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Help understanding the proper way to connect a cheap mini/lapel condenser microphone
Help understanding the proper way to connect a cheap mini/lapel condenser microphone
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Old 8th November 2017, 07:48 PM   #1
16gnomes is offline 16gnomes  United States
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Join Date: Mar 2014
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Default Help understanding the proper way to connect a cheap mini/lapel condenser microphone

I apologize in advance for my lack of understanding on this subject. I have purchased a few small, cheap, condenser microphones and have tried for the last few days to understand how to properly connect them but have found myself over my head once again. I know most everyone on these forums are experts on the subject and hope to receive the proper guidance.

These are the units I've purchased: DGFAN Lapel Micphone(GL-300)

What I've found so far:

1) Using an adapter and connecting to a standard Mic input does not work at all. Probably not a surprise to you, but it was a surprise to me.

2) I've measured the impedance of the 3 pins and found 1.3kΩ between pins 1 and 2, 1.3kΩ between pins 1 and 3, and .7Ω between pins 2 and 3. This is counting from the inner conductor of the 3.5mm plug being pin 1 and the tip being pin 3.

3) As this unit is meant for PC use, and I believe it is a capacitor microphone, I've found the following article that illustrates a +5v bias is expected against pin 2: Sound card microphone

4) I know phantom power is different and that employing phantom power may damage these microphones as illustrated in the "Other Microphone Powering Techniques" section of this article, so I have not tried it: Phantom power - Wikipedia

5) I've attempted to find some type of adapter that will provide the +5v and effectively convert the mic to connect to a pro audio input, but have not found anything yet.

I'm fully expecting the standard answer to be, "Stop messing with this cheap crap and get yourself professional lapel mics!" Of course I know this, but frankly I cannot afford any more gear at the moment. Plus, this project will allow me to learn more about this technology which I am eager to do.

Thank you.
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Old 8th November 2017, 08:46 PM   #2
16gnomes is offline 16gnomes  United States
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I think I just found the proper adapter type, would really like to know how these are made if someone would be so kind to help me with that: Introducing the VXLR+ - YouTube
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Old 8th November 2017, 10:31 PM   #3
MAAC0 is offline MAAC0  Portugal
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First You must determine the pinout. Connect it to a laptop and try to record some voice. If it works You have the correct Ground (Sleeve)-Bias (Ring) -Output (TIP) pinout.
You could use a 5V USB or some sort of DC wall wart charger for powering the mic. On computers I believe ring is for the bias Voltage. If You connect the sleeve and ring to the USB adapter. The audio output should be between sleeve and tip. I would put a 25 to 47uF /63V capacitor in series with the tip for safety reasons if You accidentally switch the desk phantom power on. Capacitor Plus faced to desk input. Try the best value for the bass needed.


Or


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Old 9th November 2017, 12:42 AM   #4
16gnomes is offline 16gnomes  United States
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Thank you MAAC0, yes the mics work fine when connected to a PC.

I'm hoping to connect them to a Roland R44 for mobile recording use, so trying to avoid wall warts or a PC. I was thinking of making a box with 3 AAA batteries in series to drive the bias through a 2.2kΩ resistor as illustrated in the "Sound card microphone" link in the original post, which is I expect how a PC would be running the circuit.

What I'm hoping to get help with here is how to properly connect this to a standard XLR mic preamp input, such as those on the R44. I expect there may need to be some modifications to the circuit when connecting to pro audio.

I went ahead and ordered the Rode VXLR+ adapter but I'm not quite sure if it'll work. Ordered from Sweewater since they'll let me return it if it doesn't.
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Old 9th November 2017, 07:35 PM   #5
16gnomes is offline 16gnomes  United States
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If anyone is interested, I believe further research has provided me with the answer but of course always interested to hear from someone who actually has experience wiring up something like this.

These microphones are unbalanced electrets, which have only 2 conductors but the 2nd and 3rd pins separate the signal from the +5v bias with a capacitor: Electret microphone - Wikipedia

Since no professional PA gear is setup to provide a bias for an unbalanced input, even if the electret was designed for +48v across pin 2, phantom power is also providing +48v across pin 3 effectively nulling the potential across the output capacitor of the electret.

What I believe the Rode VXLR+ must be doing is taking the +48v phantom across pins 2 and 3, somehow reducing the voltage to +5v and applying it only to pin 2 of the electret, then converting the unbalanced output to balanced on the XLR. Looking into the circuitry required to do both of these things, properly, I'm starting to think $25 a pop for these adapters is a pretty darned good deal

Definitely looking forward to hearing the results.
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Old 11th November 2017, 12:16 AM   #6
Zero D is offline Zero D  United Kingdom
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@ 16gnomes

As you've discovered, pins 2 & 3 are connected together = quite normal for these types.

I expect you know the R-44 includes mics ? so you want to use an external one. But it also has Phantom Power to feed external mics

Quote:
Although the R-44 is compact, all the necessary functions are included. Built-in high quality microphones and speakers make recording and monitoring without external devices possible.

Analog Input Ch 1 - 4 : XLR/TRS Combo type, XLR type (phantom powered)

Phantom Power 48 V + or - 4 V, 8 mA per 1 channel

Roland Pro A/V - R-44 | 4-Channel Portable Recorder
So you won't need a seperate supply/batteries

Quote:
What I'm hoping to get help with here is how to properly connect this to a standard XLR mic preamp input, such as those on the R44. I expect there may need to be some modifications to the circuit when connecting to pro audio
Here's a couple of www's that should help. Concentrate on just the ones i've highlighted though, otherwise you might get bamboozled with too much info
Quote:

Figure XXXVIII. Phantom Powering the WM61A Electret Microphone
John Conover: Using the Panasonic WM61A as a Measurement Microphone
And a balanced

Quote:
Source: PZM Modifications web page by Christopher Hicks.

Here is a easier to read circuit diagram for the circuit shown above
: Powering microphones
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Old 12th November 2017, 04:51 AM   #7
16gnomes is offline 16gnomes  United States
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Thank you!

Yes I know it has built in mics, and phantom power, but I want to connect 4 independent ones on lapels for an interview type scenario and record to independent channels so I can mix them into a good quality video without having everyone hand a mic around or try and use one central mic. It's more of a, hey, will this work? Kind of thing and to practice my skills.

Just hungry for info these days so really appreciate the feedback!
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Old 12th November 2017, 05:35 AM   #8
basreflex is offline basreflex  Spain
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just use 2 aaa batteries as a 3V source per mike and the schematics from the "powering microphones" pages.. constructing a 48v phantom power circuit for this mike is a lot more work ..
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Old 12th November 2017, 08:51 AM   #9
Zero D is offline Zero D  United Kingdom
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@ 16gnomes

Yeah the Rode VXLR+ adapter should do exactly what you want. Missed that I didn't realise they existed, until now

All the best with your recordings
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Old 13th November 2017, 05:36 PM   #10
16gnomes is offline 16gnomes  United States
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Quote:
Originally Posted by basreflex View Post
just use 2 aaa batteries as a 3V source per mike and the schematics from the "powering microphones" pages.. constructing a 48v phantom power circuit for this mike is a lot more work ..
Thank you, I had mentioned in a previous post I was considering employing 3 AAA batteries, but it was the means of connecting properly to the XLR that I was still fuzzy about. I wasn't trying to build a balanced 48v source at any point.

The reason I'm buying these adapters is because they both convert the 48v to 5v and convert the electret's unbalanced signal to balanced, doing both is a far more complicated circuit than I ever expected although I still may try it someday if these end up with decent sound quality.
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