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Old 18th September 2006, 08:37 AM   #1
AdamZuf is offline AdamZuf  United Kingdom
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Question Stereo binaural WM-61A with preamps

Hello,
I'm interested in building a pair of binaural microphones, and use a dummy head.
First, I don't know much about electricity, I just do possible simple stuff from time to time, so talk simple to me, guys.

I assume that the weakest part of cheap recorders (MD's or HD recorders) are the preamps. So, it's logical to push the mics to line level, and adjust the proper output impedance. Many recorders have line input but not all of them got line input.

Looking at Linkwitz's design (is this guy thrustworthy or what?) :
http://www.linkwitzlab.com/sys_test.htm#Mic
Do you guys think that it's a good base for a stereo schematic?
How should this simple preamp compare to the ones found in sub $400 recorders? (and even the new Sony Hi-MD's?)

If so, what will happen if I share these batteries with the second mic? What should I change in this schematic if I want to add the second mic?

There's also Rod Elliot's version (look at the one with the preamp):
http://sound.westhost.com/project112.htm
I don't have the slightest idea what would be better (-:


By the way, where's a good place to buy these Panasonics that also has a large selection of electronic parts? (Like Mouser, bt they don't have them)

Thanks
Adam
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Old 18th September 2006, 09:29 AM   #2
lineup is offline lineup  Sweden
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hi

I have a couple of National Panasonic WM-034 at home.
Very good electret microphones in relation to low price!

WM-61A is even better, and to prefer, what they say.
But I took what could find.

At this panasonic page you can download PDF Datasheets for your microphone WM-61
http://www.panasonic.com/industrial/...io/aud_mic.htm
Yours:
http://www.panasonic.com/industrial/...61_a_b_dne.pdf
Here is mine, WM-034:
http://www.panasonic.com/industrial/...db_c_d_dne.pdf

WM-61
Click the image to open in full size.
WM-034
Click the image to open in full size.

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Old 18th September 2006, 02:50 PM   #3
protos is offline protos  Greece
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Linkwitz and Elliot are extremely respectable and anything on their sites is well thought out.
The mod on the pana mic is necessary but may be a little bit tricky if you have no soldering experience.They mikes are very cheap and you can buy a dozen if you can find some in small quantities to experiment.A preamp may not be necessary depending on recording levels and gain of MD.Otherwise quality can be very very good although personally I found that playing thru speakers needs some bass eq cut.
Ideally you should try and match the two stereo mikes for close output levels so getting some extra mikes is always a good idea.
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Old 18th September 2006, 03:18 PM   #4
soongsc is offline soongsc  Taiwan
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Linkwitz site also has a design with the mics on a pair of eye glasses.
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Old 18th September 2006, 06:38 PM   #5
AdamZuf is offline AdamZuf  United Kingdom
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Quote:
Originally posted by protos
A preamp may not be necessary depending on recording levels and gain of MD.
So, looking at Linkwitz's stereo schematic, what will be the output impedance?
IIRC, the optimal ratio between output and input impedance is about 1/10. Is that correct?

Thanks!
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Old 18th September 2006, 07:15 PM   #6
paulb is offline paulb  Canada
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I used an INA217 with the WM-61. It's just based on the datasheet at www.ti.com. Simplest solution for best performance. I can change the gain by plugging in different resistors into a DIP socket.
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Old 18th September 2006, 08:09 PM   #7
lineup is offline lineup  Sweden
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Quote:
Originally posted by paulb
I used an INA217 with the WM-61.
It's just based on the datasheet at www.ti.com.
Simplest solution for best performance.
I can change the gain by plugging in different resistors into a DIP socket.
Thanks for the Burr-Brown / Texas INA217 info, paulb
( This is a replacement of much used and good SM2017 mic amp IC )

Here a very nice project using this INA217 ( SM2017 )
with 2 High quality LM833 OP-amps for the output.
Included many schematics and pictures!

KDMP - Kev's Dual Mic Pre in a rack box
http://www.celestial.com.au/~rosswood/diy/KDMP/kdmp.htm

Click the image to open in full size.

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Old 26th December 2006, 09:47 AM   #8
AdamZuf is offline AdamZuf  United Kingdom
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Well, I've decided that my player with be the Sony MZ-NH600.
It's a HI-MD player that works on AA. Only line ins. However, I don't know if it's possible (or easy) to change recording levels from it on the fly.

