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Can someone tell me how XLR or A3M 3 pin, low-Z microphone connectors should be wired to the mircophone? I have a low-z microphone cartridge that I want to wire to such a connector. The two wire microphone cartridge has one shield wire and one signal wire. The XLR connector has three pins. How do I wire them together? Help! I need this information before the weekend!
42 responses total.
Yoour michroophone is a 2-conductor , lo-z mic, accoording to yoour description. That's unusual, but not unheard of. Lo-z mics are almost always 3-cnductoor, But, The xlr/a3m wiring key is as follows. Pin 1 is ground! Pin 2 is the poxitive (or hot) lead foor the audio signal. Pin 3 is the cold (or opposite-poliarity) lead foro the audioo signal. Yuu are going to have to make some decisiions PAST just wiringhte mic to the cable. The cord goes into a pre-amp (mixer/whatever) and there are a multitutde of input configurations avaialble. Hi-z 2-wire, Hi-z 3-wire, and Lo-z 3-wire. are the most common. Btw, the 2-wire configurations are also named UN-balanced. 3-wire are TYPICALLY named BALanced, cause there are two audio-signal wires and one groound. The balance is achieved by haveint pins 2 and 3 and equal ammount of voltage above the pin 1 ground connection. Balanced connections don'T pick up nooise adn buzz from "other stuff." UN-balanced connections +do+ pick up noise and buzz from "other stuff." If you are lucky, this 2-wire mic woo'T cause you too many prooblems, but there are TWO wiring configurations to use. (again presuming that the preamp-mixer is a pin-2-hot input). If it's a pin-3-hot input, neither of these wiring schemes will work, which is you only clue to having a renegade mixer. First scheme: mic shield wire soldered to pin 1, only. mic hot lead soldered too pin 2, only. Ignore pin 3 - no attachment. Plug it in and try it out. Second scheme: mic shield wire soldered to pin 1 +and+ pin 3. mic hot lead soldered to pin 2, only. Plug it in try it out. If that doesn't wrk wither, then you have either a bad mic or a renagage mixer. Can't do anything abut the mic - but the connections can be changed: First, use shieldon pin 1 , leave pin 2 unatached and connect the mic hot lead to pin 3, only. plug it in a try it oout. If there are problems, use the second scheme, and tie pins 1 and 2 together (sield/ground) and leave the mic hot lead on pin 3. If that also fails - you are simply SOL. All of the above PRESSUMES that this mic is 2-wire lo-z. good luck
Thanks tsty! Yea, I have since tried to figure out what was going on and a hi-z to balanced line adapter in my Radio Shack catalog gave me a clue. I figured from that that there was probably a transformer involved. One with a center tap so as to achieve the balanced signal you mentioned. I didn't know how to wire it though. I figured that the center tap should go to the center pin, while the remaining two signals, 180 degrees out of phayse with one another, to the remaining two outside pins. I'm not sure about the pin No's. I will have to look into that under the light you have shed. Thanks again.
The pin numbers on a XLR connector are MARKED on the facing of the
connector where the pins are, easiest to read on the female style.
mechanical key \
pin 2 . . pin 1
. pin 3
If you aare thinking abut a RAdio Shack transformer notice that
it is hi-z to lo-z, with the mic connected tothe hi-z end, but yur
mic is a lo-z mic. Wrong connections! Might get some "sound" through
but you'lll be fortunate if it sounds very good (not impossible, just
fortunate).
And if you have to "wire" the Radio Shack adapter, things get into
mathematical combinations WayFast. Bal to un-bal adapters (passive,
like many <not most>) require a transformer. And the wiring can get
very confusing. Here is the basic (only basic)
Bal side un bal side
_____ ______
) || (
) || (
center tap/gnd ----) || (
) || (
______) || (_______ ground
The unlabled connections (not labled ground) are for audio the 2-wire
on the right side and the 3-wire on the left. please note that NOTHING
is herein mentioned about the "z" level of either winding. Either
winding can be hi-z, either winding can be lo-z, the windings can
be the same "z" or different "z's."
