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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.
 

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Quote:
Originally Posted by Eduardo Barth  /t/1526074/i-need-help-with-xlr-connection-and-magnetic-shielding-materials#post_24574354

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.

The short answer is that most of the benefit of balanced connections come from the balanced input. A balanced input can provide nose rejection on the order of 40-60 or even more dB. A balanced output is good for at most 6 dB reduction in noise. You can drive a balanced input with an unbalanced output and if you do the wiring right you only lose the 6 dB benefit.
 

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Balanced cables offer as much as a 60 db signal-to noise ratio improvement over unbalanced connections because they are connected to a differential amplifier INPUT and output at both ends.


This fully differential circuit does not respond to outside hum and noise sources; only to the differential or signal voltage.


It also has the advantage that the cable shield does not carry signal current, as an unbalanced cable's shield must. Some form of additional shielding is of no use whatsoever, and would be a waste of money and time.


The balanced cable's inherent shield is all that is needed; a 2-wire balanced cable with shield. Stores commonly sell this as "microphone cable" in bulk, and you can attach the XLR connectors yourself, or you can just buy "microphone cables" with XLR connectors already attached.


These balanced cables and balanced mixers/preamps can be used for distances of 100 feet or more with no concern about hum or noise, even with low-output microphones (this is common in large halls for overhead recording session microphones), or other balanced source equipment.


Those are just as good as the "high-end" balanced cables sold for ridiculous prices; they work perfectly. "Premium" balanced cables are a waste of money. Gold connector contacts are desirable, however, and only cost a little bit extra.


The important thing is to understand that the entire CIRCUIT must be balanced; the output, cable, and input circuitry, or the advantage will not be achieved.


So the input circuit you design for the amplifier must be a differential amplifier circuit.
 

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Discussion Starter #4

Quote:
Originally Posted by commsysman  /t/1526074/i-need-help-with-xlr-connection-and-magnetic-shielding-materials#post_24574673


Balanced cables offer as much as a 60 db signal-to noise ratio improvement over unbalanced connections because they are connected to a differential amplifier INPUT and output at both ends.


This fully differential circuit does not respond to outside hum and noise sources; only to the differential or signal voltage.


It also has the advantage that the cable shield does not carry signal current, as an unbalanced cable's shield must. Some form of additional shielding is of no use whatsoever, and would be a waste of money and time.


The balanced cable's inherent shield is all that is needed; a 2-wire balanced cable with shield. Stores commonly sell this as "microphone cable" in bulk, and you can attach the XLR connectors yourself, or you can just buy "microphone cables" with XLR connectors already attached.


These balanced cables and balanced mixers/preamps can be used for distances of 100 feet or more with no concern about hum or noise, even with low-output microphones (this is common in large halls for overhead recording session microphones), or other balanced source equipment.


Those are just as good as the "high-end" balanced cables sold for ridiculous prices; they work perfectly. "Premium" balanced cables are a waste of money. Gold connector contacts are desirable, however, and only cost a little bit extra.


The important thing is to understand that the entire CIRCUIT must be balanced; the output, cable, and input circuitry, or the advantage will not be achieved.


So the input circuit you design for the amplifier must be a differential amplifier circuit.
 

My plan would be to buy Audio Technica Balanced Cables, that I have one for my condenser microphone of the same brand and it ever seemed to be flawless. They cost something around 20~30USD, that's pretty acceptable. So, I think I won't waste money at all.

 

Then, if I use the balanced output of my preamp and a balanced input in my amplifier, the signal would be cleaner, since, as I can see, the XLR connection is a more "clever" connection. It seem to justify the 50USD  (in the worst case) I'll have to invest on cables and plugs.


The thing is that once the signal get inside the amplifier, it will be amplified and will be outputed with cable pods, that, I think, are unbalanced to connect it to the red and black plugs in my speakers (yes, my speakers doesn't have the XLR connection and I don't really have money to buy a speaker with that kind of connection). Considering that, I would still benefit from the XLR connection being only between the preamp and the amp but having ordinary unbalanced connection between the amplifier and the speakers?


