I have a possible application of "attenuation on purpose" I'd like to sugge=
st.
Thanks to Allan Haighton of the HiMD Forum, I'm looking into the
nature of small circuit built into the unbalanced, 3.5mm cable that
Rode provides with the NT-4. I've by-passed the circuit in my NT-4
cable and mic output jumped up 12dB-- the same dB drop in output (and
increase in noise) that I was trying to account for in the tests a
few months back. I was wondering what the circuit is and why it would
be there if not to protect the mic pre circuit. Maybe its a music
recording assumption? If so, its not very compatible with recording
in quiet places or even moderately noisy situations.
I'm waiting to recommend the simple cable modification until I can
figure out if there are bad consequences I've not grasped. Here's
what I think** the circuit is should anyone have ideas:
http://www.uwm.edu/~type/Mic%20Preamps/NT-4ConnectorCircuit&ModSm.jpg
Its a small pcb attached to contacts on the xlr-5 connector.
I'd like to know about significant risks myself because I'd like to
make the mod to all of our cables before the semester begins.
**umashankar mantravadi, who is on this list, has commented on the
micbuilders list that my circuit drawing looks more like line to mic
pad, which, I assume, would have much greater attentuation than
-12dB. Maybe the four tiny components on the pcb are not simple 10K
resistors, as labeled and measured? I dunno. I think I have the basic
circuit structure right though. Rob D.
=3D =3D =3D =3D
At 1:20 PM +0200 9/3/05, Klas Strandberg wrote:
>A part fell out from my posting:
>
>One must remember that microphone manufacturers might keep down their
>output voltage on purpose, not to distort the input amp of a consumer MD,
>if you record at a pop concert or blow the trumpet into the microphone.
>Therefore, a consumer microphone may very well be very good, - for general
>purposes - but doesn't fit the naturesound recordist, as the output is too
>low to override the consumer MD input noise.
>
>Klas.
>
>At 17:41 2005-09-01, you wrote:
>>Do you think we'll be able to get a sensitivity number or even an
>>accurate range of mV/Pa : dbB(A) combinations that will apply to
>>DAT/MD/HiMD mic preamp's in general? I tested the Rode NT-1A's with
>>the Rolls phantom power supply with these recorders:
>>
>>NH900 HiMD
>>Sharp MT-90
>>Sony D-7
>>Sony TRV-900 (video camcorder)
>>
>>and found that the NH-900 is significantly quieter than the other
>>recorders with the Sharp MD being the noisiest.
>
>
>That doesn't surprise me. Sharp got some stupid ideas from last years
>models, the input PIP current regulator, for one.
>
> From my perspective: Many customers use a "Walkman" type MD. Sharps, too=
.
>I want to provide a microphone which output is high enough to override the
>input noise of such a machine.
>All Telinga mic's (without dish, of course) make about 14 db(A) noise. Wit=
h
>the capsules I use, and the FET-IC's I use, this comes free. Without any
>complicated circuitry, all Telingas override the input noise of even a las=
t
>years Sharp. I know that, because I use the poor Sharp machines as "minimu=
m
>reference".
>
>But when people here are choosing other mic's, I think there would be at
>least some reference, at least referring to the NH900.
>
>That is: If you use a NH900 - then you can use any electret providing more
>than xx mV/Pa with a self noise lower than 14 db(A). If you do, you don't
>have to worry about the NH900 input noise. The noise you get, is from the
>electret.
>
>Or vice versa: If you use a Sharp MT-90 - then a 14db(A) microphone must
>provide at least yy mV/Pa to override the Sharp input noise.
>
>Klas.
