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Re: Hi-MD Input Clipping (was Sony HiMD questions

Subject: Re: Hi-MD Input Clipping (was Sony HiMD questions
From: "Rob Danielson" danielson_rob
Date: Thu Jul 13, 2006 12:43 am (PDT)
At 9:09 PM +0000 7/12/06, stoatwizard wrote:
>  > The Hi-MD mic pre in Hi sens should be able to handle this level
>>  without distortion (although ECM mics, in general, have lower SPL
>>  maximums).
>It may not be the HiMD mic pre clipping. Something that is pretty
>sick about my HiMD NH700 is the gutless plug-in-power capability. The
>PIP measures an acceptable 2.3V open circuit, but when I plug my
>OKMII binaurals the votage available to the mic drops to a lousy 0.7V
>on one side and 0.4V on the other. Which is a bit crap IMHO, so I got
>to poking around to find out what is going down. The short-circuit
>current is 340uA, which isn't enough to get many electrets going. I
>have two of these MD recorders, and both measure the same. This
>implies the tail resistor is 6k8 which is waaaay too big for such a
>low voltage. The result is the electret mic is being starved for
>drive current, and there is not enough voltage across the FET for an
>output of much above 0.2Vp-p. Which is why the signal disappears in
>wind blast for example.
>Starving the mic for current and FET voltage isn't going to do
>wonders for its sensitivity, headroom, linearity or noise
>performance. The solution is cheap and easy, though a right pain in
>the field. Use a battery box - it's a 9V PP3 battery, two stereo
>sockets, a couple of 6k8 resistors and two 100uF caps. That way
>you'll get about 4V across you mic, and gain headroom and some
>sensitivity (electrets seem to go low gain at FET voltages < 1V)

Richard, your comments are very useful together with Graham's Low
Sens observation. By chance in helping student record a lute tonight
with Panasonic WM61A's, I found that the Low Sensitivity setting did
prevent distortion. (I'd never tested it because I assumed it was a
pad). Could there be unique, insufficient power PIP problem with ECM
mics that makes the Sony's clipping vulnerability at High Sen much
more pronounced? I've recorded numerous thunderstorms, wood chopping,
ice cracks etc with condenser mics>Rolls-> without the
distortion. An A/B comparison of with and without your battery box
could provide clues. I saw the one you made for the 35-1090's. Rob D.


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