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Old 16th July 2007, 10:31 AM   #1
dejanm is offline dejanm  Austria
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Default RCA/XLR input ?

Hi,

I have seen that Pass Labs in their X.5 series of amps uses XLR and RCA inputs. External jumper is used for easy switching between these two input types.

Does naybody have schematic of this solution ? Does anybody know whether Nelson Pass uses some kind of curcuit for transforming single-end connections into balanced and vice versa ? I believe that Nelson does not use transformers for this ... but I really do not know.

The reason why I ask this question is that I would like to have a balanced input on my amp. I already have pre-amp with transformer at the output with XLR outputs and now I am looking for a simple solution to implement balanced input on the amp side ..

Regards
Dejan
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Old 16th July 2007, 10:45 AM   #2
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Aren't these amps intrinsically internally balanced throughout?

Look at my website for a balanced input module
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Old 16th July 2007, 11:51 AM   #3
dejanm is offline dejanm  Austria
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Quote:
Originally posted by richie00boy
Aren't these amps intrinsically internally balanced throughout?

Look at my website for a balanced input module
My amp will not be balanced - therefore the question ...

I looked into your schema. Looks good ... Thanks ...
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Old 16th July 2007, 07:29 PM   #4
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The X amplifiers intinsically have a balanced input, so no
conversion is necessary. If you have a more conventional
topology, a differential input is not difficult to implement. I
suggest you take a look at the A75 article for a comprehensive
discussion.

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Old 17th July 2007, 08:05 AM   #5
dejanm is offline dejanm  Austria
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Quote:
Originally posted by Nelson Pass
The X amplifiers intinsically have a balanced input, so no
conversion is necessary. If you have a more conventional
topology, a differential input is not difficult to implement. I
suggest you take a look at the A75 article for a comprehensive
discussion.

Thanks a lot. I know this great piece of circuit from this article:

http://cygnus.ipal.org/mirror/www.pa...om/balzenp.htm

But, still ... if I have pre-amp with transformer balanced outputs and if I use balanced cable, wouldn't be enough to simply connect two inversed inputs within the amp (which is not balanced anyway), without implementing any particular circuitry for that ? I am actually reffering to this article:

http://www.jensentransformers.com/an/an003.pdf

On page 3, Fig. 3.1 the author is referring to that ... in only one short sentence though. Does it mean that if you have implemented pre-amp output as balanced by using transformer, that you have simply to connect hot and cold inputs together in the power amp in order to conform with the non-balanced (dual mono) architecture of the power amp ? Or is it still better (higher CMRR, perhaps) to implement kind of transformation curcuit like for example differential input (Pass solution) or transformer (Jensen solution) ?

Regards
Dejan

P.S. Sorry for asking such a basic questions, but I am still learning ...
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Old 17th July 2007, 08:08 AM   #6
dejanm is offline dejanm  Austria
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and one more question: if it is true that in the power amp it is sufficient to simply connect two + wires together, does it make any sense to use balanced connection between pre-amp and amp in this situation ? Or simply using SE RCA connection will provide the same result ?

I have also SE RCA outputs on my pre-amp.
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Old 17th July 2007, 09:31 AM   #7
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If your only aim is to eliminate ground loops, just having one transformer in the system is enough. Whether that is at the source output or the amp input it doesn't really matter.
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Old 17th July 2007, 10:37 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
your transformer has two wires for the output.
You can use a screened cable between your balanced source to the receiver.
The two signal wires must not be connected together at the receiver.
The screen can be left unconnected at the unbalanced receiver, your system may be quieter this way.
The two signal wires should be connected to the signal input and to the signal ground when the receiver is unbalanced.
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