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Balanced 1/8"?

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Tony Connoly
Balanced 1/8"?
on Nov 10, 2010 at 2:28:05 am

Is there such a thing as a balanced 1/8" microphone connection, or are all 1.8" microphones unbalanced?


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Eric Toline
Re: Balanced 1/8"?
on Nov 10, 2010 at 12:14:15 pm

There could be a balanced 1/8" (3.5mm) connection but every one I've ever seen has been unbalanced.

Eric


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Bill Davis
Re: Balanced 1/8"?
on Nov 10, 2010 at 8:13:12 pm

Eric is precisely correct.

Balanced wiring requires 3 separate conductors so that you can implement a wiring plot to pass a ground PLUS two legs having inverted phase with respect to each other down the cable. So there's no technical reason you couldn't use any small 3 conductor connector in a balanced scheme. But since these small plugs and sockets are typically among the most FRAGILE size and style connector, they are hardly EVER used for balanced wiring. More typically these are used for unbalanced stereo audio.

In all my years around audio, I've NEVER seen a balanced audio system that uses mini-pin wiring.



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Tony Connoly
Re: Balanced 1/8"?
on Nov 10, 2010 at 8:45:23 pm

I was watching a training video on lynda.com called Digital Audio Principles by Dave Schroeder where he refers to the stereo 1/8" mini plugs as "TRS" and "balanced", and the mono versions as unbalanced. So I am confused by what he was trying to get at.


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Eric Toline
Re: Balanced 1/8"?
on Nov 10, 2010 at 10:31:29 pm

TRS means Tip-Ring-Sleeve. In a normal unbalanced configureation as for headphones the tip is the left channel, the ring is the right channel and the sleeve is the ground.

To have a true balanced connection you must have 3 connections for each in/output as in an XLR connector. Pin 1 is the ground, pin 2 the positive, pin 3 the negative.

You can unbalance an XLR to an unbalanced connector by jumping pin 1 to pin 3 in the xlr but you will lose about 6db in level. Any connector with only 2 connections (tip-sleeve) is an unbalanced connection.


Eric


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Tony Connoly
Re: Balanced 1/8"?
on Nov 11, 2010 at 2:20:38 am

Fantastic. Thank you Eric and Bill.


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Jordan Wolf
Re: Balanced 1/8"?
on Nov 13, 2010 at 5:15:20 am

Eric & Bill, et al.

Not to be pedantic, but balanced wiring is kind of a misnomer. Whether or not an input/output is balanced is completely independent on the wire used in connecting it. A balanced connection is made by having the same impedance (Z) on each leg of the circuit. The 3rd wire (Pin-1, Sleeve, drain, shield, etc.) doesn't matter in the balancing of the connection.

The 3-wire mic cable uses Pins 2(+) and 3(-) for carrying the balanced signal and Pin 1 for keeping the gear attached to it at the same or low enough voltage potential. This keeps ground loops to a minimum. The shielding and twisting of the pairs helps with EMF and RF interference. The only place that NOT having all 3 connections becomes problematic is when you require external phantom power for a microphone or a DI box, since +48V uses Pin 1 as it's ground reference. Cat5e cable works very nicely for multiple balanced, line-level signals (and there's no "Pin 1").

Additions and corrections are welcome; hope the above was informative and helpful.

Wolf
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Dave Haynie
Re: Balanced 1/8"?
on Mar 6, 2011 at 6:40:21 am

[Jordan Wolf] "Not to be pedantic, but balanced wiring is kind of a misnomer. Whether or not an input/output is balanced is completely independent on the wire used in connecting it. A balanced connection is made by having the same impedance (Z) on each leg of the circuit.

Kind of. The term "balanced" actually means that you have an impedance match between source, cable, and sink. But in nearly all use, implied by the term, as well, is that you have a differential signal pair run across balanced twisted pair cable. The ground can be a DC reference and a shield, and doesn't hurt, but it's the differential signalling that's largely responsible for the noise rejection. So a "balanced" cable is certainly part of the system... the twisting and impedance match is necessary. The cable on its own, though, does not make a system balanced.

For those unfamiliar with the details, a singular signal is made differential by a differential driver, which has matched amplifiers producing inverted and non-inverted copies of the signal. When run across impedance controlled twisted pair, any external noise that's accumulated will be nearly identical between the two wires. At the terminal, the two signals are subtracted from one another... the common mode signal (all that noise) goes to zero, the differential mode signal (the original) is restored.

-Dave


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Jordan Wolf
Re: Balanced 1/8"?
on Nov 13, 2010 at 5:16:34 am

A 1/8" connector could be used for a balanced connection if it and the connections were wired correctly. Otherwise, you'll get cancellation of anything that's in mono (the same on each leg).

Wolf
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