headsets

500E · July 5, 2007

Normal conections for Nato plug

Tip = MicLo.

1 ring =Audio Hi.

2 ring = Mic Hi.

3 ring =audio Lo.

In some cases mic is reversed______________

2 sites with numerous plug descriptions

http://www.mobileone.com.au/headset/plugs.htm

www.flyingshop.com/acrobat/Connectors.pdf

PhotoFlyer · July 5, 2007

Mic Hi, Mic Lo? Audio Hi, Audio Lo? Which is ground?

500E · July 7, 2007

Mic Hi, Mic Lo? Audio Hi, Audio Lo? Which is ground?

Lo is normaly Ground

Another conector site

http://www.sennheiser.com/sennheiser/icm.n...Assignments.pdf

Gomer Pylot · July 8, 2007

It makes no difference. Both mic and speakers, each have two wires, and you can connect either wire in either position and it works, as long as you don't mix them. I've been making my own headsets for >20 years, and have never bothered with which mic or speaker wire goes where, and never had a problem. A multimeter is essential, though, for insuring proper connections with no shorts. With many cables it's very easy to get one of the hair-thin wires sticking out and shorting to another connector, so you have to make sure of the connections after they're made.

Edited July 8, 2007 by Gomer Pylot

500E · July 8, 2007

gomerpilot

How do you get electret microphones to work? as they are polarity concious.

I can understand with dynamic microphone.

Custom ear moulds arrived for the Mach 1 head set will report in next week or so

Gomer Pylot · July 9, 2007

I've been using electret mics for 20 years, and have never seen any indication that they know or care about polarity. Most headsets, especially David Clarks, have a cord from the mic that plugs into a jack, with the prongs side by side, and you can plug them in either way, 50/50 chance of getting it the same any time, and I've never seen a problem. I haven't used a dynamic mic in many years.

500E · July 9, 2007

Gomerpilot

Never found one that works with incorrect polarity, have never found one with no FET amp built in, strange, I presumed that aircraft microphones used phantom power.

Many types of microphones require power to operate, as a general rule these types are described as condenser microphones. The power is used for internal pre-amplifiers and polarizing microphone capsules. If internal batteries are to be avoided then the only solution is to supply the power via the microphone signal cable.

In some cases microphones might be claimed to be "dead" not realising that they require a battery or in other cases phantom power.

An electret microphone is the best value for money omnidirectional microphone you can buy. Electret microphone can be very sensitive, very durable, extremely compact in size and has low power requirements.

Electret microphones are used in very many applications where small and inexpesive microphones with good performance characteristics are used.

Electret microphone occupies (at a rough guess) the lower 90% of applications, quality wise.

Most lavalier (tie-clip) microphones, consumer video camera microphones and microphones used with computer sound cards are electret microphones.

The electret is a modified version of the classic capacitor (or condenser) microphone, which exploits changes in capacitance due to mechanical vibrations to produce voltage variations proportional to sound waves. Whereas the condenser MIC needs an applied (phantom) voltage, the electret has a built in charge, and the few volts needed are to power the built-in FET buffer, not to create an electric field.

Typical electret condenser microphone capsule is a 2 terminal device (there are also 3 pin capsules) which approximates to a current source when biassed with around 1-9 volt and routinely consumes less than half a milliamp. This power is consumed by a very small pre amplifier built into the microphone capsule which makes the conversion of very high impedance source of the electret element itself and the cable which needs to be driven. Be aware that this impedance is swamped at signal frequencies by cable capacitance so that at 1kHz the assembly will exhibit an impedance of a few 10's of K.

The load resistor defines the impedance and can be matched to the low noise amplifier intended. This is usually 1-10kOhm. The lower limit is defined by amplifier voltage noise and the upper limit by interference pickup (and amplifier current noise). Suitable resistance values are typically in the range of 1-10 k ohm. In many cases the microphone is powered from 1.5V-5V power source through a resistor which has resistance of few kilo-ohms.

