Audacity Forum

I realize this has been discussed on this REALLY old thread ( http://forum.audacityteam.org/viewtopic.php?f=27&t=5569 ) but if anyone's still out there lol...

I have a Yamaha mixer with preamps on 4 mic channels and I have the same problem with wanting to use three Plantronics Gamecom 367 Headset Mics with it.

I stared at the photos of the custom adapter boxes and diagrams on that thread for about a full day and decided there's no way I can even attempt building one without detailed instructions and pictures, etc.

I DID however find this guy's video that solves the same problem a different way. Is there any reason his method wouldn't work for me? He says something about not needing capacitors because the device has it's own and can separate the DC etc, etc.

"Making an adapter lead for a headset microphone so I can use it with an ordinary mic input"
http://www.youtube.com/watch?v=lh0RgXO4WWE

THANKS!!!

Reply copied from other thread:

steve wrote:

acousticdj wrote:"Making an adapter lead for a headset microphone so I can use it with an ordinary mic input"
http://www.youtube.com/watch?v=lh0RgXO4WWE

My complaint about so many YouTube videos is that they frequently miss out important detail.
At about 5 minutes into the video he jumps from soldering the input socket to suddenly having the whole thing complete. Where did he connect the battery?

Fortunately there is a circuit diagram here:
http://www.epanorama.net/circuits/micro ... ering.html


He has missed out the capacitor on the assumption that the microphone input has a DC blocking capacitor capable of handling up to 9v on the input. That's probably a fairly safe bet for his old Akai reel to reel but I'd not like to rely on it for consumer grade modern equipment. Depending on the input design of the microphone pre-amp, 9v DC across the input could fry the pre-amp (irreparable damage). Even if it does not destroy the microphone pre-amp it could cause the microphone signal to be useless through either a huge amount of DC offset or high noise level. The purpose of the capacitor is to prevent DC going into the microphone pre-amp. The capacitor should be present.

Thanks man. I still wasn't solid on what the symbols on the diagram meant (total electronics newb sorry) so I did some more homework and came across this video.

http://m.youtube.com/watch?v=JPxqluZkS2o

It's in Spanish (I think) but it shows really clearly how to build this circuit without soldering! It even shows how to build one out of household items lol. The guy was making it so he could plug a PC mic into a guitar effects pedal but I think it's exactly what I need, right?

I figure I'll put everything in a metal box and tie all the grounds to one point on the box to finish it off. I'll also probably wire some kind of 1/8 female connector to the circuit instead of the headset mic directly so I can plug the headset mic into it instead of permanently connecting the headset to the box. I think I'm finally on the right track!

Perhaps this will also help (click on the picture to expand it to full size):
Good luck
If you get it working it'd be good if you could post some detailed photographs/

The guy was making it so he could plug a PC mic into a guitar effects pedal

That's what his intention was, but I bet it didn't work. The guitar pedal takes high level signal from a guitar or other instrument, but the output from a headset microphone is still a microphone -- really tiny, delicate signal.

The adapter is only the front half of the solution, you also need to plug the system into your mixer.

http://www.kozco.com/tech/audacity/pix/ ... attery.jpg

I may have better pictures around. This was not built as a graphic illustration. Koz

Thanks so much guys. Your assistance is truly invaluable.

So unfortunately a trip to Radio Shack left me underwhelmed and empty handed. Fortunately though there's a huge electronics supply house in my area that should have everything I need and then some so I'll check them out tomorrow and definitely post some pics of my progress!

In the meantime, a couple of questions about the diagram. (The Radio Shack guy gave me a deer-in-headlights look when I asked him lol. I'm hoping the guy tomorrow knows his stuff though.)

