Unbalanced 2 Conductor Cables

Wiring Microphone cables balanced to unbalanced

Connecting 3-pin Balanced to 2-pin Unbalanced Inputs

In the commercial audio world, professional audio devices such as compressors, limiters, equalizers, line amplifiers, mixers and such use balanced audio inputs. Commercial microphones have balanced outputs. Balanced inputs use a passive, wide-response transformer or active circuitry, usually referred to as differential inputs, to create a balanced signal input.

Balanced connections employ two conductors, each of which carries the same signal but with the polarity of one reversed with respect of the other, located inside an isolated shield which is usually connected to an earth or chassis ground. The term "push-pull" is sometimes used for describing the output of power amplifiers, not line-level circuits. The beautiful feature of a balanced audio line is that, when the signal cable is subjected to an interfering signal, that interfering signal is equal on those two conductors; but since they are out of phase, that noise is canceled and all that it left is the desired audio signal that has the opposite polarity and therefore does NOT cancel.

Unbalanced connections can work just fine in small sound systems, or in fixed systems where ground loop problems can be eliminated once, and then forgotten. It is best to avoid, in audio systems that drive radio transmitters, as their audio input cables are subjected to the RF output of the transmitter. In a balanced input, that interfering RF signal would be canceled just by the nature of how a balanced audio input works.

The shield of a balanced signal connects to ground, usually just ONE end to avoid any ground loops. Any interfering signals that land on this shield are immediately dumped to ground, but what DOES land on the out of phase, balanced input lines inside of that shield is canceled.

Type of Cable

The shield for a balanced audio signal when subjected to high RF environment ideally should be a 100% silver braid, not the foil type with a "drain." Heil Sound has solved this audio cable problem with our new "Heilwire" cable. Two #18 gauge stranded conductors are inside the silver 100% braid and outside of that shield are two #18 gauge control wires for push to talk (PTT) or other control functions. It's the perfect wire for audio signals.

Balanced to Unbalanced Connections

All amateur radio transmitters (except the new Yaesu FTdx9000) unfortunately use an unbalanced microphone input. It's sad, but true. In connecting a balanced microphone, equalizer, or audio device that uses balanced signals, care has to be taken in how the balanced signal is UNBALNCED in order to feed that unbalanced input.

The nature of the active output of the mixer or EQ determines the type of cabling that may be used when that balanced output is connected to an unbalanced input. The two conductors inside the 100% shield of the "Heilwire" should be employed, allowing the cable to remain more or less balanced right up to the input of the unbalanced device. This actually helps cancel noise, because the shield drains noise to the earth ground and is not relied upon to carry the signal. The shield's finite resistance means that grounding the shield and the "low" side of the cable at the input to the unbalanced device is not the functional equivalent of doing so at the output of the balanced device potential, but with the polarity of one reversed with respect to the other.

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Not too difficult

by heres_what_ya_need

You need a mic (could be lavalier or wireless -- about $100)
a microphone pre-amplifier
a headphone amplifier (4 to 8 outputs)
and long cables to plug the listeners' headphones into the headphone amp.
i cannot think of a way to get wireless connectivity to multiple sets of listener headphones-- i imagine that the radio-frequency wireless headphones from radio shack will conflict, but have no experience with them.
cheers!

Shure Incorporated Shure A15PRS Switchable Phase Reverser
Musical Instruments (Shure Incorporated)
  • An in-line switch permits instant selection of either normal or reversed polarity for comparison purposes.
  • Corrects polarity reversal caused by a wiring error in a microphone cable
  • Can be used for reducing phase cancellation/comb filtering between two signals that are of opposite polarity

Gadgets from Hyderabad, Fin & more  — Free Press Journal
These include microphones, headphones, telephony accessories, and avionics headsets for consumer, professional, and business applications. Sennheiser was in the news recently with the launch of its PMX 95, PCX 95 and PX 95 headphones in India.

RDL Manufacturing RDL DS-TPSL2A Active Two-Pair Sender - Twisted Pair Format-A - XLR Microphone & Stereo RCA In Power Supply Included
CE (RDL Manufacturing)
  • Design simplicity, ease of installation, unsurpassed flexibility, automatic fused power, exceptional hum rejection, low noise, and low distortion provide designers...
  • Balanced Microphone XLR Input with Phantom; Switch-Selectable Mic Gain on Rear Panel; Two Unbalanced -10 dBV Phono Jack Line Inputs
  • MIC Feeds Pair A; L and R Summed to Mono Feed Pair B; Remote Powering through Twisted Pair Cable; Fused Local Power Feeds all Connected Modules
  • Local Power Input on Terminal Block Blue;LED Indicates Module is Powered
  • Utilizes Two Format-A Pairs; Studio-Quality Precision Active Balanced Circuitry
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