>
>
>
>
>
>
>
>
>
>>I've been thinking about the min mV/Pa question since you posed it a
>>while ago. I came across table #3 on
>>http://www.rane.com/note148.html. With this chart, it seems like we
>>might be able to take what we know about the NH900 performance to
>>estimate the noise floor of NH900 mic pre for starters. I'm pretty
> >confident that the noises I'm hearing when I hook up:
>>NT1A->Rolls->NH-900 are close to a 50-50 blend of mic and NH900 mic
>>preamps. Applying the NT1A's specs* to table #3, I get ~-118 dBu for
>>the NH900 HiMD mic pre, but I'm blindly following the chart and other
>>aspects of the chart confuse me. Rob D.
>>*6dB(A); 25mV/Pa
>>
>> =3D =3D =3D =3D =3D
>>
>>At 11:34 AM +0200 9/1/05, Klas Strandberg wrote:
>> >With only 5,6 mV / Pa I am certain that you get MD preamp noise.
>> >You need too much gain.
>> >
>> >That is what I would like to discover: At which output / Pa does a typ=
ical
>> >MD preamp noise "take over".
>> >
>> >Klas.
>> >
>> >At 04:44 2005-09-01, you wrote:
>> >>At 5:07 PM -0700 8/31/05, Dan Dugan wrote:
>> >> >Lou Judson wrote:
>> >> >
>> >> >>Curiosity took me to the Soundprofessionlas website this
>>morning, and I
>> >> >>see they have some closeouts on their stereo pairs already wired =
for
>> >> >>PIP - $49 instead of 129. Has anyone compared theirs to such as t=
he
>> >> >>Shure 183s? Ths ones on sale now are cardioid, yet for some of wh=
at I
>> >> >>do they would be ideal.
>> >> >>
>> >> >>http://www.soundprofessionals.com/cgi-bin/gold/item/SP-CMC-22
>> >> >
>> >> >It was Sound Professionals who turned me on to the 183s, just befo=
re
>> >> >they changed to something else.
>> >> >
>> >> >Sharon Perry uses SP cardioids, which are Audio-Technicas, for her
>> >> >vest. Gain is about the same as 183s, but the cables are quite
>> >> >microphonic. Don't know if that's the type they're currently using=
.
>> >> >
>> >> >If the s/n of "58" is correct, 94-58 =3D 36dB, pretty high.
>> >>
>> >>and a (lower) sensitivity of 5.6mV/Pa (high mV/Pa #
>> >>[sensitivity.output] is good; low dB(A) # [self noise] is good.)
>> >>
>> >>compare to:
>> >>Panasonic WM61a capsule 32.5 dB(A)* 18 mV/Pa **
>> >>spec sheet: http://tinyurl.com/8g4l9
>> >>Cost $16.21 for 10 + shipppiing http://www.digikey.com/ and enter
>> >>"wm-61a" into parts search.
>> >>You can solder a workable set to run on MD/HiMD plug in power for a
>> >>few bucks more http://webpages.charter.net/tidmarsh/binmic/
>> >>
>> >>*Based on Eric B's test on file on the micbuilders list.
>> >>http://tinyurl.com/8tkt4 **Is this sensitivity number right? Eric's
>> >>test seems to confirm Panasonic's figure of (0dB=3D1V/Pa, 1kHz)
>> >>-35+/-4dB.
>> >>I need to learn how to make this conversion.
>> >>
>> >>and for reference:
>> >>ShureWL-183 22 dB(A) 29 mV/Pa
>> > >Rob D.
>> > >
>> >
>> >Telinga Microphones, Botarbo,
>> >S-748 96 Tobo, Sweden.
>> >Phone & fax int + 295 310 01
>> >email:
>> >
>> >
>>
>>
>>[Non-text portions of this message have been removed]
>>
>>
>>
>>
>>"Microphones are not ears,
>>Loudspeakers are not birds,
>>A listening room is not nature."
>>Klas Strandberg
>>Yahoo! Groups Links
>>
>>
>>
>>
>
>Telinga Microphones, Botarbo,
>S-748 96 Tobo, Sweden.
>Phone & fax int + 295 310 01
>email:
>
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
[Non-text portions of this message have been removed]
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