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1. Re: Phantom power noise - again!!!

Subject: 1. Re: Phantom power noise - again!!!
From: "umashankar" umashanks
Date: Thu Mar 22, 2007 6:56 am ((PDT))
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 circui=
ts 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
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