2 wire electret vs 3 wire

[pil]

My electret mic has only two wires. I saw a amplifier ciruict for a electret
which has 3 wires. the circuit consists of a LM741 opamp and a 2N2222
transistor. Can I use a two wire electret? what is the difference?

 

[John Fields]

On Tue, 13 Jul 2004 23:15:37 +0200, "pil" <pil@webmail.co.za> wrote:

My electret mic has only two wires. I saw a amplifier ciruict for a electret
which has 3 wires. the circuit consists of a LM741 opamp and a 2N2222
transistor. Can I use a two wire electret? what is the difference?

---
The short answer is yes, it can be done. The long answer is:
Why don't you post the circuit diagram so we can see what you're
talking about?

--
John Fields

 

[mlf]

In article <ROudnckVWdmczGndRVn-ig@is.co.za>, pil@webmail.co.za says...

My electret mic has only two wires. I saw a amplifier ciruict for a electret
which has 3 wires. the circuit consists of a LM741 opamp and a 2N2222
transistor. Can I use a two wire electret? what is the difference?



I am going to venture a guess that the body of the mic is ground.

In fact, I would make C1 an electrolytic 4.7uf and hook up this path:
+5 -> red wire -> -o- black/white wire -> +4.7 -> amp input.

 

[John Fields]

On Thu, 15 Jul 2004 05:43:11 GMT, mlf <vze1@verizon.net> wrote:

In article <ROudnckVWdmczGndRVn-ig@is.co.za>, pil@webmail.co.za says...
My electret mic has only two wires. I saw a amplifier ciruict for a electret
which has 3 wires. the circuit consists of a LM741 opamp and a 2N2222
transistor. Can I use a two wire electret? what is the difference?



I am going to venture a guess that the body of the mic is ground.
In fact, I would make C1 an electrolytic 4.7uf and hook up this path:
+5 -> red wire -> -o- black/white wire -> +4.7 -> amp input.

---
I'm going to venture a guess that you're wrong:


+V
|
[3K]
+-----+ |
| BIAS|--+--[+10ľF]--->AUDIO OUT
| |
| GND|--------------->GND
+-----+


--
John Fields

 

[Watson A.Name \"Watt Sun]

John Fields wrote:

On Thu, 15 Jul 2004 05:43:11 GMT, mlf <vze1@verizon.net> wrote:

In article <ROudnckVWdmczGndRVn-ig@is.co.za>, pil@webmail.co.za
says...

My electret mic has only two wires. I saw a amplifier ciruict for
a electret which has 3 wires. the circuit consists of a LM741
opamp and a 2N2222 transistor. Can I use a two wire electret?
what is the difference?

I am going to venture a guess that the body of the mic is ground.
In fact, I would make C1 an electrolytic 4.7uf and hook up this
path: +5 -> red wire -> -o- black/white wire -> +4.7 -> amp input.

--- I'm going to venture a guess that you're wrong:

--->AUDIO OUT | | |
GND|--------------->GND +-----+

THis would be okay as long as the right side of the electrolytic is
connected to a voltage lower than the left side. But the problem is
what is the voltage on the right side? If it's higher than the left
side, then the electrolytic will be reversed. This could happen if the
audio out is connected to the input of the opamp which is biased at half
the supply votlage. One solution would be to use a non-polarized cap.
Another is to use two 'lytics in series, and connect the neg's together,
and thru a 100k resistor to ground.