does anyone understand microphone wiring

[keat63]

I have a cheap Karaoke mic, which has a bizzare issue.
When i switch it off, the diaphram is still active, but not fully active.
Over a period of a few seconds, the input fades away, however, if i shout loudly in to it and turn up the volume on the amp, i can still hear input from the mic.

I opened it up, and I can't figure out how the switch works.
It appears to be a 3 pole on off switch.

From the XLR plug, i've 3 wires, Black, Red and Yellow.
The black wire (which I assume is ground) is soldered to the metal case of the switch.

Then both the red and yellow wires are soldered to two of the switch pins, which in turn run to the diaphram.
Its as if the switch is being bypassed, unless the ground is somehow involved.

Aplogies for the rubbish drawing

 

[duke37]

My guess is that the microphone is slowly discharging when the switch is turned off

 

[keat63]

It's the switch i'm struggling with.
In my rough diagram, the switch is in the off position, however, considering the cables are effectively wired straight through, the switch appears to have no effect in the off position.
And with the switch in the on position, the red and yellow would be connected.

It doesn't make sense to the way I understand switches to work.

 

[Harald Kapp]

As shown in your sketch it doesn't make sense to me either. Can you upload a crisp foto of this microphone/switch arrangement?

 

[keat63]

I'll open it up again this evening.
I do have another identical mic, which works OK, and I could use for comparison, but I don't particularly want to open it up if I could avoid it

 

[Harald Kapp]

Understandable.

 

[duke37]

I have not seen a switch with the side comtact. My guess is that the top wire is a power wire to energise one side of the microphone. Look up Wikipedia to try and find the type of microphone.

 

[keat63]

I opened up both mics, they are both wired the same, so I can rule out any dodgy wiring/soldering.
I took the yellow pair from one leg of the switch, soldered to the other unused leg and rotated the switch through 180 degrees.

It's still the same, so I guess I can about rule out a faulty switch.
or maybe maybe the centre (red) pole on the switch has lost some conductivity.

Looking at my attached image, (with the switch I believe to be in the off position) I can only assume, that off creates a short across the red and yellow wires, which cancels out the coil in the diaphram, only in my case, it's not quite working.

 

[Harald Kapp]

Looking at my attached image, (with the switch I believe to be in the off position) I can only assume, that off creates a short across the red and yellow wires, which cancels out the coil in the diaphram,

Looks like the most reasonable explanation. The wire attached to the case of the switch would be ground to achieve a kind of shielding through the metal case of the switch.

only in my case, it's not quite working.

Easy to check with the microphone disconnected and an Ohmmeter (multimeter in Ohm setting) across the two pins. They should show open in the microphone switch's on position and a short circuit in the switch's off position. As an additional protection for the diaphragm you can disconnect the diaphragm from the switch before measuring (just to make sure the DC voltage from the Ohmmeter doesn't any damage).

If the assumption turns out correct, it's a matter of finding a replacement switch.

 

[Martaine2005]

if i shout loudly in to it and turn up the volume on the amp, i can still hear input from the mic.

Perhaps when the active circuit is off, the mic itself still works to a certain degree passively?. Which is why you need to shout loudly?.
Poor design?.
A little like a headphone working as a mic.

Martin

 

[DJL33B]

When the switch is 'Off', the contacts close and suppress the signal. If you can still hear the sound through the amp it means the switch contacts may be worn or dirty. Contact cleaner may help.

 

[BobK]

Perhaps when the active circuit is off, the mic itself still works to a certain degree passively?. Which is why you need to shout loudly?.
Poor design?.
A little like a headphone working as a mic.

Martin

This is a likely a dynamic mike with no active circuitry.

The switch is shorting the mike output.

Most likely dirty contacts as someone else stated.

Bob

 

[hevans1944]

...When i switch it off, the diaphram is still active, but not fully active.
Over a period of a few seconds, the input fades away...

I like the explanations about faulty switch contacts not fully shorting the output of the microphone. But where does the delay "over a period of a few seconds" between operating the switch and input fading away occur? The fact that cranking up the volume on your amplifier while shouting into the microphone yields sound you can hear makes sense for either an electret or moving-coil (or ribbon) dynamic microphone... but the delay is a mystery.

So why do you care about this anomalous performance from a karaoke microphone? Turn the switch off when changing performers AND turn the volume down on the amplifier? Presumably there is an MC (master of ceremonies) supervising the karaoke performances, introducing each singer, controlling the microphone and the amplifier, etc. Maybe the MC could turn the volume up and down on the amplifier between performers?

 

[Audioguru]

Cheap switches like that have silver contacts so that they can pass come current. What happens to silver? It corrodes and turns black but high current burns off the corrosion and no problem.
A microphone does not produce a high current so the corrosion prevents the switch from shorting away the audio.
I always use switches with gold plated contacts that are made for these low level audio circuits. Gold never corrodes. The gold is thin and has a fairly low maximum current rating so the gold switch costs the same as a silver switch.