Intact Audio

I have sourced some Mumetal cans that are suitable as a first line of defense for SUT's and these then need to be placed in a copper lined steel enclosure to finish the job.

the basic shape of a pair of the shielded SUT's is a 2.5" X 4.9" cylinder and this sets the minimum dimensions for the steel box. Details on how I assemble the naked SUT's into the mumetal cans can be found at:

http://www.intactaudio.com/forum/viewtopic.php?t=1609



Please feel free to suggest enclosures here and I will comment about their suitability. In the next few days I will document the enclosing of the SUT's in the cans and then others can chime in with pics of their build process.

dave

http://www.intactaudio.com/forum/viewtopic.php?t=1609

the hammond 1454M at 3" X 4" X 6" looks to be a workable choice. It is 20ga steel and a pair of 2-1/2" capacitor clamps will hold the mumetal cans in place and there should be plenty of room to mount some RCA's and a ground lug.

http://www.hammondmfg.com/pdf/1454M.pdf

the hammond 1458C4 is a bit more but has thicker steel and looks to be a bit easier to work with. If you go for this series make sure you get the one with solid sides. The vented side version has a "V" in the part number.


I'm sure there are plenty of others so it is up to you to look and post links and pictures as a road map for others to follow.

dave

The best one I've found so far is another Hammond that I found on Parts Connexion. I can't post the url, but its code is HAMMOND-55477

it's too long (17"), but the format is good and I'm happy that I could do a neat job of shortening it to say 8", giving final external dims of 8 x 4 x 3

Still looking...




the 55477 is a choke so it must be another hammond number.

dave

The easiest way to mount the mumtal cans is to use a 2.5" capacitor clamp like this.


assuming a 3" tall enclosure I would then use a piece of 1/4" plywood to shim it up and give some "air" between the steel and the mumetal.

dave

I’ve also been looking at the Hammond 1415b as a good option. There’s a more expensive 6�x6�x3� stainless steel junction box that would also work (RS Pro 7491857 at Allied), but I think the lower cost Hammond will be fine with some hammered paint.

popthropologist wrote:I’ve also been looking at the Hammond 1415b as a good option. There’s a more expensive 6�x6�x3� stainless steel junction box that would also work (RS Pro 7491857 at Allied), but I think the lower cost Hammond will be fine with some hammered paint.

the 1415b will not fit the mumetal canned SUT's because the foldovers for attaching the top and bottom will reduce the opening to around 4-1/2 inches.

Stainless steel is typically non-magnetic and is ineffective as a magnetic shield.

dave

dave slagle wrote:

popthropologist wrote:I’ve also been looking at the Hammond 1415b as a good option. There’s a more expensive 6�x6�x3� stainless steel junction box that would also work (RS Pro 7491857 at Allied), but I think the lower cost Hammond will be fine with some hammered paint.

the 1415b will not fit the mumetal canned SUT's because the foldovers for attaching the top and bottom will reduce the opening to around 4-1/2 inches.

Stainless steel is typically non-magnetic and is ineffective as a magnetic shield.

dave

Good to know! Ok, but the Hammond 1415c should work, right? Is 20 gauge steel too thin?

yes the 1415C will fit them and ultimately the thicker the steel the better the shielding. 20ga would be the minimum I would consider. From an assembly perspective the 1458C4 uses thicker 18ga steel and looks like it would be the easiest to mount RCA's into and solder. A wood front could easily be added to dress it up.

dave

EDIT

The 1458C4 has aluminum front and back panels so they would need to be covered with steel to be effective shields.

IT looks like the 1454L would work well. Appears to be all steel and has plenty of room inside as well as a form factor that will allow everything to be mounted and then the cover put on.

The Hammond case I was talking about is actually PN 1441-20 - dunno where that choke PN came from ...

The 1458C4 looks like a good fit with no modification, so that is probably the better choice anyway.

Looking at the datasheet for the 1458C4, the top and bottom covers are steel, but the front and back plates are aluminium. I'm guessing that is not appropriate if we are looking for all around magnetic screening, so I'm now searching again. I may go back to the 1441-20 as it's all steel, albeit 20 ga and too long so it'll need to be shortened.

Nick

wow... you are indeed correct the front and back of the 1458C4 are indeed aluminum. My solution to this would be to with the box in hand measure the inner dimensions of the case and get two roughly 4"X6" pieces of 20ga steel cut and install them over the aluminum. The front will be easy and it can simply be epoxied. The back looks like you could use some 1/2"-1" standoffs to mount it floating off the back panel to leave room for the RCA Jacks and two small holes with grommets will allow for the wires to pass through.


