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Old 22nd May 2008, 10:11 AM   #1
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Question wireless mic transmitter convert for guitar?

I got hold of a wireless mic transmitter and receiver. The transmitter has a small condensor mic hard wired in to the transmitter. I opened up the transmitter, removed the mic and replaced it with a short cord with a 1/4 " phono plug so I could use it as a wireless transmitter for my guitar.I somehow overlooked the fact that it had a condensor mic. I know that the circuitry for a condensor mic differs from a standard wire wound coil style mic. What changes are required to make this work properly. It is a realistic (radioshack) 32-1226 wireless mic, and it is probably manufactured ten or more years ago. Any ideas or comments ?
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Old 25th May 2008, 05:20 PM   #2
Minion is offline Minion  Canada
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There are a few problems with interfaceing a High impedance and fairly high output instrument like a guitar with a Low impedance Highly sencitive curcuit like a microphone input.....

I believe you would have to put a Impedance buffer in front of the Mic input as well as a Pad to lower the output/Input level of the Guitar/Mic....

Also the Mic puts out a Phantom Power so you would need to put a cap on the output of the buffer to block the DC from getting into the output of the buffer......

You could probably not do any of this and just buy a DI box and plug the guitar into the input of the DI box and from the DI output into the Mic input.....

Cheers
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Old 25th May 2008, 06:05 PM   #3
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condenser mics are fairly high impedance devices. you need to pad the output of the guitar and put a cap in series with the output, like so:
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File Type: jpg mic pad.jpg (10.6 KB, 205 views)
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Old 25th May 2008, 07:46 PM   #4
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http://www.tkk.fi/Misc/Electronics/c...s/dyn2emic.gif


Tomi Engdahls page on how to do it
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Old 26th May 2008, 09:02 AM   #5
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dynamic mics have an output of less than a millivolt, condenser mics a few millivolts, and guitars, usually a few hundred millivolys to a volt or two.
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Old 26th May 2008, 12:11 PM   #6
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I took a quick look on the www before posting that link; 'generally' the guitar amps seem to have an input sensitivity of around 30mV.
The dynamic mics I've got put out 5mV or more depending on SPL.
Not an impossible discrepancy them 5mv -> 30mV, nothing a resistor in the right place wont fix.
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Old 26th May 2008, 01:40 PM   #7
Dan2 is offline Dan2  South Africa
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is it not possible to bypass the first gain stage of the transmitter???
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Old 26th May 2008, 11:06 PM   #8
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Thumbs up Thanks for the help

thanks for all of the help. I have a DI box that works.
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Old 26th May 2008, 11:31 PM   #9
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Go on ebay and pick up a used Shure wireless transmitter and receiver. They go for peanuts.

You can construct a adapter to plug into the guitar(1/4" ) and a connector to plug into the wireless transmitter.

Check out ebay 140234664533
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Old 29th May 2008, 02:55 PM   #10
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Default Radio mic conversion for guitar

Hi,

I'm not sure if it will help, but I've just been playing around with a similar idea...

I have a Shure T11 beltpack and the owner's manual tells you how to wire it for all three types of input.

The input is a fairly low impedance ( about 1K ) and is intended to accept a dynamic mic cartridge straight in.

The lavalier mic they supply is an electret but instead of the normal FET buffer stage, there's an impedance converter buffer stage ( using the same type of FET, but wired as a voltage follower ). This drives the 1K load from the source of the FET.

The drain is powered directly from the transmitter, which produces a filtered 5Volt supply for the buffer.

The disadvantage of doing it this way is that it needs a twin-screened lead from the capsule to the plug.

For guitar, they just put 910K in series with the signal and the attenuation is about right.

Being typically awkward, I wanted to use a standard electret headband mic with mine and I've had to build a small adapter box to do roughly the same as they do, just not so neatly... My mic capsule already has the standard FET, so I added another to do the impedance conversion.

I can now use any electret with a 3.5mm jack on it - cheap PC mics, etc... ( the standard connections on a PC soundcard use a 2-circuit jack with the tip and ring connected together )

While I was building the box, I added an XLR and a voltage dropper so I can use the mic direct into my mixing desk and run it from the 48V power.

That way, if the radio reception is bad due to interference at a gig, I can run a standard mic lead with my guitar lead and still get the job done.

Hope this helps, Graham.
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