*Typically* the 2-wire side is hi-z and the 3-wire is lo-z. But no
guraantees. *If* this is what you get, notice that you'll be connecting
a your lo-z, 2-wire mic to a hi-z, 2-wire transformer winding, with
the lo-z,3-wire winding going tothe cable and then to the mixer/whatever.
That is NOT NECESSARILY better than connnecting without the transformer,
but you'll proabably get _some_ "sound" through anyway.
I got to this item too late but figured it out any way. The information you gave me on wich pin did what was correct. We used it this last weekend and it all worked great! Murphy, where were you? In all honesty I was not wiring a microphone to the motel's PA system, but and inductive "loop". Think of it as wiring a telephone pickup coil to a PA system. (The thing with a suction cup used to record phone conversations) In this case it was a conferance for hearing impared people, many of whome have "tele-coils" built into their hearing aids, used in much the same way as the telephone pickup. I had built a room loop (giant coil of wire hooked to the output of a 100W PA amplifier.) so the speaker could "broadcast" over this audio loop which could then be picked up those with telecoils on their hearing aids. Odd concept, but it works quite well! Since I didn't want the speaker holding 2 mikes (1 for the loop and the other for the motel's PA. Not everone there was hearing impared.) I wanted to couple the one mike into both systems. I didn't have access to the motel's PA, except for the mike input jack, so I decided to use the loop's mike and some how couple it into the motel's PA system. I didn't have much time to do it electronicaly (make a splitter.) so I did the simplest thing I could think of. I wound 100 turns of #28 enamal wire in a 2" coil (z is about 8 ohms) and connected that to a small 8 ohm to 1000 ohm audio transformer from Radio Shack. The 1000 ohm, center taped end was then connected to the XLR connector, just as you mentioned above. By moving this little coil closer to the room loop. I was able increase the coupling, thereby control the volume from the PA. It was cheap, simple and worked great, though next time I'll take the time and build a splitter.
Interesting project. Sounds like there might be a (small) market for portable loop antennas.
Yea, maybe some day. I have also designed and built a X-10 doorbell/phone interface. Too much to do.
Great!
Oh, more April antics. Even the weather decided to chip in.
An electret microphone question: I bought an electret lapel mike from Alltronics. Its specs are: 3-9 VDC, 55-100 uA, output impedance ca 10K ohms. However the plug on its cable is just 1/8" mono (two-wire). How do I wire this (including battery polarity), and does it need an IC amplifier for lower output impedance (and some gain)? I've inspected the electret mike element from RS, and it is 3-wire - two the audio coax, and one for the battery, and the diagram appears to show it includes an amplifier (with an output impedance of 1K).
ummmm, just the element you bought? or the mic as an assembled unit? what is the dbm output level? was there a batterybox included with teh mic assembly? (apparently not, but i thought i'd ask anyway since there is a 1/8 mini-jack apparently hardwired to the assembly.)
Two wire electrets are common. The power goes to the hot (audio) wire through a ~10K resistor. Audio comes form the the same wire and is isolated from the DC power source via a capacitor form .1 to 1 uF. The negative side of the power supply and audio shield are connected to the second wire on the element. It would be a good idea to check with the manufacturer of the mic as to the recommended resistor value. You could also put in a 10K resistor and measure the current (55 - 100 uA) for a given voltage. Have fun! Electrets are neat!
Interesting item! However, one note about balancing transformers: You almost never do with with a center tap. The +/- pair just go into the windings of the transformer. If you grounded the center tap then you can screw up phantom power that might be present on the mixer. (Phantom power is a 48 VDC microphone supply, between ground and the balanced pair.)
The unit is a mike (ca. 0.75"Lx0.5"D) with a lapel clip (and foam cover) and a cable to the plug. No dB info is given. No battery box and no identification. Wait! It came in a conductance-grid bag with the name HONLYCO, and a sticker "Made in Taiwan" on it. KIaus, you are saying the plug tip takes the (+) and the shield the (-), right? I think I'll start at 1M and drop from there (with a 9 V supply). I want to use this for input to a Powerbook. I don't know the input specs on a Powerbook, but it works OK with a dynamic mike.
