Mic Conversion

[unclej]

sunday afternoon one of my regular customers dropped off an old mic that had a four prong receptacle for the cord. he left the cord that came with it years ago and a standard cord with three prongs connectors and wanted to have the mic converted so that he could use it in his PA. i had a store full of people and didn't really have time to talk with him and after he left i started wondering if it can be done.

can anyone tell me what the fourth wire on an old mic was for..will it work with just three wires and if so how do i determine which one can be eliminated. i'm assuming that if it can be done that i can just splice the three prong female connector onto the end of his four wire cord leaving the four prong male connector on the other end to fit into the mic.

thanks

[Paul Marossy]

Hmm... that's a good question. I hope someone here knows the answer because that has also sparked my curiousity!

[ansil]

hmm do you have a pic. does the four connector lead into a standard three connector?? if not what was he using it on, a cb radio? those had four conductors. i have never seen one that didint' have a three prong end ie the adaptor cord .

if thats the case you just find which prong goes to which end of the adaptor.

[unclej]

i really don't have any more info at this time. i've been off since it came in. he brought the mic in with one cord that had a four hole female connector on one end and the connector cut off on the other. he also provided a standard three prong cord. in the morning i'm going to cut off the male end of the three prong cord, bare the wires, plug it into my PA, bare the wires on the four wire cord and with three jumpers see if there's a combination that will work.

i don't know what the mic went to originally but i know it's probably out of the 50's. i'll post my results sometime tomorrow.

[MidnightLamp]

A lot of special microphones like that that I've seen with four prongs had the fourth prong as a power rail, and sometimes a fifth prong as an isolated power ground.

[unklmickey]

hi UncleJ,

you didn't mention the make or model of that mic.

many of the older mics used a 4 pin connector with a threaded retainer ring.

some of them connected a low impedance winding from an internal transformer to pins 1 & 2, and a high impedance winding to pins 3 & 4.

but, without knowing the make and model, you can't be certain how it's wired.

cheers,

unk

[unclej]

thanks unk..i'll post a pic and the name in the morning when i go in. at this point i don't know if i can help him or not but i'd like to if i can. he's been a good guitar setup/repair customer.

just for the heck of it i just googled "microphone forums" and sure enough there seem to be a lot of them so once i post the specifics of this mic i may be able to find what i need there if no one here knows the answer.

MidnightLamp..thanks for your input as well.

hi UncleJ,

you didn't mention the make or model of that mic.

many of the older mics used a 4 pin connector with a threaded retainer ring.

some of them connected a low impedance winding from an internal transformer to pins 1 & 2, and a high impedance winding to pins 3 & 4.

but, without knowing the make and model, you can't be certain how it's wired.

cheers,

unk

[unclej]

allright...i forgot my camera but it doesn't matter. these guys were very accomodating. the mic is an old electro-voice model 664 and unk seems to have nailed it. stamped on one side is the following: "impedence changes are made on the cord plug. plug shell and no. 1 contact are ground. contact no. 2 hi-z. contacts no. 3 and 4 160 ohm.

now, armed with that info can anyone tell me which of the 4 wires on the original cord can be attached to which three wires on a three prong cord to make it work in a modern PA? the female plug end that attaches to the mic is labeled 1 thru 4 so it will be easy to trace the wires.

i guess part of what i need to know is what the three wires on a modern mic cord are for and if it will work as a low-z mic. if so it would seem logical that i could atach ground to ground and then the two remaining wires to #'s 3 and 4.

thanks

[Steve Exton]

allright...i forgot my camera but it doesn't matter. these guys were very accomodating. the mic is an old electro-voice model 664 and unk seems to have nailed it. stamped on one side is the following: "impedence changes are made on the cord plug. plug shell and no. 1 contact are ground. contact no. 2 hi-z. contacts no. 3 and 4 160 ohm.

now, armed with that info can anyone tell me which of the 4 wires on the original cord can be attached to which three wires on a three prong cord to make it work in a modern PA? the female plug end that attaches to the mic is labeled 1 thru 4 so it will be easy to trace the wires.

i guess part of what i need to know is what the three wires on a modern mic cord are for and if it will work as a low-z mic. if so it would seem logical that i could atach ground to ground and then the two remaining wires to #'s 3 and 4.

thanks

Standard 3 pin cannon plug mic wiring is Pin 1 Gnd, Pins 2 & 3 balanced mic. I would try the following:-

4 Pin Plug from Mic 3 Pin Plug to Amp

1 --> 1

2 not connected

3 --> 2

4 --> 3

This would give you the low impedance balanced output from the mic into pins 2/3 into the amp, and the ground connected through.

[unclej]

thanks steve..i'll try that this morning when i go in and post results.

[unclej]

well..that didn't turn out to be nearly as challenging as i thought it would be. when i disassembled the four prong male connector that attaches to the mic i discovered that it was only a three wire cable so it was hooked up as a regular mic. all i had to do was attach it to a regular cable.. ending up with two three prong male ends and the mic worked fine.

thought i had a real brain teaser.

thanks again for all the input and next time i'll try for something a little more challenging.