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Posted by Rob J on 01/09/06 03:02
In article <11s29f2bhc23s93@corp.supernews.com>, rcrowley@xpr7t.net
says...
> "Rob J" wrote ...
> > Richard Crowley says...
> >> "Rob J" wrote ...
> >> > We have a Panasonic MiniDV camcorder that has a
> >> > built in mic, the only input for external sound when
> >> > recording is a mic socket that can only be used with
> >> > an external mic from Panasonic.
> >>
> >> A review of the top 20 Google websites indicates that
> >> your Panasonic GS120 camcorder has an industry-standard
> >> 3.5mm stereo phone jack for a microphone input connector.
> >>
> >> Any conventional audio cable/adapter will work with your
> >> camcorder. For example, all of Beachtek's adapters appear
> >> to be compatible with your camcorder. They will allow you
> >> to connect a mono balanced source (as a tap from a venue
> >> sound system) into the mic input jack on your camcorder.
> >
> > Is Beachtek the only manufacturer of these devices?
>
> No, and there is nothing particularly "magic" about them,
> either.
>
> > It needs to block the phantom power that the mic
> > produces to stop this from going back into the desk.
>
> Capacitor. Around 50 cents.
I presume this is your web page:
http://www.rcrowley.com/CamAdapt.htm
For my application the camcorder sound feed will come from a desk line
send which can produce a maximum level of 21 dBu and to get a useful
range of signal level adjustment and also give some ability to calibrate
the level meters on the desk with the signal going out to the camcorder
the signal level needs to be padded.
The send out of the desk is at source impedance of 75 ohm and is
balanced. It will be coupled through an audio transformer for ground
isolation. We use these types of transformers for numerous similar
applications:
http://www.altronics.com.au/index.asp?area=prod&grp=355
http://www.altronics.com.au/index.asp?area=prod&grp=355&list=0&pg=1
&sort=code
Type M0705 M0706 M0707
For this application I would probably use one of type M0707 wired to
make a balanced to unbalanced conversion - one of the windings is centre
tapped. As the source is mono there is no need to have a stereo circuit.
A nice bit of icing on the cake would be signal level metering like some
of the Beachtek boxes can do. Perhaps using this kitset:
http://www.altronics.com.au/index.asp?area=item&id=K5412
Or maybe even this:
http://www.altronics.com.au/index.asp?area=item&id=Q0490
Here is a circuit for padding the audio level:
http://staff.ace.ac.nz/Centres/Technology/BruceWeb/Video%20in%20the%
20classroom/linemic.htm
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