About the shielding, my idea wasn't to shield the XLR cable, but to shield all wiring inside the amplifier (that creates magnetic fields), to avoid the magnetic fields from introducing noise on the amplifier signal when it's being amplified or going from the amplifier module for the output. Can I benefit from that?

 

Thanks for your attention and have a nice day!
 

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Quote:
Originally Posted by Eduardo Barth  /t/1526074/i-need-help-with-xlr-connection-and-magnetic-shielding-materials#post_24575531



Then, if I use the balanced output of my preamp and a balanced input in my amplifier, the signal would be cleaner, since, as I can see, the XLR connection is a more "clever" connection. It seem to justify the 50USD  (in the worst case) I'll have to invest on cables and plugs.

You don't have to be too picky when you buy XLR cables. Usually durability is more of an issue than sound quality.


These look good to me, but ca. $20 each is not too much to spend for a good XLR cable:

http://www.monoprice.com/Product?c_id=115&cp_id=11509&cs_id=1150902&p_id=4754&seq=1&format=2
Quote:
The thing is that once the signal get inside the amplifier, it will be amplified and will be outputed with cable pods, that, I think, are unbalanced to connect it to the red and black plugs in my speakers (yes, my speakers doesn't have the XLR connection and I don't really have money to buy a speaker with that kind of connection). Considering that, I would still benefit from the XLR connection being only between the preamp and the amp but having ordinary unbalanced connection between the amplifier and the speakers?

Absolutely. Amplifiers rely on other means have hum free internal wiring. Grounding inside the amplifier is up to the amplifier designer, and this is a major factor related to hum and noise. The big concern is hum coming in via the input cable. Once the balanced input cancelt that out, things are usually under control.

Quote:
About the shielding, my idea wasn't to shield the XLR cable, but to shield all wiring inside the amplifier (that creates magnetic fields), to avoid the magnetic fields from introducing noise on the amplifier signal when it's being amplified or going from the amplifier module for the output. Can I benefit from that?

If you are designing the amplifier from scratch and you don't already know how to control hum inside the amplifer you have no business designing the amplifier until you have a better grasp of amplifier grounding. You would be better off to build a kit or follow complete instructions that already tell you how to do the internal grounding in detail.


The wiring inside a power amplifier is shielded by the amplifier's metal case, but it must be routed and connected with great care.


Here is an example of detailed instructions about how to wire a power amplifier internally:

http://users.ece.gatech.edu/mleach/lowtim/part2.html under "Wiring the chassis".




Figure 21 here may give you some hints: http://archive.siliconchip.com.au/cms/A_30872/article.html

 

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Discussion Starter #6

@arnyk  

Thanks for your post buddy, you really helped me to understand things better. Moreover, I'm building the amplifier with this kit:
http://www.aussieamplifiers.com/nxv800.htm

My idea is to have two nxV800 modules with everything in the 'not so budget minds', and have a dual monoblock inside the same chassis (I want to have some of the advantages of monoblocks, but I don't have space to have separated chassis, that's the only reason I'm doing it that way and I know it's very unusual). I just want to add XLR connections, since this amplifier has the balanced input. For the thoroidal amplifier I bought 2 used (the owner said he bought for a sound project that never came out of the paper) Piltron 2.2KVA which costed me 280USD the pair. I know it may be someway exageratted, but since it's going to be my main amplifier for at least the next 10 years (I hope so), I want to be sure that I won't have problems with it.

The magnetic shield I want to use is to protect the internal components from the magnetic fields that are generated by the internal components itself, for example, by the transformer. Magnetically insulating it from the rest of the internal components may give me a purer signal flow. At least, that's what I thought.

 

I'll just ask you one more thing, my friend: I will build the chassis myself and I've been thinking about using stainless steel or aluminium. What do you think would be the better option? Or perhaps, is there another better option? I know a lead chassis would be a better option due to its properties against any kind of radiation, but it's toxic and hard to get, so It's not an option.

 

Thanks for your attention and have a nice week!

 

Peace,

Eduardo Barth.
 
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