1) What size resistor and capacitor should I use??

a)The guy in the first video I posted said to use a 2.2k resistor (and didn't use a capacitor, which I will need to use as discussed previously).

b)The guy in the second (Spanish) video says to use a "1800 ohms 1/2 Watt" resistor and shows a yellow "220k/250V" capacitor in his circuit. Radio Shack didn't carry either of those.

c)The color diagram you provided says to use a resistor "Equal to required impedance EX.= 1000 ohm" and a Capacitor "Most any value 10uf 16v". I'm not sure what either of those mean (sorry) and I don't know the impedance of my microphone. The manufacturer doesn't provide the information anyhere. Is there a typical or average best guess impedance for these kinds of microphones? This is them: http://www.bhphotovideo.com/bnh/control ... &A=details

d)In the photos of the boxes/circuits that Koz has made, there are TWO resistors used in each circuit instead of one, so that's really confusing me too. I don't think it was ever mentioned which kinds of resistors or capacitors are used in these boxes specifically.

Thanks again guys. I feel like I'm almost there.

Have a look at this page - lots of information. http://www.epanorama.net/circuits/micro ... ering.html

The component values are not critical.

Resistor: about 1 k Ohm (also described as "1k0" or "1k")
Possibly described as a "metal film resistor" (the material that it's made from) with "axial leads" (leads sticking out of the ends).
Anything from about 820R up to about 2k2 (2.2 kOhm) will do.
1/4w or 1/8w or 1/16w (250 mw or 125 mw or 62.5 mw)

Capacitor:
About 10 uF (10 microfarad) 16v "Electrolytic" or "aluminium" capacitors.
This is a very common value, but other common values that will do are:
22 uF or 47 uF as either 16v or 25v.

These components should not cost more than a few cents/pennies each.

I'm looking for the original of that picture. It's not reduced in size for publication. The extra resistor is to make the capacitor happy and to prevent serious pops when you plug the unit into your mixer.

You should always use 2200 ohms (or 2.2K -- same thing, red, red, red). That's the value of the resistor inside most sound cards, and it's the value most microphones are designed to work against.

Capacitor values (taken in reverse order): the voltage rating should be higher than the voltage expected in the circuit. In a sound card, that voltage is five volts, but in your circuit, it has to be higher than the battery you use. My illustration is six volts and yours may be nine volts, so a 15 volt capacitor is just about right. A much larger rating may actually be counterproductive because the insides of the capacitor will start loafing and not do its job.

The capacity value affects the fidelity of the microphone and is a lot more complicated -- and yes, it does matter. The smaller the value, the less bass volume you will get. I picked 100 ufd as being a good tradeoff between physical size and good fidelity. Some would say good bass volume is a liability in a voice circuit and many of us go to steps to reduce the bass volume. But there it is.

This would work nicely, but the closer you can get to 100 ufd at 15 volts the better. Please be aware that these devices have polarity. You have to install them in the right direction.

http://www.radioshack.com/product/index ... d=12448318

The (-) is marked on this part. I usually mark the (+) on my schematics. They're the reverse of each other.

Putting nine volts into an audio circuit expecting no volts, or at worst five, can reduce your sound card to garbage, so the capacitor is a good thing.

The extra resistor is a 10K (10,000 ohm) resistor (brown, black, orange) and its job is to gracefully bleed off the explosive pop you can get if you plug this this into a working mixer.

I have a hand-drawn circuit around here somewhere.....

Koz

The "hot" wire from the circuit goes to pin 2 on the male XLR connector that you plug into the mixer. The cold wire or ground goes to both pin 3 and pin 1. This is an "unbalanced" electrical circuit unlike a regular microphone and the cable shouldn't be much over three or four feet long.

The 10K resistor goes between the two , but physically back in the circuit.

I see the 10K is included in one of the schematics Steve posted. See, I'm not crazy.

We are talking about managing microphone signals here. They're really tiny and that's the reason I picked a metal box and I'm using shielded cable between the circuit and the mixer. If you don't do that, the circuit will pick up buzz from every CFL light you have in the house.

Koz

acousticdj wrote:I have a Yamaha mixer with preamps on 4 mic channels

What sort of microphone connections? 1/4" jack or 3 pin XLR?