I have a JVC GZ-HD3 and I would like to use an external mic. I dont want to buy the dedicated JVC item as I have plenty of mics that may be suitable. What is the configuration of the socket and what plug does it use and what is a suitable impedance for a mic? Thanks

You can get the required at  www.radioshack.com What is Microphone Impedance?All microphones have a specification referring to their impedance. This spec may be written on the mic itself (perhaps alongside the directional pattern), or you may need to consult the manual or manufacturer's website.
You will often find that mics with a hard-wired cable and 1/4" jack are high impedance, and mics with separate balanced audio cable and XLR connector are low impedance.
There are three general classifications for microphone impedance. Different manufacturers use slightly different guidelines but the classifications are roughly:

1. Low Impedance (less than 600ω)
2. Medium Impedance (600ω - 10,000ω)
3. High Impedance (greater than 10,000ω)

Note that some microphones have the ability to select from different impedance ratings.
Which Impedance to Choose?High impedance microphones are usually quite cheap. Their main disadvantage is that they do not perform well over long distance cables - after about 5 or 10 metres they begin producing poor quality audio (in particular a loss of high frequencies). In any case these mics are not a good choice for serious work. In fact, although not completely reliable, one of the clues to a microphone's overall quality is the impedance rating.
Low impedance microphones are usually the preferred choice.
Matching Impedance with Other EquipmentMicrophones aren't the only things with impedance. Other equipment, such as the input of a sound mixer, also has an ohms rating. Again, you may need to consult the appropriate manual or website to find these values. Be aware that what one system calls "low impedance" may not be the same as your low impedance microphone - you really need to see the ohms value to know exactly what you're dealing with.
A low impedance microphone should generally be connected to an input with the same or higher impedance. If a microphone is connected to an input with lower impedance, there will be a loss of signal strength.
In some cases you can use a line matching transformer, which will convert a signal to a different impedance for matching to other components.

This one has a standard mini-jack mic input.


let me know if you need further assistance
thanks
Kevin