Because the electret itself contains a small buffer amplifier which adds noise, it is common to specify a signal to noise ratio (usually at 94dB SPL) or self noise figure, which is the equivalent acoustic noise level, commonly around 20-30dB SPL.

Electrets need biassing because of the built-in FET amplifier inside the microphone capsule. Bias voltages should be kept clean, because the noise in this will get to the microphone output.

Basic electret microphone powering circuits

Basic circuit

+---------------------------- battery +Ve (3 to 12 Volts)

|

2k2 R1

|

o---------- 10uF ------o----- output

|+ |

CAPSULE 10k R2

|- |

+----------------------o----- Gnd, and battery -Ve

This is the basic electret microphone powering circuit which you can use as generic reference when designing circuits which use electret microphones. The output impedance is determined by R1 and R2. If you leave out R2 the output impedance is roughly the resistance of R2.

Here is another drawing of the same circuit:

Vcc

O

|

/

\

/

\ EQUAL TO REQUIRED IMPEDANCE

/ EX.= 1000 Ohm

\

|

| CAPACITOR MOST ANY VALUE 10uF 16v

|---| | + | /

| |---0----| |------- AUDIO OUT

| | | \

| |----O--------------

|---| |

|

-----

---

-

Battery powered electret microphone

This circuit can be used with normal tape recorders and sound cards which usually are designed for dynamic microphones. When you build this circuit inside the microphone case (or to small external box) you can make yourself an universal microphone out of an electret capsule.

10 uF

+ | |

+---------------------+--------| |--------------> to amplifier

| | | |

| (positive lead) |

| +----------/\/\/\---------+

MIC 2.2 k ohm |

| | +

| (ground lead) (-) -------

| (battery 9v or so) ---

| |

+-----------------------------------------------+----> ground

If you are building this circuit it would be a good idea to add a switch to switch off the battery when you do not use the microphone. You should note that the output signal level of this microphone is noticeable higher than the signal available form typical dynamic microphones so you have to turn down the gain in your microphone input (if there are no suitable adjustments then this higher level can cause distortion in microphone pre amplifier more easily). The output impedance of this circuit is around 2 k ohm so I don't recommend very long microphone cables to be used or you will loose some high frequency definition (few meters are no problem).

Super-simple powering circuit

In many cases it is possible to use one or two 1.5 V batteries (depends on microphone type) as a power supply for the mic. Battery is directly in series with the microphone.

----------- [ Battery ] ----------------------

I

----

Amplifier in Mic

----

I

----------------------------------------------

This circuit works if the microphone pre amplifier passes though some small CD current and is not bothered by it. This quite often the case but not always. Normally direct current from the battery has no influence on the preamp, as the preamp is only amplifying alternating currents.

If you do not know the right polarity of the battery, try it in both ways. In most cases wrong polarity at those low voltage should not cause any damage to microphone element, but can cause low or no audio.

The -Ve side of the insert usualy has a small strap to the case of the electret.

Gomer Pylot · July 10, 2007

Aircraft headset installations don't provide phantom power. They have to work with any type mic, and the headset mics have to work in any aircraft. Headset electret mics work just like dynamics, because they have to.

500E · July 10, 2007

Perhaps this is why people keep saying my headset does not work correctly,

& I still dont understand how a FET works without power.

Striped 2 smashed aircraft head sets both mics had electret capsuls with case of insert straped to one side of mic, wired to a amp would not work without applied voltage and corect polarity.

Gomer Pylot · July 11, 2007

Striped 2 smashed aircraft head sets both mics had electret capsuls with case of insert straped to one side of mic, wired to a amp would not work without applied voltage and corect polarity.

I don't understand what you're trying to say here. I just can't parse all that. If you're saying that you stripped two headset mics (previously smashed??) and they wouldn't work in an amp, then all I can surmise is that the amp you put them on wasn't the same as an aircraft avionics setup. All I know is that you can use an electret mic on a headset or helmet and polarity doesn't matter. Apparently there is additional circuitry in the mic that takes care of your concerns.