... I strongly disagree! It's yet another of those "trends", "fads" based on "old wives tales" etc that unfortunately blight our hobby ;)

I make a high end head amp which, IMHO, is more than a match any SUT and will undercut the expensive ones as well :)

[Arkless Electronics]

Not necessarily, as long as diameter of the hole is smaller than length of the wave :) , faraday shields protect from high freq. magnetic fields , we talking radio freq. above 100kHz when thickness of material used is around 1mm.
It could protect from 50Hz EM fields as well but thickness of used material must be more than skin depth of used material , if you want to use copper for example , we talking about min 20mm of thickness .

You seem to be mistaking electromagnetic field and magnetic field....

[farflungstar]

The only reason I'm considering a SUT is for exact impedance matching of the shilabe with my Vida - the Vidas high setting is 100ohms but following the general rule of thumb of x10 means the shilabe should see 160ohms, though some folks prefer higher. I wish the Vida offered a higher setting as it's performance is astonishing as is the noise floor.

Adey

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[mac72]

You seem to be mistaking electromagnetic field and magnetic field....
Quoted from Wikipedia:
Faraday cages cannot block static or slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside). To a large degree, though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. For example, certain computer forensic test procedures of electronic systems that require an environment free of electromagnetic interference can be carried out within a screened room. These rooms are spaces that are completely enclosed by one or more layers of a fine metal mesh or perforated sheet metal. The metal layers are grounded to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference

[Arkless Electronics]

Quoted from Wikipedia:
Faraday cages cannot block static or slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside). To a large degree, though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. For example, certain computer forensic test procedures of electronic systems that require an environment free of electromagnetic interference can be carried out within a screened room. These rooms are spaces that are completely enclosed by one or more layers of a fine metal mesh or perforated sheet metal. The metal layers are grounded to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference

I stand by what I said :)

For proper screening against mains hum a SUT really needs mumetal or permalloy. Expensive stuff but not to the extent to double or more the price of a SUT!

[Arkless Electronics]

The only reason I'm considering a SUT is for exact impedance matching of the shilabe with my Vida - the Vidas high setting is 100ohms but following the general rule of thumb of x10 means the shilabe should see 160ohms, though some folks prefer higher. I wish the Vida offered a higher setting as it's performance is astonishing as is the noise floor.

Adey

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A head amplifier is far more flexible in terms of matching input resistance than a SUT, a Brucey bonus advantage there.... You can literally set it to any figure with no problems with a head amp. Careful with that "x10 rule of thumb" when it's cartridge matching we're talking about... it works reasonable if we were, for example, looking at what minimum value of pre amp input impedance should a phono stage with an output resistance of 100R look into. Although rather on the low side 1000R would work. With cartridge matching there is usually no particular appropriate value and one should just choose what sounds best.... Things are of course complicated by using a SUT as to minimise ringing and overshoot and maintain a flat response the SUT itself is fussy about loading... at both ends.

[mac72]

I stand by what I said :)

For proper screening against mains hum a SUT really needs mumetal or permalloy. Expensive stuff but not to the extent to double or more the price of a SUT!

Please explain then
You can't have a varying magnetic field without producing an electric field , third Maxwell equation says :a time change in a magnetic field produces an electric field, and the tendency of the electrical field to twist is proportional to the time rate of change of the magnetic field.

[montesquieu]

A head amplifier is far more flexible in terms of matching input resistance than a SUT, a Brucey bonus advantage there.... You can literally set it to any figure with no problems with a head amp. Careful with that "x10 rule of thumb" when it's cartridge matching we're talking about... it works reasonable if we were, for example, looking at what minimum value of pre amp input impedance should a phono stage with an output resistance of 100R look into. Although rather on the low side 1000R would work. With cartridge matching there is usually no particular appropriate value and one should just choose what sounds best.... Things are of course complicated by using a SUT as to minimise ringing and overshoot and maintain a flat response the SUT itself is fussy about loading... at both ends.

In theory Jez I'm with you on every point here and where someone is tearing their hair out over hum, I would always advise them to go active and be done with it. I've owned a couple of really good ones (Graham Slee Elevator and Denon HA-1000) either of which I would say are better than 90% of the SUTs out there and both of which (the Slee especially - and no doubt your own offering in this area as well) I'd be happy to live with.

BUT ... and for me this applies even to high end phono stages ... the best result from a musicality point of view in my experience is still a top of the range SUT ... in that I've been very lucky to own a Kondo era AN-S6c, Hashimoto HM-7s, a pair of Jorgen Shou transformers made for Ortofon SPUs, and the current transformers in my EAR 912. I don't know why this is, but even in a top-end stage like the Aurorasound Vida, the MC stage just isn't as good as the MM stage + top class SUT, I've seen this repeated time and time again where there are two gain options available.

Note that I'm not saying it's always better with MM input + any old SUT .. the opposite actually. SUTs have all the limitations you are talking about, and really good ones are rare and expensive ... but get it right and my experience is that it works better than trying to do it all with active gain.