Yes, Klaus was essentialy correct on how to use that type of mic. The power is usually for a little preamp, since electret mikes have a permanent charge on the element itself, but a little boost is needed. Probably similar specs to a high impedance dyamic mic.
The dynamic mike I have that works OK on the powerbook is a very cheap Sony with 500 ohm impedance. RS's electret mikes indicate 1000 ohm impedances. What is says in the Alltronics catalog is therefore a bit puzzling, unless they really mean the needed resistor. I guess there is nothing for it but to put the iron to the wire.
I wouldn't consider your application to have a critical need for exact impedance matching, Rane. Besides, a low impedance mic can plug into a high impedance input just fine, as long as it can provide enough voltage swing. Most buffered mics like electrets have low impedance and higher voltage outputs. It's only dynamic or transformer balanced mics where you have a big worry about a lower impedance input to allow current flow to contribute, and you've already successfully tried a dynamic mic. (Hint: What is the impedance of a wall output compared to the impedance of a light bulb?)
I understand the point. I am only concerned about trying to drive a low impedance input from a high impedance mike. If the Powerbook input impedance is 500 ohms, and the mike output impedance is 10,000 ohms, then there is a problem.
I'd be real suprised if the PowerBook had a 500 ohm input impedance. Just doesn't make sense, unless it is Apple and they have an expensive mic to sell. Still, active outputs usually do just fine even feeding low impedance transformer inputs.
A "PowerBook" *is* Apple, and they *do* have an expensive microphone to sell (it says in the User's Manual - but I haven't seen them for sale in catalogs, probably because people have discovered that any dynamic (and maybe electret (!) microphone works fine anyway). [I better just rig this thing up now, and report back how it works.]
(Yes, I knew that the PowerBook is an Apple product... That was a joke about Apple and standards. :)
Most sound cards, cassette players, etc. have 600 ohm input impedances. 600 ohm mics are common, common, common! Your electret should work just fine Rane. I'll bet the tip on your mic plug is for power in (Through a ??K resistor) and audio out (Through a .1 to 1 uF capacitor). The sleve on the plug is than common for power and audio. Give it a go and see what happens. BTW, 500 ohm impedance is plenty close enough to 600 ohm...
With an input impedance of 600 ohms, I would need a 5 ufd coupling capacitor for a half-power point at 50 Hz. Lo-and-behold, the RS electret element has with it a circuit showing "3-10 ufd" cap being used, and I just happen to have a 10 ufd rated at 35V....things are coming together (now, where is that spare project box...). All this trouble, by the way, is to tune my harpsichord with this Powerbook and LabMeter v2.0 - my tin ear has always had trouble with equal temperment.
10uF than ;) The positive side goes to the electret end and the negative side to the audio input. Many years ago, an engineer told me that Tantalum capacitors were better than Electrolytic for audio coupling applications. I don't remember why. (Perhaps it had to do with the memory effect displayed by the dielectric they use.)
Tantalums are "electrolytic" too. Now, here's another puzzle - my 10 ufd cap is not marked (+) and (-), but rather has an arrow symbol pointing to the "can" end (though the arrow has a sort-of dash in it....). Anway, I presume the "can" is (-) - at least it was when I was a kid!
Yep, that "sort of" dash in the arrow is a minus sign. The arrow on an electrolytic always points to the negative terminal, almost always the can.
The arrow symbol is also used on a diode, which I have taken to mean the direction of easier conduction of *positive* current. However a capacitor stops current, so the same idea doesn't apply (except to the more obscure "displacement current"). Do you know where the respective conventions arose?
Arrows are used on diodes to denote the "cats wisker" or anode end. In this case positrons do indeed flow in the direction the wisker or arrow is pointing. The big arrow going down the side of aluminum electrolytics is used by automated pick-n-place equipment. An optical scanning device looks for the direction the arrow is pointing to determin the correct orientation of the device. It also aids unskilled labor in loading insertion equip- ment. Lead length is also often use on polarized devices. The shorter lead is generally negative. Be forewarned: The dash mark on Tantalums is on the positive side of the capacitor! (Sort lead is generally negative here too.)
