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Cabinet building and shielding
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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Sun Oct 01, 2006 12:44 pm    Post subject: Cabinet building and shielding
Subject description: Are shielded metal cabinets mandatory for 10V p-p ckts?
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So: I'm in the design phase of my modular-synth project, I've figured out panel sizes and materials, and I've scavenged an old hardwood table from which to fashion my cabinet. Very Happy

For panels, I was inspired by Roman Sowa, and decided to use 100x160mm fibreglass pcb stock. When reinforced with a length of 10x10x1mm aluminum L-profile (doubling as mounting bracket for ckt board), they don't flex much, and seem sturdy enough for plugging/unplugging 4mm banana's.
They're easy to drill, lightweight, and pretty cheap. Also, the copperplating is useful for shielding against incoming interference.

But:

For my synth to be completely shielded, I need it to function as a Faraday cage, right? So I need the copperplating on the back of my panels to touch a metal mounting rail, which needs to be part of a metal case.

So:

Is it really necessary? Did the ol' Moogs have metal cases underneath that yummy walnut? Doesn't any RFI have to be fairly powerful to be a problem in a system with 10V p-p signals? Of all the DIY cabinets I've seen pictures of, not one seems to take this into consideration.

If I wanted to do this, I would need metal mounting rails to contact with the panels. I could then bolt the panels to the rails, if the holes in the panels and the rails respectively weren't misaligned! I know that's going to be a problem, since I'm doing the drilling myself... Laughing
So if all holes are not perfectly aligned, I won't be able to move panels around freely. Using wooden rails would require much less precision, because then I could drive wood screws in whereever (not indefinately).
Of course RFI don't bounce of wood, so there's a problem.

Or what?
Am I worrying too much? Whaddaya say?

C
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Mikmo



Joined: Dec 01, 2005
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Location: Copenhagen - Denmark

PostPosted: Sun Oct 01, 2006 2:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

My synth (http://www.mikmo.dk/) is in a cabinet made from ordinary MDF sheet, no shielding at all, and i do not suffer from any interference problems.

I dont think shielding is required unles you plan to play in places with extreme radiosignals or electro magnetic fields.

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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Sun Oct 01, 2006 11:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, I guess if you put your synth on a stage with a big PA, lighting (and dimmers for that lighting), then you might get some interference. Or what?
Keith Emerson toured with a Moog the size of a house for years - was that one shielded? Or was it just not a problem?

My experience with the importance of shielding is limited to guitar stompboxes, but those things have internal signals in the millivolt range, plus many distortion circuits are high gain, which doesn't help. A good shielded box is essential in this case.

I huess it would be "best practice" to use a shielded case, but it would also be "most expensive-and difficult-to-make-yourself-practice". Rolling Eyes

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zipzap



Joined: Nov 22, 2005
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PostPosted: Mon Oct 02, 2006 4:41 am    Post subject: Reply with quote  Mark this post and the followings unread

I too have never had any problems without shielding. My cabinets are basically wooden frames that hold the alominium frontplate with the pots screwed in and circuitry hanging around.
The thing is this: As long as you use signals that are generated electronically and have high level (right from the start) nothing should happen. It´s really about gain. If you have input modules that boost a electric guitar to 10vpp so it meets the modulear standard things look different.
Now this has all been said, what i´m not sure about is if it is then enough to provide shielding for that single module.

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Uncle Krunkus
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PostPosted: Mon Oct 02, 2006 5:28 am    Post subject: Reply with quote  Mark this post and the followings unread

I've only ever heard of recommendations to use shielded cable for signal interconnections inside the module/synth, and that is definately not a necessity.
That's in spite of the fact that my ASM2 now resides inside this solid aluminium box which is basically it's own flight case and looks like it could survive an EMP! Laughing
I think the main thing to consider is the interference which can come from within the synth. Shocked The signal levels are often up around 10Vp-p true, but so are the control signals which are sitting right next to them, like the square wave coming out of an LFO, and the noise signal which is bundled into the same loom of wire. That's why they say to use shielded for your signals. The most important being near the output of the synth/module.

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Uncle Krunkus
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PostPosted: Mon Oct 02, 2006 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis wrote:
I huess it would be "best practice" to use a shielded case, but it would also be "most expensive-and difficult-to-make-yourself-practice". Rolling Eyes


I'd really recommend investing in a pop riveter, some sheet aluminium and some L stock aluminium. It took me years to discover how easy it is to knock up little boxes with this method. You'll love it!

And for reliable, round, accurate aluminium drilling;
Measure twice,
Centre punch,
Pilot hole (1.5mm),
And doweling bit. (They're the ones with a spike in the middle and the outside edges raised up)

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Coriolis



Joined: Apr 11, 2005
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Location: Stilling, Denmark

PostPosted: Mon Oct 02, 2006 11:06 am    Post subject: Reply with quote  Mark this post and the followings unread

How do I use shielded wire for signals, if I'm using banana jacks (no ground)?

