Thanks for posting your tests, Dan. I just got my 183s wired direct
to p-i-p, with an adapter cable I made to get from two TA4Ms to mini.
Subjective quality and noise performance is impressive going direct
to the MD. (sony MZ-R37) I attribute this to the high sensitivity
and output of the mics. I'm keeping the gain in the middle of its
range and getting good levels, whereas with other mics I'm always
pushing to top of the preamp range to get the same levels. This is
encouraging, as it means smaller, simpler kit.
I also tried with the Shure MX phantom power modules, via Grace
Lunatec preamp, to the same MD recorder. Similar subjective results
to Dan: a higher percieved noise floor in the high mid to high
frequencies.
Dan: why not set up a simple battery-powered test, powering the 183s
via a 9-volt or series of AAs, to test the efficacy of going direct
into a pro mic pre? Could that answer some questions, like impedance
issues, prior to building a custom circuit? I'm not an electronics
engineer and there may be issues I don't understand here, but it's a
thought.
-j
>Dear Colleagues,
>
>Today I set up a comparison of ways of connecting the 183 mics. They
>call them preamps, and they do have a little gain, but I'm going to
>call them power modules to avoid confusion with the mic preamps that
>they have to be used with.
>
>The MX power module can be ordered separately as the MX183PK. The
>battery module can be ordered as the MX1BP.
>
>For my first test I compared my Sharp MD-MT90 recorder with the Shure
>MX183 phantom powered module. I put two 183 mics next to each other
>on the bench, and viewed the results on a Macintosh "Spectrafoo" FFT
>spectrum analyzer. All my tests were comparisons, there were no
>absolute measurements. I swapped the mics to make sure I wasn't
>looking at differences between the two mics. They matched within
>about 1 dB.
>
>Test 1:
>
>Left: WR183 -> Sharp MD-MT90 gain MIC L 20, phones level 30, phones
>output -> Sound Devices USBPre line input L, gain max.
>
>Right: MX183 (gain jumper +12) -> Sound Devices USBPre mic input
>(48V), gain knob 1:00.
>
>I looked at room ambience, which had a lot of low frequencies since
>I'm near a freeway. Gain controls when set as above matched the
>spectra exactly in the range 200 Hz - 1 KHz.
>
>Observations:
>
>Low end: below 60 Hz the Shure MX module starts rolling off a little.
>It's about 3dB lower than the Sharp at 30 Hz, 5 dB at 16 Hz.
>
>Treble: the Shure module showed an approximately 2 dB depression
>between 2 KHz and 8 KHz, followed by a rise at the high end, up about
>5 dB at 18 K. I suspect the hf rise was noise mixing with the
>ambience.
>
>Test 2:
>
>Same wiring setup, with a pile of pillows on the mics. This damped
>out the ambience above around 1 KHz so I could see the high-frequency
>noise level.
>
>Observations:
>
>The 2 KHz - 8 KHz depression disappeared. The MX183 preamp had more
>noise than the Sharp, starting from about 2 KHz, to +3 dB at the top
>end.
>
>Test 3:
>
>Same wiring setup. Changed the gain jumpers in the MX preamp to 0 dB.
>Brought up the gain at the USBPre input to match the Sharp.
>
>Observations:
>
>The high frequency noise stayed about the same, with a 1 dB midrange
>rise between 500 Hz and 2 KHz. Couldn't tell if that was a change in
>noise or a change in frequency response.
>
>Test 4:
>
>Instead of using the USBPre mic input, I changed to a Sound Devices
>MP-2, feeding balanced to the USBPre's right line input. The MP-2
>gain was 12:00.
>
>Observations:
>
>No change. Since the MP-2 is supposed to be a little quieter than the
>USBPre, this indicates the preamp noise probably isn't dominant in
>this situation.
>
>Test 5:
>
>Keeping the MP-2, I substituted the Shure battery pack version, the
>MX183BP, without battery (using phantom). The output was about 7 dB
>lower, so I raised the MP-2 gain to around 2:00 to match it to the
>Sharp again.
>
>Observations:
>
>The HF noise was higher, up from the Sharp about 1.5 dB at 8 KHz, and
>+4 dB at 16K. The extreme low frequency response came up several dB,
>however, higher than either the Shure MX or the Sharp.
>
>Conclusions:
>
>The noise level of the Shure 183 mics with good preamps is determined
>by the mics and their power modules. No improvement should be
>expected with expensive preamps.
>
>The mics were the quietest on the cheap little preamps in the Sharp
>MD recorder! The noise (hiss) is about 3 dB higher at the top end
>with the MX power module and a pro preamp, and an additional dB
>higher than that with the BP power module.
>
>I'm thinking about tearing apart the BP preamps and kluging together
>a phantom supply that just turns phantom into p-i-p, and passes the 3
>Kohm impedance mic signal right through. Whether this is too high a
>source impedance for professional inputs remains to be seen.
>
>-Dan Dugan
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
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jeremiah lyman moore | sound+media | san francisco |
http://babyjane.com/timeweb/
http://northstation.net/ downtempo acid jazz project
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