At 09:23 2007-03-22, you wrote:
>Klas, you wrote:
> > Hmmm.. there are very few "fully balanced" microphones today. Most of
> > them, even the MKH series for example, (and R=F6de NT1A) have pin 3
> > just AC grounded. So oscillation occurring internally in the mic,
> > will go straight into pin 2 and never get outbalanced.
>
>Are you sure? As far as I know, all common phantom-powered microphones
>provide a balanced output. I just googled for microphone circuits and
>found this very interesting page that exlains the principle of the MKH
>microphone series:
>
>http://www.beis.de/Elektronik/HF-Mic/HF-Mic.html
That surprises me, as I am sure that I have seen a MKH -diagram with
unsymmetrical output. (I have never taken a MKH apart) Can they have
changed it? Or have I seen a simplified diagram of MKH20?
>I admit that it is quite difficult to fully understand that circuit.
>Though, it is clear that pin 3 is not AC grounded!
>
> > The only way I know that mic electronics can make an unclean phantom
> > power even worse, is when something in the circuit starts to
> > self-oscillate. But such an oscillation is easy to see on the scope.
> > And the PRO6 handle is actually only a simple filter and source
> > follower!? Quite conventional and fully established.
>
> > And why shouldn't PRO6 work with a semi-pro machine like the Fostex,
> > when it works fine with a cheap consumer machine like the Zoom H4??
>
>Is pin 3 of the PRO6 really AC grounded? If so, this unusual
>asymmetric design could be the reason for the problems with some
>recorders.
No, it is not a "unusual" design. Most electrets (Nakamishi etc.)
have unsymmetrical outputs, but a balanced cable. Also "true"
condensor microphones, as NT1A, for example. (Which I HAVE taken
apart so I know for sure.)
>As I mentioned before, a microphone that provides
>complementary AC output signals on both pin 2 (+) AND pin 3 (-),
>should be less demanding regarding any potential phantom power noise.
>If you use an asymmetric design, there should be no AC grounding on pin 3!
The two signal leads (2,3) must "see" the same impedance, otherwise
the input will not outbalance disturbances in the cable. Pin 3 must
therefore be grounded via a resistor and a capacitor simulating the
same impedance as the signal output.
If there was some internal oscillation in the PRO6, which could be
outbalanced, I would have seen that on the scope.
I need to say this again - this noise has appeared only with MT24/96
and Fostex FR2.
The PRO6 works fine with Zoom H4, Tascam DAP1, my bench amp, SD702
and a number of different video-cameras.
Klas.
>Regards,
>Raimund
>
>http://www.avisoft.com
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
website: www.telinga.com
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