Powering Powering By Chris By value that will allow long cables to becables to microphone long allow will that value hungry circuitry normally requires purpose-made purpose-made requires normally hungry circuitry power- their of case since aspecial something ar valves USusing (tubes, parlance) in 500mW nearer 50µW as low as be 100-200mW might of order is the microphone of a commonly for requirement power total The possess. inherently dynamics most that performance Level Pressure Sound extreme sacrificing risk they so doing in that argue would some though source impedance, consistent more or ability driving cable greater give to buffer to allied that been have microphones (including afew dynamic of ribbon) introduction further field The even is complicated bythe need donot escape power. the but for circuits DC impedance high with associated problems of avoid the some to order in anddemodulator oscillato use, asmall designs instead, RF capsule. the polarising for power additional need also calledinaccurately more even “truecondensers”) Non-electret capacitor (sometimes microphones way. some in be powered needs to andthis – circuitry transducer the behind immediatel out by an carried is matching, or conversion, impedance This interference. exclude to help will and efficiently driven lower amuch reduced to be to needs impedance cable.This of length ashort even – anything to directly connect to impossible them makes output high which impedance extremely an and have parameter, electrical energy butmodify generate an donot “condenser”)microphone transducers called inaccurately, though (popularly, Capacitor acable. down distance atsome feed generous, to not apreamplifier adequat that is atalevel impedance low relatively energy electrical from athey - generate powering need any donot microphones dynamic Simple Woolf output some for designs. high Microphone

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to prove since some of the alleged benefits are benefits alleged the of some provesince to them. with “positive” Nagra recorders. with earth been for have reversed with use polarity made microphones pin2, some pin1). However Tuchel “positive” applied (XLRbeing the to leg phase a12V the +12 only in form, with exists It circuit. usual the shows Figure 2 61938 IEC standards. the of 7.5 by section covered is powering Parallel of such defects of rather them. than oblivious better be to aware However connection. existent be screen might it intermittent non- an or have cables that poor with T-power operate to possible also is prerogative. It not their is exclusively that something – use common in microphones power T- of impedance output verylow the with connected one adifficult is claim This phantom. than robust more that claim is it ManyT-power of users past. the producedin variants power T- have andother companies use everyday in still are designs Sennheiser older of number aconsiderable capsules of range but Colette the for preamplifier CMC4U Schoeps andthe MKH416T Sennheiser the are marketed phones T-power the only writing of micro- Atthe time other for microphones used fear for of damaging be must not T-power using lines microphone that system, in incompatible an is It industry. TV and film the in adherents some finds butstill obsolete nearly is powering) parallel or powering, A-BTonaderspeisung, Tonader, (alias T-power phantom. ubiquitous and the almost rare rather T-power, the – these of covervirtually all configurations powering andconsidered two are powers adequate lower voltages and microphones professional of semiconductor-buffered the vast For majority T-Power powering powering

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treat astandardtreat balanced aspair asingle rails is rejected very efficiently. rejected very efficiently. is rails power phantom the on noise so immunity same the gives of microphones powering Phantom by become has power system phantom The Phantom Power cur- rents with opposite polarities on each leg. leg. each on polarities opposite with rents cur- signals differential as wanted handle they because out such cancel interference Balancedcircuits flowed cur-rent leg each down this circuit. of signal phantom identical an pair balanced since effect no had the formed on so circuit phantom The wires. anyextra without circuit additional conductoran and, earth by using return, create an could they realised who engineers bytelegraph used technique from ingenious an its takes name It arrangement. compatible and elegant an andis the number of other disadvantages that have have that disadvantages other number of aare ribbon, there microphones particularly and to dynamic, T-power with lines microphone connecting dangers accidentally of the Besides power section. the beyond by switching changed be canonly phase signal so unavoidablyare linked polarit andpowering signal that noted be should It agroundedsupply. with connection unbalanced permits that circuit normal avariant of shows Figure 3 the signal. audio the for symmetry terms of in convenient more may This one grounded. leg bebe to for allows standard the unbalancedsystems. However also to connection simple very for allows which 12V The respect be with may , to floating most common microphone powering method method powering microphone most common Figure Figure Unbalanced 3 - Microphone +ve +ve phase (Tuchel or or (Tuchel connector XLR shown in brackets) brackets) in shown connector

