Well,
Motivated by several requests for follow-up on this in the past several
days, I put down my 12-week-old daughter for a while today, and tried
various combinations of plug-in powered mics, my Sound Devices 722, and thi=
s
cable:
http://www.soundprofessionals.com/cgi-bin/gold/item/SP-XLRM-MINI-2
It looked very promising, being not only a 1/8" stereo miniplug to dual XLR
male adapter, but also a phantom power to plug-in power adapter as well.
With no "box," just a normal looking cable, I had high hopes that this was
simplify my kit when using mics that require plug-in power.
Sadly, my results so far are not encouraging -- though there is a caveat,
which is that what I am hearing may result in most part from the Sound
Devices front end's behavior when it is presented with what I assume is not
a balanced input while it is in "Mic" mode. I have reason to suspect this
(though that doesn't help me in my case).
I tried the test cable with a pair of Microphone Madness phantom-powered
cardioid mics on a gooseneck, which I believe are based on Sennheiser MKE
capsules; a pair of the venerable Radio Shack 33-3028 stereo lav mics; and
my go-to mics, my Sonic Studios DSM-6S/EHs, with and without the expensive
Sonic Studios matched preamp in series.
I traded some email with the SP folks when ordering, and they said that it
should present about 9-10V to the mics as I recall. Being familiar with the
warning of Leonard Lombardo (Sonic Studio) on what his mics require in a
Plug-in Power source -- "high current capacity but not high voltages" -- I
also confirmed that the adapter would be able to supply said current. (I
also tested my less dear mics with the cable first, lest their be any risk
that it passed too high a voltage!)
Both the MM goosenecks mics and the Sonic Studios mics (direct) had poor
results when powered through the cable -- at least, into the input on the
Sound Devices when set on "microphone." There was a distracting degree of
noise that I am not used to, and what I can best describe as a "fluttery"
couple-hertz irregular mid-low frequency beating. I would almost call it
"stuttering" and though I don't think it's related to the use of this term
for mics tapping out the MP-2, I in my own tests described it as "motor
boating." In addition, my beloved DSMs in particular did not seem to be
performing to the standard I am use to; their output was quite low. Combine=
d
with the high noise I would call the combination unusable.
The 33-3028s worked better out of the gate, but at high gain I could still
detect the same "fluttering" happening; for some reason though they did
perform better than either of the other pairs of mics -- enough that a
casual use might not have revealed the fluttering right away. Perhaps they
are the "happiest" with the high voltage / low current (?) provided by the
cable?
What makes me suspect that the problem is partly a result of the Sound
Devices' input [topology] is that the noise I am hearing is quite similar t=
o
the large amount of noise you get if you turn on the microphone inputs with
no mic [load] attached -- I would wager in fact that what I am hearing is
the *same* noise. I'm not an EE but I immediately suspected that the proble=
m
may be that the SD is really expecting a balanced input and or the correct
impedance?
I actually have encountered a similar issue before, using a Sound
Professionals dedicated plug-in power box to power my electret Aquarian H2
hydrophone, and then breaking out to XLR into the 722... lots of noise. Too
much to use this combination.
Sometime soon I may repeat this test using my venerable Mackie 1202 VLZ as
the phantom source -- just to see if its presumably quite different inputs
work with the cable any better.
As a sanity check, I also powered my DSMs through their dedicated Sonic
Studios preamp, which both (perfectly) power and amplifies them, and used a
standard break out cable to dual XLR to connect them to the 722 when in
"Line" input mode. This case -- which I have used before -- works well; the
only limitation being that only 18 db of (additional) gain are available
from the 722 -- I would appreciate a bit more, even on top of the gain
provided by the Sonic Studios pre. In this configuration the limiting noise
floor seems to definitely be the mics, regardless, though; I get much, much
better results than with the tested cable.
Last fall I also used this combination -- DSMs -> Sonic Studios pre ->
standard breakout cable -> 722 -- into the 722's input in *microphone* mode=
;
I encountered what I now believe based on these experiments is possibly the
same issue. I should look in the 722 manual to see if flipping that switch,
in addition to offering more gain, changes the impedance on the input as I
suspect...
My goal btw was to use my DSMs directly with the 722, without the
intermediate pre. The latter is very small -- think, a pager -- but it's on=
e
more box to wrangle, and I do sometimes forget to shut it off and hence bur=
n
down the (very long lasting) AA in it.
I can say that for the moment, though, that I will continue to use the Soni=
c
Studios sanctified powering options.
Question for the EEs in the group ~ is it possible that there is some simpl=
e
modification to the cable that might alleviate what I am hearing? Or would
we need to dissect the cable to see what's really going on and why the 722
is unimpressed with this as in input? I know where we can get one. :)
best,
aaron
--
quietamerican.org
oneminutevacation.org
83% happy
9% disgusted
6% fearful
2% angry
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause
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