Relax on the balanced output guys!

Posted by Andre Yew [IP: 208.8.104.2] on February 01, 1999 at 11:44:46:

In Reply to: Relax on the balanced output guys! posted by Chuck Swindoll, Jr. on February 01, 1999 at 01:02:27:

Hi Chuck,

I disagree with your assertion that:

:Secondly, if RF interference is your problem, line your walls with copper before you try to solve it with balanced lines as even a balanced line will give you fuss if you have that much RF interference.

That is overkill in the wrong direction, as many devices, like the Lexicon DC-1, generates much RF by itself already. A copper-lined room does not solve noise sources internal to itself like video signals, DACs, digital lines, TVs, etc. RF protection is gained by good design, and part of that good design is using balanced lines. I have seen and heard the effects of RF on my system from many seemingly innocuous sources, and I'd rather a have a well-designed system that protects against it rather than ineffective overkill like a copper room.

Second, hum in a system is caused by the non-zero impedance of ground lines, carrying return currents, which can be caused by using the shield of a cable as both shield and signal return. A properly implemented balanced system with no "pin-1" problems will always be ground hum and buzz free. Establishing a grounding stake does no good as the interchassis current will still be flowing through your shields which are shared as ground currents.

Third, a balanced system is not what you think it is. It does not involve opamps nor 6 or 14 dB boosts. The technical definition of a balanced system is one where the impedance from the "positive" pin and "negative" pin to ground and every other part of the circuit is equal, or balanced. That's it, and that's all you need for perfect common-mode rejection. Hence a balanced output or input can be implemented passively with no need for differential signalling (having the inverse of positive signal on the negative pin). I suggest you check out the Jensen transformers website and look at their app notes. Their analogy of a balanced interconnection to a Wheatstone bridge should prove quite enlightening.

--Andre

• Jensen Transformers

Follow Ups:

• Relax on the balanced output guys! - Chuck Swindoll, Jr. 16:46:41 02/01/99 (2)
  • Relax on the balanced output guys! - Andre Yew 11:17:16 02/02/99 (1)
    • Relax on the balanced output guys! - Chuck Swindoll, Jr. 13:28:53 02/02/99 (0)

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