You use positrons in your circuits, Klaus? WOWZER!
ummm, as teh audio industry moved away from "power transfer" and into "voltage transfer" as the preferred method for moving a signal from a source to a load, the actual imput impedance (what the source "sees" as a "load) went wayyyyyy up. part of that move was based on having non-transformer loads attatched to non-transformer sources. examples are rampant. however, the markings are still confusing. a load can often be labled as "wanting" a source impedence feeding it of 600 ohms (fer example) while the *actual* load impedence is 10K-50K or more. this permits voltage transfer not power transfer. conversely, a source can be labled as wanting a 10K ohm load while the actual source impedence is 50-250 ohms. So .... this 10K mic and this 10K load APPEAR to be "matched." are they, in fact, "matched?" Hardly! however, teh saving grace in all of this is that the "10K mic" would burn out if asked to drive a "matched (600 ohm) load because of all the current that the load would demand. and/or the batteries wouldn't last more than a few hours. part of this charade also creates another apparent problem when the actual impedances are used. it's not warm-n-fuzzy to hook up something labled 150 ohms to something labled 15,000 ohms. so what do you do if you don't "like" the numbers? either recognize that this hookup is actually correct, or massage the numbers to create the appearance that all is well, numerically, and let the physics fly cause it's gonna be fine anyway, numbers notwithstanding. so, having a lo-Z mic driving a hi-Z load (real impedences) is not a problem. it's the voltage swing that is important. real power consumption is delayed until it's time to move some mass, like a speaker cone. (good point above, the wall socket/light bulb situation) another point well made, above, is to de-couple the DC of the mic circuit from the input of the computer. actually, it's better than a good idea, it'll keep you from frying the audio input of the computer. if you use a capacitor, the larger the capacitance, the better the low frequency response will be ..."better" being more low frequencies are passed into the computer, *if* that's what you want. if you dont' like the low end, increase the capacitance. if there is too much boom adn room rumble, lower the capacitance as you see/hear fit. as far as the computer having a phantom power source ....ummmm, nah don't think so, that takes three wires and there is the risk of shorting out that power supply, and on and on ... only mics that require *power* instead of voltage would need that and those are kinda rare these days in the consumer end of things.
Thanks TS. I'm aware of the technical aspects, but have been less than clear on the practice. I tend to think in terms of "voltage transfer" myself, but there are issues of frequency response, noise, long lines, distortion, etc, which are involved in "load matching".
Er, TS, don't you mean "decrease the capacitance" to reduce low end? Actually, high impedance has been with us since the dawn of active electronics, since tubes like a high impedance input signal (big voltage swing, not much current needed to drive a grid). Low impedance came about as a cable noise reduction technique, pioneered by the phone company (with *miles* of line, little things like impedance and balancing signals pay off big). Transistors are actually pretty happy with low impedance operation, but all the equipment (cheap mics, guitars, etc) are high impedance already. Low impedance quite often requires a transformer at the input end, and a good input transformer can set you back $50 if you are fussy or professional.
I occurred to me after I wrote #30 that I was influenced by my father, who was a telephone engineer, and also worked on shipboard PA systems during WWII. He brought home surplus 600 ohm line transformers for me to play with.
I wired up the circuit for the electret mike, using a 100K resistor to limit the current to 90 uA (from a 9 volt battery), per the mike specs (50-100 uA), and the 10 ufd electrolytic capacitor. I connected it to the Powerbook mike jack and....NADA! A dynamic mike still worked OK with the Powerbook. I measured the current from the electret mike jack, while connected to the Powerbook, to check that the mike was being powered, and found 115 uA. Now, that was weird, because I had checked just the circuit earlier and found an acceptable 93 uA. I then unplugged the circuit from the Powerbook, and the mike current dropped to 93 uA. I measured the voltage on the Powerbook mike jack - it is 8 volts (tip +). I also shorted it and measured 10 mA current, so the DC source resistance is 800 ohms. Therefore, the Powerbook was reverse-polarizing the coupling capacitor with 8 volts. Does an electrolytic act as a capacitor if reverse polarized? I also measured the electret mike resistance, and found 2,500 ohms. It was therefore not affecting the currents that were measured. (For the record, the dynamic mike DC resistance is 405 ohms.) To check out the electret circuit "as designed", I plugged it into my audio system. It gave a stronger signal than the dynamic mike, so the mike circuit was OK, but not with the Powerbook mike input. The problem does therefore appear to be the reverse polarization of the capacitor. It seems that I can forget about the battery supply for the electret and use the Powerbook 8 volts. Just a series resistor of ca. 80K bypassed with the 10 ufd cap (turned around for proper polarity) should work. This suggests that the "official" Apple microphone is just such a device.