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far far al Pwrn Input Powering Cable or or parallel y takers and is discontinued. discontinued. is and takers it would would it better be much read you to there. for it covers Library] great the subject authority with an the Microphone Data Jörg by article Wuttke [within Phantom” Feeble “The power but here phantom possible be agreat write would to about It deal but found atone time no was (P24) introduced A portableequipment. 24V as in premium, version ata is power of economy advantageswhere a12V some variant common andavailable has is and7.4 clause though the 48V the most is version 61938 IEC is power for phantom standard The reduced. greatly is rail power crosstalk of microphones risk the same between on andt critical less significantly is supplies power Thus the filtering for requirements anddecoupling therefore needs to be exceptionally well filtered. filtered. well therefore needs exceptionally be to andvoltage signal the on superimposed is voltage powering loop. powering be that provided outside functions -must the attenuatio andLF provided line usefully alsovices Many necessarythese de-powering circuits. of the have not did frequently recorders and mixers byminiature 9Vaof pairdriven since batteries. PSUs portable regulated from powered were microphones location T-power many Historically contributed to its limited appeal. The supply appeal. The limited to its contributed similarly be of a high order. ahigh of be similarly must -supply rail common audio of the viasignals leak the pre-vents that decoupling the -isolation the mutual systems microphone multiple powering powering

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their coils and . andtransformers. coils their poses no danger - no net current will flow within within flow will net current dangerno -poses no microphones intended balancedfor operation dynamic of connection the maintained up made and correctly are cables Where path. DC aclean canprovide and continuous is connection screen cable the that require however does stereo It useful MS rigs. recording in may that be atpossible something - any point is andinversion phaseso signal the of terms in polarity not sensitive is cabling power Phantom Compatibility Accurate matching is needed needed is for matching Accurate phantom microphones. microphones. current they are on asthough al- XLR not met as well shown are connections Figure Tuchel 4. shown is in circuit P48 termed - conventionally reference For astandard 48V phantom - Microphone +ve +ve phase Microphone +ve +ve XLR shown in brackets) brackets) shownin numbering connector DIN or (Tuchel

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Phantom powering of other micro- the capsule. This can give them a higher susceptibility to interference than might phones otherwise be expected. The ubiquity of phantom powering means that it is often called upon to power microphones that are not essentially designed for use in this way. A Digital Phantom Power number of small electret microphones - typified by The standard for digital microphones is gradually lavalier designs - which are inherently unbalanced, settling into a consensus that is described by and suitable for connection to radio transmitters AES42-2001. The reliability and compatibility of and other non-standard inputs, may also be useful the phantom system commends itself for digital for operation with conventional balanced inputs. transmission paths just as it does for analogue They can be converted to use with phantom ones. supplies with some form of powering adapter. Figure 6 shows a possible configuration. Such The output voltage level of the data is 2V and the adapters vary considerably in their sophistication. phantom voltage is fixed at 10V . The range of Some use additional semiconductor buffering to current anticipated is much higher than with further reduce output impedance and thus analogue microphones - 50mA is considered a improve the ability of the microphone to drive mini- mum and the maximum is 250mA (though lines. while others use transformers. In many 500mA has been mooted). cases the design also permits an option of battery powering. In theory the cabling with its XLR-3 connectors is compatible with analogue microphones but the However not every design achieves perfect line practicality of mixed analogue and digital balance in both AC and DC terms, and some environments has yet to be resolved. require rather unusual grounding arrangements at

- 10µF 2

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Figure 6 - Phantom powering of an electret capsule

Reference: The Feeble Phantom - Jörg Wuttke (Microphone Data 2003)

This article also draws on an earlier publication, “How to Power and Connect Professional Micro- phones” by Jörg Wuttke (Schalltechnik Dr.-Ing. Schoeps GmbH)

Chris Woolf is the editor of Microphone Data and has a long association with Rycote.

©2010 Microphone Data Ltd

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