If you go with the 1441-20, how would you cut it down? My best guess is the large size isn't a problem from the SUT's perspective just from a placement perspective since SUT's can occasionally be position sensitive.

dave

i found a simple steel box from BUD Industries on amazon. Is 16ga steel too thick to work with using my simple tools?

I went ahead and ordered it, and canceled my order of the Hammond with aluminum fronts and backs.

The part number of what I ordered is BUD JB-3952 (not able to post links yet). It does have a small hole in the back meant for grounding, but I figure I can seal it or screw in something there to plug it up.

If it doesn’t work, Amazon has easy returns. But I’m eager to get going on this project!

that bud box looks like it will work.

dave

The BUD case looks like a good find - right size and 16ga steel!

I've ordered one too

Today I received the JB-3952 steel case. It is perhaps one of the smallest form factor cases that would work for this project; the fit will be tight once everything is installed and wired up.

4 steel footers should work well in the bottom panel screw holes—or maybe there’s a different elegant solution that isn’t occurring to me?

The 2.5� capacitor clamp fits neatly into the case. I am toying with the idea of securing it to the top lip of the case instead of the bottom, because the diameter of the screw holes on the capacitor clamp matches the holes in the case. There does need to be a ~1/8� nut between the case lip and the capacitor clamp for this solution to work completely.



I’ve begun applying copper tape to the case lid:


But before I go copper wild, I’d love to know how these SUT wires should be connected to the RCA in/outs so I can drill the necessary holes in the case. Dave?

Make sure you do a dry layout for this ship in a bottle. Using RCA's that mount from the back will make things much easier since the whole thing can be soldered up outside the box and installed. The attached picture gives the basic wiring info. I connect the input and output grounds together and have het to have noise issues in a properly grounded system.

Holes cut, picture taken 2 coats in. It’s now a dark gray hammered finish. Waiting for it to completely dry before applying the inside copper shielding.



I sourced rear mounted RCA jacks from Manley via eBay. They are low profile, require 1/2� chassis holes, and should be a good fit inside the box.

I started with the thought that I would make my copper lining look super clean, but that went out the window pretty early on as I started working with the adhesive.

Where did you get the copper tape from? I'm waiting for my case to arrive, but may as well get the other components on order too...

Thanks, Nick

NickC wrote:Where did you get the copper tape from? I'm waiting for my case to arrive, but may as well get the other components on order too...

Thanks, Nick

Yep, this is what I got:
https://www.amazon.com/dp/B01I1XNY1E/re ... pDbWQAJXGT

Jon

Thank you! Some on its way now. I've also ordered some RCA sockets with external securing nuts and a ground post, so should be ready to start installation very soon.

I'm planning to make a couple of hoop clamps like the one posted above, with the intention of mounting both them and some feet through the 4 holes in the base - with a pad to raise the transformer case off the base enough to avoid the raised earth point.

Dave: should I clean off the surface finish to ensure good electrical contact between the steel case and lid, and do I need to fill the centre hole in the earth point with something ferrous, or can I just tape over it with the copper tape?

yes... abrate the mating surfaces to get conductivity and no the center hole does not need to be filled. The hole will essentially disappear magnetically once you get past 1/2 the hole diameter away from it. A corollary to this is a cylinder is considered infinite once the ends extend the cylinder diameter beyond the item being shielded.

dave

Final Q before I start soldering--I plan to solder the transformer ground wire to the ground lug on my chassis, but do I also need to ground each of the RCAs? (I have shoulder washers to keep the chassis from touching the RCA plugs).

I connect all of the grounds of the RCA's together and then do a single connection to the ground lug. I also ground the chassis and transformers to the ground lug.

Many people feel the need for a ground lift switch to break the connection from the signal to the case and some go as far as to also switch the ground connection between the primary and secondary to "break" ground loops. My take on this is to eliminate the cause of the ground loop rather than trying to apply a band-aid by using a ground loop.

dave

I finally had time yesterday to finish the project and solder everything together.

The good news is that it is boosting the signal compared to my MM phono pre. And there is no hum--it's completely silent.

The not as good news is that the bass is very recessed. The highs and mids sound great, however.

Could this be an issue with my soldering?

No, it was an issue with me inattention to detail. Everything was—and is—working perfectly. No hum.

The trickiest part is threading the RCAs into the chassis, but that’s what we all played Operation for as kids!

Sounds good - I'm glad you found the issue quickly!

I'll post when I've made progress too, I'm tied up with other jobs at the moment