I want the rig to be very portable, So it's either Elliot or Linkwitz's design.
As the discussed circuits are all quite small, quality is the first thing to consider. OTOH, I hope I won't have to carry more then 2 9V batteries in this pack (and get reasonable battery life).

But I still didn't get a straight answer from anyone about what input level and impedance should the line in section in the MD player "see" , considering that it's the modded capsule used.
Linkwitz staits the specs of the WM-61A's capsule and his circuit but honestly I don't really understand it, translate it to my needs, and choose one of his circuits, or maybe Rod's.
Let's reorder things:

Linkwitz's single channel 10dB preamp version (/w WM-60AY)
Click the image to open in full size.
Quote:
A more sensitive capsule with a few dB lower noise of 26 dB(A) is the WM-61A. It outputs a maximum 5 Vpp at about 134 dB SPL.
Linkwitz's dual channel (no preamp)
Click the image to open in full size.
Quote:
The wiring diagram for a stereo microphone with output attenuator, if needed, and using the modified capsules is shown on the microph2.gif page. Attenuation of the microphone output degrades the signal to noise ratio and should only be used, when the preamplifier gain can not be reduced.
Elliot's P112, with the electret capsule mod preceding it
Click the image to open in full size.

Click the image to open in full size.
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Old 26th December 2006, 02:56 PM   #9
soongsc is offline soongsc  Taiwan
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One Sony MD that I have used before, I did not even need a preamp or battery. It supplied aournd 2.5V phanton power. All I had to do was hook the panasonic capsules into the MD using a 3.5mm earphone plug. I actually moded a set of earphones and used that. The MD I used allow changing volume level on the fly. One thing though is that the recording was polarity inverted. For best results, it needs to be inverted back during playback.

Quote:
Originally posted by AdamZuf
Well, I've decided that my player with be the Sony MZ-NH600.
It's a HI-MD player that works on AA. Only line ins. However, I don't know if it's possible (or easy) to change recording levels from it on the fly.

I want the rig to be very portable, So it's either Elliot or Linkwitz's design.
As the discussed circuits are all quite small, quality is the first thing to consider. OTOH, I hope I won't have to carry more then 2 9V batteries in this pack (and get reasonable battery life).

But I still didn't get a straight answer from anyone about what input level and impedance should the line in section in the MD player "see" , considering that it's the modded capsule used.
Linkwitz staits the specs of the WM-61A's capsule and his circuit but honestly I don't really understand it, translate it to my needs, and choose one of his circuits, or maybe Rod's.
Let's reorder things:

Linkwitz's single channel 10dB preamp version (/w WM-60AY)
Click the image to open in full size.


Linkwitz's dual channel (no preamp)
Click the image to open in full size.


Elliot's P112, with the electret capsule mod preceding it
Click the image to open in full size.

Click the image to open in full size.
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Old 26th December 2006, 03:38 PM   #10
lineup is offline lineup  Sweden
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Cool WM-61A Panasonic elektret microphone capsule Linkwitz

hi

Linkwitz used WM-60A
in his first set up, as seen in his schematics
with modified elektret input-JFET mic transistor circuit.

As told by previous poster here
WM-61A can be used to replace with improved performance.
somewhat higher sound sensitivity and lower noise
-----------------------------------------------------------------------------

For those in northern Europe,
who would want to try the very good (performance/price)
Mic capsule Panasonic WM-61A
.... we have a supplier here
Click the image to open in full size.
Quote:
WM-61A is slightly more sensitive and has slightly lower noise.

It's also Mr Linkwitz who has made the amusing stereo microphone glasses to the right.
You use your own head as a "dummy head" during recording or measurements :-)
http://www.svalanderaudio.com/shoppen/mik.php
Prices: (I think maybe you can find lower price at some bigger electronics suppliers)
For delivery inside EU
1-4 pcs WM-61A EUR 6.94
5-9 pcs WM-61A EUR 5.76
10+ pcsWM-61A EUR 4.59


StartPage http://www.svalanderaudio.com/

Some good stuff for Vinyl Turntables
.. like extremely good Cartridges Nagaoka ! Ortofon etc. and other fancy Vinyl Accessoires.
VinylPage-Shop: http://www.svalanderaudio.com/vinyl/vinyleng.php


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