Electret mike - connection to plug

[atferrari]

I soldered the red/white wires to the mike's +/- terminals and the shield to the metalic housing.

A) At the plug end, the (-) and the shield were soldered together going to the common of the preamp. Is this reasonable?

B) Found the shielded plastic-jacketed bipolar cable quite hard to bend. Could I use single shielded wire (red only plus shield), soldering the shield to the housing and negative terminal? I do not see any difference since in both cases signal is unbalanced.

C) Used it to test on the bench my just-built pre + filter + amp. It seems to work but I hear some hum (most probably 50 Hz from mains). Should I do something else on the mike + wire + plug or could I expect that a metalic enclosure could cure it?

Thanks for any reply / comments.

 

[Mosaic]

perhaps this is useful:
http://recordinghacks.com/articles/how-to-build-a-microphone/

 

[atferrari]

Gracias for that, Mosaic.

 

[audioguru]

Most electret mics have 2-wires. The signal wire and the 0V shield wire. But your mic might have 3-wires (some are sold at Radio Shack).
The 3-wires electret mic has the red wire for the positive power to the mic, the white wire is the signal output wire and the shield wire shields the signal wire.

 

[atferrari]

AG, this is my electret: negative and signal. The next is a tab from the casing.

 

[audioguru]

Your electret mic has 3 wires. Your preamp is made for an electret mic that has only 2 wires.

An electret mic with 2 wires has its internal Jfet connected as common source. Its source pin connects to the 0V shield wire and metal case of the mic. The signal output wire connects to the drain pin of the Jfet. The load for the Jfet is provided by an external resistor (maybe 10k ohms) connected to about +9V.

An electret mic with 3 wires has the internal Jfet connected as common drain. Its drain pin (the red wire) connects to a positive voltage probably without a resistor. Its source pin is the output and might have an internal resistor to 0V. The shield wire connects to 0V and shields the signal output wire.

 

[atferrari]

Hola AG,

Mine has no continuity between casing and the (-) terminal.

When I grounded the casing through the shield what I heard was much more clear and free (almost) of hum or strange noises.

Just in case, I am using the preamp discussed in other thread, circuit posted by you many times and pinned by Nigel years ago.

 

[audioguru]

A voice electret mic usually has 2 wires. It works fine when the sound level is low but it causes distortion when the sound level is high.
An electret mic attached to a drum or musical instrument usually has 3 wires because the sound level is high.

Your mic can be connected and powered either way:
1) For 2 wires its case connects to the (-) terminal and the shield of the cable which connects to 0V at the preamp. The output is from the (+) terminal and is powered through a series load resistor from a positive power supply.

2) For 3 wires it uses a source resistor from its (-) terminal to its case. The case connects to the shield wire in the cable which connects to 0V at the preamp. The (+) terminal connects to a positive power supply. The output is from the (-) terminal.

 

[Mosaic]

Since this is very related I'll post in this thread.
audioguru: I got this item....but I am not sure about connecting it to a preamp, it appears to be a bare, 2 connection, condensor which requires a jfet type preamp circuit?

**broken link removed**

Thx.

 

[audioguru]

A "condenser" microphone without a datasheet and owner's manual is useless.
A real condenser mic needs a 48VDC bias voltage and a vacuum tube or Jfet very high impedance preamp.

An electret mic is a condenser mic that has the 48V built into the electret material. It also has a Jfet impedance converter inside.

 

[Mosaic]

I found this was quite interesting on amplifying such a condenser:
http://www.by-rutgers.nl/ME6211-PRO37R.html

and this venerable approach:
http://www.scotthelmke.com/alice-schematic.jpg

 

[audioguru]

The schematics do not show the 48V bias voltage and its filtering for the condenser mic.

 

[4pyros]

I found this was quite interesting on amplifying such a condenser:
http://www.by-rutgers.nl/ME6211-PRO37R.html

and this venerable approach:
http://www.scotthelmke.com/alice-schematic.jpg

You are way off!! the mics you got have to have 48 volt Phantom power to work at all. Not too simple for an inexperienced DIYer.
You would be much better off getting some mic's that don't need Phantom power.

 

[ronv]

Since they don't need much current you could probably "make" the 48 volts.

 

[Mosaic]

Um....I have the mic capsules, not the mics. Some condensers seem to work just fine on 10V.
We shall see what comes of the build. This circuit 'excites' the condenser with more V.

 

[4pyros]

Um....I have the mic capsules, not the mics. Some condensers seem to work just fine on 10V.
We shall see what comes of the build. This circuit 'excites' the condenser with more V.

Yours are rated for 48 Volts.
The circuit you posted does not make 48 volts, or even 10 volts.
Don't know what you are getting at.

 

[Mosaic]

This seems to provide the required polarizing voltage...what do you think?
**broken link removed**

 

[audioguru]

This seems to provide the required polarizing voltage...what do you think?
**broken link removed**

Do you have 25VAC to 30VAC available?

 

[ronv]

If you have say +12 available you could probably do it with a 555 voltage quadrupler. See what AG thinks.
It would save needing another supply.

 

[audioguru]

If you have say +12 available you could probably do it with a 555 voltage quadrupler. See what AG thinks.
It would save needing another supply.

It would be difficult to keep its frequency away from the mic audio.