Vintage 4-pin Mic Wiring Help

[jjasilli]

Seeking help on how to wire a vintage 4-pin mic. 

I have two Univox MDF614, Cardioid-Dynamic - Dual Impedance Microphones.  Supposedly Univox's quality mic of the early '70's.  HI Impedance is 50K; LO Impedance is 600R.  Two wires emanate from the element into the body of the mic.  There is on ON/OFF SW but no impedance selector.  Output at the tail-end is a male 4-pin jack.  It takes an old-fashioned, Amphenol-style 4-pin, screw-on, female plug.

Through trial & error I've wired the plug to sort-of function, but the sound is trebly & thin, with early feedback when plugged into a guitar amp. Research indicates that 4-prong mic connections were common back then, but with no standard wiring schemes. 

Does anyone know how to wire these things, or how to sort it out?  How do I tell if I'm getting the Hi or Lo impedance?  Which one do I want?  Can I terminate the other end of the mic cable in an XLR plug?

Thanks!

[terminalgs]

Seeking help on how to wire a vintage 4-pin mic. 

I have two Univox MDF614, Cardioid-Dynamic - Dual Impedance Microphones.  Supposedly Univox's quality mic of the early '70's.  HI Impedance is 50K; LO Impedance is 600R.  Two wires emanate from the element into the body of the mic.  There is on ON/OFF SW but no impedance selector.  Output at the tail-end is a male 4-pin jack.  It takes an old-fashioned, Amphenol-style 4-pin, screw-on, female plug.

Through trial & error I've wired the plug to sort-of function, but the sound is trebly & thin, with early feedback when plugged into a guitar amp. Research indicates that 4-prong mic connections were common back then, but with no standard wiring schemes. 

Does anyone know how to wire these things, or how to sort it out?  How do I tell if I'm getting the Hi or Lo impedance?  Which one do I want?  Can I terminate the other end of the mic cable in an XLR plug?

Thanks!

I'm guessing the actual coil attaches to the diaphragm is 600ohm,  and there is a 600ohm:50K transformer.   But, maybe we don't have to guess.  See if you can open the mic up.   mic's often can be disassembled (one end is threaded into another).   Open it up and see what pins are connect to which, and see what the the switch does.   

[jjasilli]

OK, thanks - made some headway. The only SW is merely ON/OFF. I measured the static DC resistance from lug to lug, as follows:  1-2: OL; 1-3: 1.482K; 1-4: 1.420K; 2-3: OL; 2-4: OL; 3-4:  64.5R

Maybe it works something like my Shure 556sd which is also dual impedance, schematic attached.  To change the Shure's impedance, you loosen a set screw, pull-out the mic's XLR jack, then reverse an internal jumper to connect the desired impedance wire to the inside of pin3 (pin4 is inoperative and is just a place holder for the unwanted impedance wire).

For the Univox mic, it seems that the 2 outputs might be internally pre-wired to the pins.  The female mic jack would then be wired for the impedance you want; then terminate the other end with a phono plug for Hi-Z, or an XLR for Lo-Z.  

It's getting more clear, but I'm not quite there yet.  The highest impedance must read between the common pin > both secondary windings in series.  Not yet sure which Pin is ground.  



 

[terminalgs]

the resolution on your image is low (or at least, I can't zoom in with any clarity) have you got a better pic with the wording  on those windings?

[PRR]

> 1-2: OL
> 1-3: 1.482K
> 1-4: 1.420K
> 2-3: OL
> 2-4: OL
> 3-4: 64.5R

3-4: LO
1-4: HI

(ie, to change Hi/Lo, move wire from 1 to 3)

> Not yet sure which Pin is ground

Measure Case to pin 2.... is that zero or open?

Plugged to guitar-amp: call pin 2 (I think) Shield, pin 1 Signal-, call pin 4 Signal+. At the 1/4" plug end (or at 4-pin end if you must use single-circuit cable), connect Shield and Signal- together.


> I'm guessing the actual coil ... 600ohm

The voice coil is surely closer to 10 ohms. Anything higher requires super-thin wire which breaks or corrodes-through too easily. If the mike is _only_ offered 150 ohms. it may be worth the trouble to wind for 100+ ohms. But since this has a HI-Z output, it has an internal transformer. Then it is just as easy to transform 10 to 150 on the same transformer.

Shure SM57/58 also has 10 ohm VC and transformer, because it comes from a line of hi/low Z mikes with internal transformers.

[DummyLoad]

if the schematic posted is one of the subject microphone...

if i'm interpreting the schematic correctly then:

1 - is case > ground

2 - is LoZ sig. (+)

3 - is LoZ sig. (-)

standard XLR LoZ mic. wiring.

for HiZ use 2 & 4; strap 2 to 1 and that's ground - 4 is hot.

[jjasilli]

the resolution on your image is low (or at least, I can't zoom in with any clarity) have you got a better pic with the wording  on those windings?

Here's links with more data on the Shure 565sd:  http://www.shure.com/idc/groups/tech_pubs/@global_managed/documents/webcontent/us_pro_565d_ug.pdf

http://www.shure.com/idc/groups/tech_pubs/@global_managed/documents/webcontent/us_pro_565sd_ug.pdf

Will continue to test the Univox mic's when I get a break later today.