Thanks much for these time-consuming/telling tests. I was holding
onto hope, but it does make sense that a pro mic preamp wouldn't help
a mic with ~21dBA self noise and high sensitivity like the 183 has.
PIP out-shinning Shure's MX power supply is a shocker. A phantom->PIP
power module is a humorous twist. I assume there's no way the 183's
FET could be hacked for balanced/power. I'm curious about about a
couple of things:
>
>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.
Does this introduce the MT-90's headphone amp performance into the
Left channel?
Would you say that the combined low noise/high output of the Shure
mic is primarily responsible for the Sharp MT-90's internal mic
preamp being a non factor in your test? Folks who read your
conclusion who are using a much lower output mic like the MS-957 or
even the Rode NT-4 (which I found to be on the order of ~18dB less
output than the 183's) might think the MD pre isn't adding noise when
they crank the mic pre gain to make-up for the lower output.
Rob D.
=3D =3D =3D =3D
At 11:49 PM -0800 1/7/05, Dan Dugan wrote:
>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
>
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