Why not just plug the electret directly into the input? Doesn't sound like you have an excessive current problem, and you don't really need to get rid of a bias that already exists from the input itself.
Forget (most of) 33 - I made an error. To explore the prospect of connecting directly, I lowered the current limiting resistor. As I did so, I measured voltages and calculated the apparent resistance of the electret. As the limiting resistor goes down, the current goes up a *little*, but the voltage increases greatly. At 21,000 ohms, the voltage across the electret is 4.5 volts, and the apparent resistance is 19,000 ohms (with a current of 240 uA). So! - the electret is very nonlinear. I therefore dared to plug it directly into the PB - NADA. That was strange, if the PB was supplying 8 volts. I even tried the electret again on an audio amplifier with the smaller limiting resistor, and it is *very* sensitive. What was wrong? After fiddling quite a bit, I discovered that my cable to the Powerbook wasn't fully in because the plug's shell was too big. Fixing that, and getting it all the way in - there is no 8 volts on the PB mike connection! The jack must have a contact that opens on inserting the plug, removing the 8 volts from the tip. So, now I put it all together - and it works great on the PB! I then analyzed the circuit, and found that there is a compromise between sensitivity, which is greatest with the highest voltage on the electret, and the frequency response, which goes to pot (low frequencies are lost) as the current limiting resistor is decreased. I settled on 15K. Klaus was right all along. Thank you all for making suggestions. They led me to explore other things and also helped me overcome some trepidations about zapping the unit. By the way, I am now "off appointment" for the summer, which is why I can spend some time on these projects that have been sitting around for quite a while. There are more ... I'll be back in another item for more advice!
I once disected a dead electret element. It looked very simple. Just a very thin metalized plastic diaphragm streached over an aluminum ring. Just under the diaphragm was the center leg of what looked like a FET transistor. This leg did not touch the diphragm but was very close to it. Being a form of amplified condenser mic, I suspect that it was the changing capacitance between this leg and the diphragm that produces the initial electrical signal. The FET then transmorms the impedance to something a LOT lower, thereby amplifying the signal. There were no other electronic components inside! The relationship between suppy current and frequency responce you found is quite interesting. I will have to remember that the next time I use one!
I "modeled" it as a variable condenser with a resistor and battery across it. The battery voltage I took to be that I found across the electret as I varied the resistance (current) on the real unit. As the capacitance is wiggled, a signal voltage is developed across the resistor. The magnitude of that is proportional to the voltage across the electet, which goes up as the resistance is lowered, but the low-frequency cut-off increases in frequency as the RC product becomes smaller (clearly at R ->oo, I have no voltage, and hence no signal, and as R->0, the voltage goes to a maximum but the response goes to zero). This model helped me understand better why I don't want to keep lowering the resistance, but I cannot assign a particular value of the capacitance for the device. There is an apparent capacitance, though, as the voltage across the electret did not change instaneously when I changed the resistrance instantaneously. The FET must, in effect, be amplifying the capacitance, rather than just a signal. It is certainly hard to find out how things like this work. The ARRL handbook just mentions electrets, but gives no details. I found the same problem in trying to look up how an electrolytic capacitor behaves when the applied polarity is reversed (what capacitance does it exhibit?), or even what "working voltage" really means (one source just said it is a limit, while another said not to use an electrolytic at "much" (unspecified) less than its rated working voltage.) Where are such specifics explained?
I would suggest contacting the people who made the device in question.
ummm, increase the capacitance (series fed) to increase the bass response and lower the capacitance (series fed) to lower the bass response, in response to scott's #31. big Uf, lotsa bass; small Uf, small bass. i did say it right, but with, i guess, unusual wording - sorry. glad it works rcurl.
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