Nothing drives pin 2. It is signal grounded to +. Its source
impedance is given by the HF coil in series with the output.
Pin 3 gets the signal from T3, T4. The output impedance is only a few
ohms, which means that pin 3 also will have the same impedance as pin
2, that is the HF coil.
That the signal is on pin 3, instead of pin 2, is only a matter of
taste, really.
The "fluent ground" at the collector of T6 is a consequence of that
the voltage stabilizer (38v - 28v =3D 10v for the output stage) is put
in series with the rail. That is smart, as the stabilizer - this way
- doesn't need any current, as if it was connected from + to ground.
The fluent ground has nothing to do with any symmetrical output.
Pin 3 carries a signal, Pin 2 does not =3D balanced, but unsymmetrical.
Klas.
At 14:48 2007-03-22, you wrote:
>pin 3 is driven by the two transistor circuit, but what drives pin
>2? it is connected with a 22 mfd cap to positive. the positive
>supply of course is effectively at ground.
>
>the early mkh series, 405s and 805s had a common emitter driving
>each pin, but the later circuits went the impedance balancing route.
>the early circuits did not have a signal on both pins either. i
>think only the transformer output microphones are truly balanced.
>
>
>
>umashankar
>
>
>----- Original Message ----
>From: Raimund Specht <>
>To:
>Sent: Thursday, March 22, 2007 1:53:50 PM
>Subject: Re: [Nature Recordists] Phantom power noise - again!!!
>
>
>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
>
>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. 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!
>
>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
>
>
>
>
>
>__________________________________________________________________________=
>Don't pick lemons.
>See all the new 2007 cars at Yahoo! Autos.
>http://autos.yahoo.com/new_cars.html
>
>
>
>
>"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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