[Arkless Electronics]

In theory Jez I'm with you on every point here and where someone is tearing their hair out over hum, I would always advise them to go active and be done with it. I've owned a couple of really good ones (Graham Slee Elevator and Denon HA-1000) either of which I would say are better than 90% of the SUTs out there and both of which (the Slee especially - and no doubt your own offering in this area as well) I'd be happy to live with.

BUT ... and for me this applies even to high end phono stages ... the best result from a musicality point of view in my experience is still a top of the range SUT ... in that I've been very lucky to own a Kondo era AN-S6c, Hashimoto HM-7s, a pair of Jorgen Shou transformers made for Ortofon SPUs, and the current transformers in my EAR 912. I don't know why this is, but even in a top-end stage like the Aurorasound Vida, the MC stage just isn't as good as the MM stage + top class SUT, I've seen this repeated time and time again where there are two gain options available.

Note that I'm not saying it's always better with MM input + any old SUT .. the opposite actually. SUTs have all the limitations you are talking about, and really good ones are rare and expensive ... but get it right and my experience is that it works better than trying to do it all with active gain.

I'm kind of with you to an extent, on most of it anyway. Certainly I'd expect a decent head amp to beat all but the "good++" SUT's all day long...
Where I differ is to just how good an active MC phono stage or head amp with good MM stage can get. I would say at least as good and often a bit better than the very best SUT's and, with the cost of a REALLY good SUT to add to that of a suitably good MM stage, often a fair bit cheaper. Of course all sorts of system synergy effects will come into play which can cloud the issue. The purchaser of the demo MkI head amp, "Alcarmicael" did I believe compare the Arkless head amp with the Hashimoto HM-7's when deciding which to buy and preferred the Arkless head amp by some margin, IIRC. I'm sure he will add his own ha'porth on that if he reads this:)

The forthcoming new Arkless Hybrid pre amp is MM in order that users can add their own SUT or head amp for MC use BTW. A later MC only version is intended as well but will cost considerably more.... but less than the MM version + a £1K SUT!

I'm planning on making another of the MKII version of the head amplifier for my own use and as a demo unit so when I get around tuit you're welcome to try it Tom. Maybe I can change your step up device preference:)

[montesquieu]

I'm kind of with you to an extent, on most of it anyway. Certainly I'd expect a decent head amp to beat all but the "good++" SUT's all day long...
Where I differ is to just how good an active MC phono stage or head amp with good MM stage can get. I would say at least as good and often a bit better than the very best SUT's and, with the cost of a REALLY good SUT to add to that of a suitably good MM stage, often a fair bit cheaper. Of course all sorts of system synergy effects will come into play which can cloud the issue. The purchaser of the demo MkI head amp, "Alcarmicael" did I believe compare the Arkless head amp with the Hashimoto HM-7's when deciding which to buy and preferred the Arkless head amp by some margin, IIRC. I'm sure he will add his own ha'porth on that if he reads this:)

The forthcoming new Arkless Hybrid pre amp is MM in order that users can add their own SUT or head amp for MC use BTW. A later MC only version is intended as well but will cost considerably more.... but less than the MM version + a £1K SUT!

I'm planning on making another of the MKII version of the head amplifier for my own use and as a demo unit so when I get around tuit you're welcome to try it Tom. Maybe I can change your step up device preference:)

Would be delighted to check it out.

[Mike Adams]

Just realised Adey is looking for a SUT to match the Shilabe with the VIDA (the end of the previous page)

From memory (Tom can confirm) the Shilabe did work OK with the VIDA, just the HM7s were a step up!

[farflungstar]

Yup Tom did find that the shilabe worked fine with the Vida, but that the SUT (hashimotos) was better. I'm in no rush for the SUT - lol the shilabe isn't in the house yet - but I research and plan sometimes months ahead before spending my hard earned money on possible expensive mistakes, and I'll be happy to live with it direct into the Vida for a month or so.

I have great respect for Toms opinion on audio - and have followed a very similar path (though I'm keeping the Vida lol and he's changed for the Ear) but I trust that if he discerned an improvement (system differences not withstanding) then I think it's a future possibility and upgrade.

To be honest SUTs scare the crap out of me, I just don't understand them, all those numbers and step up ratios and possibilities for mismatch that even a few ohms too low or too high can make or break quality. Hence my interest in Slagle who can wind them specifically for the cart - Tribute no, though he can include dip switches (I hate switches).

The Miyajima SUT may actually be perfect for me but I need the Truth and interconnects in situ to know whether a slight softening (which according to Tom is a trait of the SUT) is acceptable or a no no. With my current interconnects and Slagle Autoformer Volume I wouldn't want any softening.

Adey

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[RothwellAudio]

To be honest SUTs scare the crap out of me, I just don't understand them, all those numbers and step up ratios and possibilities for mismatch that even a few ohms too low or too high can make or break quality.
I think people get too worked-up about the idea of "matching" impedances where SUTs are concerned. It's different from power amp output transformers where there needs to be a match to the load for maximum power transfer. Certainly a 10 ohm cartridge doesn't need to see a 10 ohm load, and a 5 ohm cartridge doesn't need a different turns ratio from a 10 ohm cartridge. Personally I think I'd prefer to try something before I buy if possible, and that won't be possible if you get someone abroad to make something to order.