[Top] [All Lists]

6. Re: R-44 issue-geek reply

Subject: 6. Re: R-44 issue-geek reply
From: "Jez" tempjez
Date: Sun Jun 24, 2012 1:11 pm ((PDT))
Hi Raimund,

perhaps, at least to answer some of the frustration & puzzlement about this=
 issue, could you let us all know if any other recorders at the pro-sumer o=
r entry level have the same kind of issues & more to the point perhaps, why=
 even if they do they appear to be able to handle the DPA's ok ? thats the =
bit I can't get my head round.

--- In  "Raimund" <> wrot=
> > Hi Raimund, this is indeed a very telling test, but the the imbalance i=
s not as much as you perhaps think. i.e. by leaving the 150R across the pin=
s, from the 48V you have 6K8 to the 2k2 direct and 6K95 to the 2K2 via the =
Message: 150R. 
Subject: i.e. a 2.2 percent imbalance.
> Agreed, Rob.
> > And its supposed to be a pure DC, not contaminated with system noise!
> Sure, but it is often a challenge to generate such a perfectly pure DC vo=
ltage out of a low battery voltage.
> > Anyway, the point I take issue with is the "poorly designed (unbalanced=
) microphone". The only poor design appears to be the R44 phantom supply, e=
ither a poor return path, poor decoupling or both.
> I beg to differ here! The phantom power specification demands perfectly b=
alanced currents on both rails. For that reason, the two internal 6.8 k res=
istors must be matched to within at least 0.4% (see
/wiki/Phantom_power). The microphone itself should therefore also be perfec=
tly balanced. Otherwise, the matched 6.8 k resistors within the recorder wo=
uld be meaningless.
> > In principle there is absolutely no reason why one couldn't short eithe=
r of the two signal pins to ground, save that the common mode rejection wou=
ld of course negated.
> Hmmm, I'm not sure if that would be a good idea, given that it is quite d=
ifficult to design a perfectly ripple-free phantom power supply.
> Raimund

<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU