I need help with XLR connection and magnetic shielding materials!

[eduardokbb]

Hello! First of all, although you may understand what I'm saying here, I don't speak english very well. So perhaps you'll find some typo errors in my post and, sincerely, I'm very sorry for that.

I'm building a stereo amplifier myself. In my final system, I'll use a preamp to make the digital to analog conversion and it will send the signal for my amplifier, which will amplify it and send the amplified signal for the speakers. My preamp have XLR connection, and I'm here to ask if it would give me some kind of benefit if I put XLR inputs in my amplifier to make use of the XLR on my preamp (I know I paid an extra price because of that XLR).


Well, I'm building the amplifier myself. I'm trying to use the best quality components that may give me a more reliable and good sounding amplifier. My point is to get best sound quality, but I also know the value of my money. That said, I won't waste money using pure 16AWG silver wires for the internal wiring, I'll use high quality 12AWG OCC Copper. Its just to explain how I'm investing my money, so you won't give me options that will cost my soul.

I remember that when I was at school, I learnt (or learned?) in some physics classes that when there is electric current going inside a cable or anywhere else, it creates a magnetic field outside the cable. If that's true (and I think it is), my entire amplifier will have magnetic fields everywhere there's a wire, but it will happen mainly on the thoroidal transformer (and in my sketch there are two really strong thoroidal transformers). That said, I thought that all those magnetic fields could, somehow, interfere in the good flow of the current introducing some noise. There are several ways to shield cables/wires against magnetic fields, and I'm thinking on covering the wires with Nu-Metal (magnetic shielding material) and covering the Nu-Metal with insulating tape, since the Nu-Metal is a conductive material, and it could cause really undesired problems. For the amplifier module, thoroidal transformer and other components I would make a kind of enclosure (with enough space to able the components not to fry, of course) with holes to get the wires in/out. Inside this enclosure I would put some layers of Nu-Metal covered with insulating tape. The inside of the amplifier chassis would be entirely covered with some layers of this Nu-Metal. It would cost me something around 200USD to do this entire magnetic shielding stuff. Do you think it could, somehow, make things work better and protect the system against undesired noise? Do you have a better option to do that? Or, perhaps, is it a complete waste of money?


Thanks for your attention and I hope you could understand what I'm asking here. If you can't, please, ask me that I'll try to explain it better. I really need your help with that.


Peace,
Eduardo Barth.

 

[jinjuku]

Is this amplifier from a kit?

 

[Speedskater]

My thoughts:
a] The more current in a wire, the greater the field.
b] In a wire pair (send & return) almost all the field is cancelled at a distance of 10 times the spacing between the wires.
c] Only the output stage and the power supply need heavy wires.
d] It's Mu-Metal or Mumetal. The "Mu" is from the Greek alphabet.
e] Toroidal transformer's have much less external field than plated transformers.
f] Only if your sensitive input stage is near the transformer will you need extra shielding.
g] The "DIY Audio" forum is excellent source of information for new amplifier builders.
http://www.diyaudio.com/forums/amplifiers/

 

[slipperybidness]

How about using wire that already has its own magnetic shielding?
shielded wire - Parts Express Ships Fast and Ships Free.

As another memeber mentioned, using 16AWG for every connection is overkill, you only need that on particular connections.

Yes, there is a benefit to using XLR connections, and many like the fact that most XLR connections lock into place. You get even more benifit (CMNR) with a fully-balanced design, but that is a more complicated build as it just about doubles the parts count.

Here's a few books that might be useful
High-Power Audio Amplifier Construction Manual: G. Randy Slone: 9780071341196: Amazon.com: Books
http://www.amazon.com/gp/product/0071379290/ref=wms_ohs_product?ie=UTF8&psc=1
Designing Audio Power Amplifiers: Bob Cordell: 9780071640244: Amazon.com: Books

I'm getting ready to build some projects out of that Audiophile Project book myself.

Depending on how far along you are on your project, you may want to check out these kits
http://ampslab.com/

 

[Speedskater]

While those cables are shielded, they are not magnetically shielded. There is a lot of fine print that goes with magnetic shielding.

 

[eduardokbb]

How about using wire that already has its own magnetic shielding?
shielded wire - Parts Express Ships Fast and Ships Free.

As another memeber mentioned, using 16AWG for every connection is overkill, you only need that on particular connections.

Yes, there is a benefit to using XLR connections, and many like the fact that most XLR connections lock into place. You get even more benifit (CMNR) with a fully-balanced design, but that is a more complicated build as it just about doubles the parts count.

Here's a few books that might be useful
High-Power Audio Amplifier Construction Manual: G. Randy Slone: 9780071341196: Amazon.com: Books
The Audiophile's Project Sourcebook: 80 High-Performance Audio Electronics Projects: G. Randy Slone: 0639785330820: Amazon.com: Books
Designing Audio Power Amplifiers: Bob Cordell: 9780071640244: Amazon.com: Books

I'm getting ready to build some projects out of that Audiophile Project book myself.

Depending on how far along you are on your project, you may want to check out these kits
Power Amp Kits by AmpsLab

Thanks for your reply buddy. But I'm already doing a kit. My goal is to make a "two monoblock inside one chassis" of the 'not so budget' nxV800, as you can see in the link below:

HPA-nxV800 800 Watt MOSFET Audio Amplifier Module

Since it can push up to 500w RMS per channel, I think I might need to use thicker cable. For the transformer I bought 2x 2246VA Piltron Toroidal Transformer, that seemed to be high quality and I could get for a really nice price.

I'll study how to do what I want entirely balanced. Thanks for your reply buddy!

 

[highfigh]

If you're going to look for more info on the shielding material, look for Mu-metal it's a combination of copper and nickel. I used it for shielding car stereo head units and cable bundles- it worked well, but it wasn't much fun to work with because the material that was available was very thin and the edges were incredibly sharp, It did work, though.

However, if you look inside of most preamps and power amps, you won't see this kind of shielding often, if at all.

The standard practice is to bundle low level wiring separately from anything with high current and if their paths must cross, it should be at 90 degrees to keep the magnetic fields from coupling. Also, keep all of the high voltage and high current away from the low level signals.

Good luck with this project.