Interestingly enough, one of the most deciding factors in my choice of materials for this (and other) projects, is the fact that I don't own a car!
So, for instance, aqquiring a sheet of plywood involves finding a way of transporting it to my home (a 2-room flat shared with my girlfriend and our 4-week old daughter). I would be paying for the wood+transport (don't know anyone nearby who has a car either - cars and fuel are expensive in Denmark).
Getting a sheet of aluminum is even worse. I wouldn't know where a private person (not having my own company) could buy stuff like that around here.
And how do you cut sheet metal in a way that leaves nice straight edges, using only cheap hand tools?

I'll stop whining now, Wink but let me just say, that these factors are pretty important to the way I DIY.
Naturally then, I would like to avoid making a shielded metal case Laughing

Other than that, your advice to get a pop-riveter is noted, Uncle K!
That's a no-brainer, now that I think about it (pun) - cheap and easy.
Btw: How do you go about bending sheet metal?

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Mikmo



Joined: Dec 01, 2005
Posts: 150
Location: Copenhagen - Denmark

PostPosted: Mon Oct 02, 2006 12:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok a little internal message from a dane to another dane on buying materials in Copenhagen :

Aluminiumplader får du småstykker hos skrothandleren, personligt bruger jeg den på Vandtårnsvej i Gladsaxe (lige om hjørnet) de koster næsten ingenting.

MDF plader køber jeg i "rest kassen" i småstykker hos Silvan, de koster typisk 20 - 25 Kr, og kan til nøds transporteres på cykel (jeg har først fået bil for nylig)

Hvis du mangler søjleboremaskine til print og den slags, så kan vi evt. lave en aftale jeg har en billig, men ok en i mit lille værksetd, kaffe er gratis Smile

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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Mon Oct 02, 2006 1:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hej Mikael!
Tak for tips om træ og metal. Selv er jeg mest til finsk birkefinér til kabinetter, men nu fandt jeg et sofabord i 25mm stavlimet bøg, i storskrald den anden dag, så det bliver mit kabinet! Cool

Når jeg nu tænker over det, havde jeg faktisk set på din hjemmeside at du fandt dit alu hos skrothandleren - sådan en er der vel også her på Amager hvor jeg bor. Det er mere det med at klippe panelerne til, der volder problemer. Jeg ser du bruger en nedstryger og en fil. Personligt hader jeg overdrevent filearbejde af et godt hjerte, og det larmer også for meget her i min lille lejlighed. Ved du om man kan klippe sådan noget alu pænt med en pladesaks? Altså uden det bliver bukket i kanterne, og sådan...?

Lyder hyggeligt med kaffe og søjleboremaskine, det går nu fint herhjemme med at bore i de printplader jeg bruger til frontpaneler (det kan en skruemaskine klare), men det kunne være sjovt at støde hovederne sammen engang, og udveksle erfaringer om byggeri generelt og specifikke moduler, hvad lyder godt, skidt, etc. Jeg skal nok lige have bygget lidt mere først - har 1 vco og 1 dual lfo næsten færdige for nuværende Wink .

Ser også frem til at høre nogen lyde fra din synth engang.

C
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Uncle Krunkus
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PostPosted: Mon Oct 02, 2006 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis wrote:

Når jeg nu tænker over det, havde jeg faktisk set på din hjemmeside at du fandt dit alu hos skrothandleren - sådan en er der vel også her på Amager hvor jeg bor. Det er mere det med at klippe panelerne til, der volder problemer.


I could have told you that! Rolling Eyes

Don't bother bending it. Get it cut to size and use angle stock for the edges.

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Coriolis



Joined: Apr 11, 2005
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PostPosted: Mon Oct 02, 2006 10:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, sorry about the dogspeak, I figured there might be some danish lurkers here who would like to know where to ask for aluminum scraps, so I posted here, instead of pm'ing Mikael. Wink

But you are right; forget about the bending... Smile

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Mikmo



Joined: Dec 01, 2005
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PostPosted: Mon Oct 02, 2006 11:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

An for cutting the panels to size i don't think a hand sheet cutter will do, the sheets you need ( 2-3 mm thick) really need to be cut with a "real sheet cutter". I just use a hack saw and file the edges, it's a pain in the neck and not ultra precise but it works. You can se the entire process here

http://www.mikmo.dk/synthpanels.html

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Uncle Krunkus
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PostPosted: Tue Oct 03, 2006 2:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I get my aluminium from a supplier in Coffs Harbour. It's not a big place, and is about 50km away, but they have about 8 different thicknesses of sheet aluminium, every L and U stock you could imagine, and they cut it on the spot for me. Dead square and accurate to 1mm(1/25")! Very Happy All I have to do is a bit of preparation knowing exactly what I want, and I get exactly that. And they charge half of what you'd pay at a hardware! Very Happy
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Coriolis



