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In Reply to: Not quite true. posted by kurt s on April 9, 2007 at 12:22:34:
"It is not necessary to have one side grounded in a twisted pair to get benefit from twisting the wires, but it improves the situation."Hum rejection in twisted pairs generally depends on both wires having equal impedance to ground (i.e. 'balanced.') Neither is connected directly to ground. Having the same impedance, both pick up equal hum and noise with the same phase; the noise is common mode. A differential amplifier rejects the common mode noise. This is how twisted pairs are used in telephone systems, computer networks, instrumentation, pro audio, ...
Typically, the signal (music) is applied to both wires out of phase (differential mode) but it does not need to be; the music might be on one wire only (referenced to ground) so long as the other wire has the same impedance to ground it will pick up identical noise and the differential amp will 'subtract' it from the music signal.
This fact can be used if you happen to have a differential input amp but a SE output source. If you build an extra resistor network into the source that is equal to its output impedance you can use twisted pair to reduce hum and noise pickup in the interconnect.
What does any of this have to do with Jarthel's original question? I don't know. :)
-- Dave
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Follow Ups
- actually... - Dave Cigna 14:10:14 04/09/07 (3)
- Still... - kurt s 14:57:12 04/09/07 (2)
- Re: Still... - Dave Cigna 15:49:03 04/09/07 (1)
- Re: Still... - kurt s 08:03:02 04/10/07 (0)
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