Hi Oryoki--
Very interesting results Oryoki. I've also heard that David Dunn
reports having very good results with impedance matching
(transformers?) on PIP inputs. Debate about this has circled around
with no clear conclusions for years.
The reading I've done is of mixed opinion but most conclude that
a150-600 ohm mic _should_ perform up to spec when the recorder's
input impedance is ~ 2000 ohms (which I have read is a good estimate
for most PIP grade recorders, but that might need to be
researched/measured too). Since you are getting such a pronounced
gain change, I think a test is definitely in order. I've ordered an
A96F unit and will get back to you about the specifics of your set-up
before running it. There's a setting on the unit for 150 ohm mics,
for example.
The pdf owners sheet for the A96F Shure transformer is:
http://www.shure.com/ProAudio/Products/Accessories/us_pro_a96f_ug for
anyone who would like to explain and discuss Oryoki's performance
difference.
Oryoki, if you get a chance, maybe you could post short 44.1K/16
sound files with and without the A96F? Middle of the night room tone
at max record gain should show all the warts and advantages of the
extra gain and reveal any change in tonal balance on the low end. If
you run the recorder for 10 minutes for each test and then pick the
quietest 5 seconds from each waveform, that's usually provides a very
similar source match.
It would be great to have some solid info established about the
affects of impedance matching at least with some specific mic/Hi-MD
combinations that people can judge for themselves. I'm curious, for
example, if a transformer pair could produce similar gain increases
following a Rolls or Art and thus enable more saturation when
recording ambience in quiet locations with any condenser mics, not
just self-powered ones. In cases when DC blocking of the PIP circuit
is needed, (as with some older camcorders and recorders I tested)
Shure's adapter seems to provide this as well.
I am an "ears-first" audio technician as well. If folks with much
more audio engineering expertise can point to variables to factor in,
your help would be much appreciated. Rob D.
= = = = =
At 5:54 AM +0000 6/10/06, oryoki2000 wrote:
>I have read conflicting points of view about impedance matching:
>
>1. Matching the impedance of the mic output to that of the recorder
>input reduces the power lost when a signal is transmitted. The result
>is a louder recording without needing to boost the signal through the
>recorder's preamp. For a brief discussion, see:
>
>http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html#c4
>
>2. Modern transistor designs (meaning any audio device made since the
>1980's) use voltage transfer rather than power transfer. Voltage
>transfer is actually improved when there is a large difference in
>impedance between mic and recorder. So matching impedance will reduce
>the volume of a recording.
>
>http://www.shure.com/ProAudio/Products/us_pro_ea_imepdance
>
>
>Perhaps these two points of view are not mutually exclusive. I have
>little understanding of the physics and electrical engineering
>principles involved here. In my limited experience, however, I find
>impedance matching to be a valuable way to gain some volume without
>adding extra preamp noise.
>
>The impedance of my Sennheiser ME62 is 200 ohms. The impedance of a
>Sony minidisc recorder is about 2000? 5000? ohms. (If I remember
>correctly, Sharp minidiscs have a mic input with 10,000 ohm
>impedance.) When I use a Shure A96f impedance matching transformer
>($40) to raise the ME62 output to 2500 ohms, the minidisc records a
>considerably louder signal.
>
>A member of this list had similar results by employing the Hosa
>MIT-156 impedance transformer ($20). This device is also calibrated
>for 600 ohm mic output and 2500 ohm recorder input.
>
>Both cables have the added advantage of having an XLR female connector
>on the mic end, and a 3.5mm male connector on the recorder end. So
>either cable will let me connect a pro mic to the minidisc recorder.
>
>--oryoki
>
>
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Peck School of the Arts
University of Wisconsin-Milwaukee
http://www.uwm.edu/~type/audio-art-tech-gallery/
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