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PostPosted: Tue Oct 03, 2006 2:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Well that looks precise enough, I guess.
...but still a lot of work ! Wink

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zipzap



Joined: Nov 22, 2005
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PostPosted: Tue Oct 03, 2006 3:44 am    Post subject: Reply with quote  Mark this post and the followings unread

What´s a pop riveter?
About working with aluminium: I go another way. As i said my cabinets are wooden frames. I got a good price on some big wooden plates, they even look nice. And they cut them for me in the shop. The top and bottom are 50cm, the hight is about 18-19cm. Depth is about 17cm. For the frontplates i buy aluminium sheets that are 50*25cm, i cut them to three 25* 16,6 pices, two fitting in one cabinet.
The clou for me is to use really thin 1mm or even 0,8mm sheets.
They are cheap, sawed and drilled, even bent really easily. On the back i glue a thin wooden plate to stabilize the whole thing. Works very well.
I have a picture somewhere...
Since i have no good tools, no money and no space for working and i still say it works well i think i can recomend this methode.
I never cared about shielding, the bananas don´t cath any hum as well, no problem there.
As Uncle K pointed out it may be a good thing to use shielding at some points in the modular, although i guess most of the feedthrough from cv signals is due to the way cvs are applied in the modules.
What really helped me, of course i learned this here, was to use "star- powering".
In the beginning i had some problems with the clock (or the leds) of my sequencer clicking in the speaker. A LFO made similar problems.
Connecting critical modules directly to the psu solved this.
That was the only noise i ever had to deal with, had nothing to do with shealding, though.

found the picture here, it´s half assembled
http://electro-music.com/forum/post-83133.html#83133

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Coriolis



Joined: Apr 11, 2005
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PostPosted: Tue Oct 03, 2006 12:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
On the back i glue a thin wooden plate to stabilize the whole thing. Works very well.


Hmm, that's a good idea for someone like me...
It would be cheap, pretty easy to work with, and also very light, like the pcb-stock I use now, but maybe cheaper, and perhaps more flexible in terms of making panels larger than 100x160mm or whatever other sizes pcb-stock comes in...

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Mikmo



Joined: Dec 01, 2005
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PostPosted: Tue Oct 03, 2006 1:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

my first cabinet i is full now. One of my problems has been poor front panel real estate usage.

For my next cabinet i bought some special aluminium rack rails that you can slide square nuts into. that way i can make panels with different widths. I hope to get better space usage this way. The rails were rather cheap, but the nuts and screws were at expensive

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piedwagtail



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PostPosted: Tue Oct 03, 2006 8:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

i like acrylic,perspex,lucite meself.
b*gger to cut,b*gger to drill loves to catch you out occasionally though with a nasty crack....
but the colours..... Mr. Green

Robert
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Uncle Krunkus
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PostPosted: Wed Oct 04, 2006 1:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Robert,
again, when drilling things like perspex, use a doweling bit after a 1.5mm pilot hole, and you'll have perfectly round holes, all in a neat row, and you'll never crack it again.

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Coriolis



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PostPosted: Wed Oct 04, 2006 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

A doweling bit = stepped drill bit?

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piedwagtail



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PostPosted: Wed Oct 04, 2006 4:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Unkle K,
I have drilled so many holes in perspex on the bench press,that i know 97% will be error free.....its just the spectacular ripping up cracks you remember!
Smile
12mm is my speciality.
Flat wood drill bits are my favourite for boring Smile holing,rarely play up.
Spurpoint/auger styles are finickety sometimes just one size will rip relentlessly.
Twist drills are fine in sub 4mm,but above that become progressively more troublesome.
...great for frightening cracks.
All at a trundling 500rpm.
Handdrilling perspex is for gamblers.
Mr. Green
Robert
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Uncle Krunkus
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PostPosted: Wed Oct 04, 2006 7:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I've still gotta get a couple of those stepped ones.
On the Sorcerer I actually needed a 9.5mm so the stepped one wouldn't have helped. I ended up cutting my own from a 10mm one.

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zipzap



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PostPosted: Wed Oct 04, 2006 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

what are the steps for?
If seen it, but i don´t know how it woks.
How do you drill when there´s a step?

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Uncle Krunkus
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PostPosted: Wed Oct 04, 2006 3:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Each step carves another 1mm out of the hole. So you don't need heaps of bits to be able to drill any size hole. Just be sure you know when to stop.
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Mikmo



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PostPosted: Thu Oct 05, 2006 1:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Step drills are a godsend for drilling aluminium panels. Before i bought one i used to start with a small 2 mm drill bitt and then gradually step up all the way to the needed size. This involves a lot of bit changes. Now i can make hols up to 10mm without changing bits. And just as important you can use the same bit for deburring the back side of the panel again without changing bits. Much faster and cleaner holes.
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