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-   -   Balanced / Differential Input Question (http://www.diyaudio.com/forums/solid-state/13041-balanced-differential-input-question.html)

thylantyr 28th March 2003 04:10 PM

Balanced / Differential Input Question
 
I want to clarify what the difference is between
differential and balanced.

I see various types of input stages, some
are single ended input (+sig and ground)
called "differential amplifier input stage" as
shown here;
http://users.ece.gatech.edu/~mleach/lowtim/instage.html

Then I see differential input balanced as shown here;
http://www.dself.demon.co.uk/balanced.htm

Is this statement true?
I can design a differential input stage that is either
has balanced or unbalanced inputs ?

Last question, there seems to be alot of pro
equipment with 600 ohm balanced outputs,
is this the industry standard to allow best
interfacing from one equipment to another
to minimize noise from long cable runs ?

Systems with 600 ohm output, is best performance
achieved if you connect it to a 600 ohm input
or can the input he 10k ohm balanced?

Do people concern themselves with the 600 ohm
design when doing home audio or is it just limited
to the prosound/broadcast industries?

tiroth 28th March 2003 04:36 PM

Quote:

I can design a differential input stage that is either
has balanced or unbalanced inputs ?
Generally speaking, yes, although the inverting input to the differential stage is often used for NFB. The stage itself, though, will happily accept either balanced or unbalanced input.

Quote:

Last question, there seems to be alot of pro
equipment with 600 ohm balanced outputs,
is this the industry standard to allow best
interfacing from one equipment to another
to minimize noise from long cable runs ?
I believe the spec is generally that the output will drive 600 ohm loads, presumably due to capacitive loading on long cable runs.

Quote:

Systems with 600 ohm output, is best performance
achieved if you connect it to a 600 ohm input
or can the input he 10k ohm balanced?
10k balanced would achieve better performance in virtually every case, I would think.

SisterOfMercy 28th March 2003 09:27 PM

Re: Balanced / Differential Input Question
 
Quote:

Originally posted by thylantyr
Last question, there seems to be alot of pro
equipment with 600 ohm balanced outputs,
is this the industry standard to allow best
interfacing from one equipment to another
to minimize noise from long cable runs ?

I don't think this is a standard. You want your output impedance to be as low as possible (with ease), and your input impedance as high as possible, to avoid losses in the output.
If it is true what tiroth says, that the output is able to drive 600 ohm loads I'll be really surprised! A 600 ohm input impedance is very low.. Haven't ever seen it though.

Several people explained to me the 600 ohms 'standard' isn't a standard at all, and people who don't do their design work allright use this.. So, I don't think people should design to this..


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