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Old 9th November 2005, 04:21 PM   #1
djkib is offline djkib  United States
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Location: Coatesville, PA, USA
Default Input Level Matching?

To all,
Sorry for the length, but I wanted to include all the details in the first post...

I posted here because I could not figure out which would be the correct forum...

I have a Yamaha MV802 mixer that has 8 input channels and two output channels. I would like to use this mixer to mix 8 microphone inputs to stereo output (the device does have the stereo output part). However, the first two channels are the only channels that are switchable between "MIC LEVEL" and "LINE LEVEL". Additionally, each channel has a "PAD" switch that seems to change the sensitivity by 29dB

The input specs for the amp are:
Ch 1-2: MIC Mode: PAD OFF:
Input Impedence: 10K Ohms
Source Impedence: 150-600 Ohms
Sensitivity (Max. Gain): -62dB (0.62mv)
Input level: Rated: -50db (2.5mv) Max. Non-Clip: -23db(55mv)
Ch 1-2: MIC Mode: PAD ON:
Input Impedence: 10K Ohms
Source Impedence: 150-600 Ohms
Sensitivity (Max. Gain): -55dB (1.4mv)
Input level: Rated: -43db (5.5mv) Max. Non-Clip: -16db(123mv)

Ch 1-8: LINE MODE: PAD OFF:
Input Impedence: 10K Ohms
Source Impedence: 600 Ohms
Sensitivity (Max. Gain): -32dB (19mv)
Input level: Rated: -20db (78mv) Max. Non-Clip: +7db(1.74v)
Ch 1-8: LINE MODE: PAD ON:
Input Impedence: 10K Ohms
Source Impedence: 600 Ohms
Sensitivity (Max. Gain): -12dB (195mv)
Input level: Rated: 0db (775mv) Max. Non-Clip: +20db(7/75v)

I have attached the users manual in case someone wants to see...

Can an "adaptor" be created designed that will take the mic output and convert to line level? I only need to drive one side of the stereo line level input on this mixer...

My intention is to create a rack mounted amp system to amplify various marimbas vibraphones and other mallet instruments during indoor percussion competitions. Mics are wireless, mounted to the instruments, everything else will be mounted in a rolling rack for quick setup/teardown.

Thanks for your expertise,
Keith Kibler
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Old 9th November 2005, 09:23 PM   #2
Optical is offline Optical  New Zealand
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The short answer is that you will need a further 6 mic preamps to get a quality signal. For the cost of the preamps you would probably be better off getting a new mixer with more mic preamps.
You could build them much much cheaper than it would cost to buy them however.

the line level signal is much louder than a mic level signal, and also the impeadences are different. so the mic premap would fit between the mic and the mixer line input.

alternatively since you are using wireless mics, does the reciever have a line output?
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Old 9th November 2005, 10:09 PM   #3
djkib is offline djkib  United States
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That is exactly my thought... build 6 more mic pre-amps...

I have not, however, found a design that would satisfy my needs, and raise the mic output to somewhere near the voltage? needed to satify the line input.

I did check out <ESP Low Noise Microphone Preamp> , but not sure how many amps at 30V I need for 6 more pre-amps, and building a 30V power supply that is "smooth" as Mr. Elliot suggests is probably beyond my budget...

Anyway, thanks for the pointers!

Peace,
Keith
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Old 10th November 2005, 02:00 AM   #4
Optical is offline Optical  New Zealand
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you would require much less than an amp to run 6 mic preamps i imagine, hardly any power at all.. maybe 100mA max per opamp, much less for a transistor, so you can just add it up..

a power supply can be made very cheaply also, a few RC circuits in series after a voltage regulator will easily lower the noise adequatly..
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Old 11th November 2005, 04:27 AM   #5
Brion55 is offline Brion55  United States
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Here is a way to power your op amps from a single "wall wart" AC supply.
Attached Images
File Type: gif dual supply.gif (4.0 KB, 82 views)
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Old 11th November 2005, 05:06 AM   #6
sangram is online now sangram  India
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I would suggest three audio buddies.

Sorry. Audiobuddy is a small preamp that can do Mic/Line and it's made by m-Audio. I think you can get them for about 70 bucks each off sweetwater or Musician's Friend...
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Old 11th November 2005, 05:30 AM   #7
Enzo is offline Enzo  United States
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What you want is an 8 channel mic mixer. Or a couple of four channel types. You can build circuitry to stick into the existing product, or get something better suited. Consider that if this is to be on the road, it needs to be sturdy and reliable.

If it were me, I might look into a couple old Shure M67 or M68 mixers. One could be slaved to the other for a single output to your sound system. These are on ebay all the time for not a lot. They will run forever. I sold a couple myself not long ago.

There are also the somewhat newer M267/268 units.

The Shure units are easily rack mounted with a bracket or a rack tray. They are basic - no EQ or pan or anything, just level.

Another item is an ALesis Multimix 12R.
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Old 11th November 2005, 12:38 PM   #8
djkib is offline djkib  United States
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Join Date: Dec 2004
Location: Coatesville, PA, USA
That is exactly what I was looking for - I found 5 M68's on line...

I appreciate your input and expertise... I know a reasonable amount about DJ equipment, but am just a neophyte when it comes to actual sound reinforcement and mic mixing... but with help from folks like all who posted, I am learning more than I ever wanted to know!

Thanks for all the great responses!

Keith
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