looking for solutions to interconnection problems, shielding

Hey, folks,

I'm designing a custom pre-amp/mixer that fits inside a hurdy-gurdy. (Yes, really.) In the past I've just taken apart a commercially available unit and modified it to fit where it needs to go, but now I need to add some more channels and make it all work together.

I'm facing two design challenges that I'm hoping you all can help me to address: shielding and interconnection.

I have three boards that need to be connected to each other and to the inputs, outputs, and controls. These boards are inside the body and keybox of an acoustic instrument, so shielding is a potential problem. Is there something I can wrap them with? (Giant shielding shrink-tubing comes to mind, but there's no such animal as far as I know.) I know there's the shielding paint available, but it's an acoustic instrument and I'm loath to slather the inside of the body with a heavy metallic paint. How much metal do I need to have between the outside world and the board to protect the board, and how big of a hole can I afford in this shield?

On the intereconnection front: In the past I've simply soldered the wires to the board, but moving it around for testing and installation has broken the wires off, so I'm looking for another solution.

Ideally I would like to have the wires that run between the boards shielded also, yes? I've found some connectors that look as if they should work, either Molex C-grid or AMP MTA 0.100 series or some such (I think - I left my notes at home).

First interconnection problem: can I run a multi-conductor shielded cable from these little connectors by just connecting the shield to one or more of the pins? Or is there a better way to do this?

Second interconnection problem: both Molex and AMP sell a crimper for these connectors, for about $170. I was shocked until I found similar systems where the crimper was almost a thousand dollars. Do I need the crimper? I'm willing to get it if that's what I have to have to get the job done, but I don't want to just commit that much for something that I don't know will work. There's a cheaper Molex crimper - $50 - will that work?

I'm not trying to be cheap: I know the value of a good tool. I'm just asking if this is the RIGHT good tool.

I look forward to your replies,

Alden

You can buy aluminiun shielding tape for these sorts of applications.

Shielded cable and molex should be ok. You'll need to attach a thinner cable to the shield before attaching to a molex - it won't fit.

I've used the Molex tool and needle nosed pliars - both work.

Obviously the real tool is easier. I sometimes solder them to make the crimp stronger.

You may be over-thinking. Do you play hurdy-gurdy sitting on power transformers?

Steal a Fender Electric Guitar, pry the pick-guard or back plate off, and see how they do it. Often nearly-no shielding. Tight wiring, sheilded cable, and metal pots go far. The next step is some aluminum foil lining the body cavity and pinched under a grounded pot shell.

On my new collectable vintage Yamaha Wedge, all-plastic body, the circuit board has a cardboard cover with tinfoil on the side away from the board, clamped under a screw for grounding. There are many other things wrong, but it is quiet unless sitting on a power transformer.

I wasn't planning on sitting on a transformer... I have experienced some hum issues in the past, but they were usually tracable to bad connections.

The pots are metal. I've been using ribbon cable on the modified commercial units, but I'd prefer grounded cable if I can get it. The wires from the pickups (piezos) and mic capsule are shielded.

In the depths of my subconsious I figured the shielding wouldn't fit, so hooking it up to a smaller wire sounds good now that I'm actually thinking about it. Sounds as if I should try the budget crimper first.

Thanks, gentlemen!