Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Problem with electret mic and a circuit that powers it

Status
Not open for further replies.

danesh

Full Member level 3
Joined
Nov 24, 2003
Messages
186
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
1,365
loading on electret mic

i have design a circuit which would be bidirectional. This path would be used to flow the receive and transmit audio signal and also would used to power um my electret mic. I have notice whn i connect elektret mic to this line the signal ac level reduce. Can any one help me
 

paulux

Advanced Member level 4
Joined
May 16, 2005
Messages
112
Helped
11
Reputation
22
Reaction score
2
Trophy points
1,298
Activity points
2,339
Re: loading on electret mic

THe mic can be modeled as small equivalent resistor and capacitor so it loads your circuits. You may try to use resistor to bias the mic and then ac-coupled the mic signal for further processing.
 

xxargs

Full Member level 4
Joined
Jul 28, 2002
Messages
229
Helped
44
Reputation
88
Reaction score
2
Trophy points
1,298
Activity points
4,642
Re: loading on electret mic

danesh said:
i have design a circuit which would be bidirectional. This path would be used to flow the receive and transmit audio signal and also would used to power um my electret mic. I have notice whn i connect elektret mic to this line the signal ac level reduce. Can any one help me


Your electret mic loads (heavy) your signal-bus and is difficult to make solution in easy way...

- telegraph and telephone industrie try this solution in beginning of 1900 and need find out to make workarounds ;-)

In most case you need Low noise OP-amp with recommend impedances for best response and lowest noise from your mic and, isolate your common LF-bus to NOT feeding mic with ac-signal from other sources on your bus...

---

I don't know your topology, but bidirectional soloution (on 2-wire) is always tricky to make good and most case including fork or hybrid circurits to splitting up from 2-wire common bus to 4-wire in terminate side input/output (mic/earphone) and make good balace for good isolation between input and output (not hearing itself talking).


see litterature on telephone...
 

flatulent

Advanced Member level 5
Joined
Jul 19, 2002
Messages
4,629
Helped
489
Reputation
980
Reaction score
150
Trophy points
1,343
Location
Middle Earth
Activity points
46,689
Re: loading on electret mic

You can use active or passive hybrid circuits to split the two directional signals to two each two wire circuits. You have to be careful on the isolation of the two paths or you can get oscillations.

With the passive hybrid the termination of the fourth port in the line impedance has to use complex RC networks. One each R and C is not enough. Two each will drastically improve things.

Another option which is much cheaper for short cable runs is to use cables with two twisted pairs inside the outer jacket.
 

paulux

Advanced Member level 4
Joined
May 16, 2005
Messages
112
Helped
11
Reputation
22
Reaction score
2
Trophy points
1,298
Activity points
2,339
Re: loading on electret mic

Hi flatulent & xxargs,

Could you kindly provide schematics examples or reference documents of the circuit you described for further elaboration of the situation?

Thanks for your advices.
 

danesh

Full Member level 3
Joined
Nov 24, 2003
Messages
186
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,296
Activity points
1,365
Re: loading on electret mic

this would be my block diagram
 

xxargs

Full Member level 4
Joined
Jul 28, 2002
Messages
229
Helped
44
Reputation
88
Reaction score
2
Trophy points
1,298
Activity points
4,642
Re: loading on electret mic

flatulent said:
You can use active or passive hybrid circuits to split the two directional signals to two each two wire circuits. You have to be careful on the isolation of the two paths or you can get oscillations.

biggest problem in most case with active hybrid and gain on signal is make stability outside wanted bandwidth and frequence range, very easy to make oscillating around 10 - 20 kHz in situations 300 - 3400 Hz working very well...

With the passive hybrid the termination of the fourth port in the line impedance has to use complex RC networks. One each R and C is not enough. Two each will drastically improve things.

And bigger bandwidth, longer distance you need, your more complicate (higher orders) and more well tuned RC network (line ekvivalent) needs for still good isolation...

Another option which is much cheaper for short cable runs is to use cables with two twisted pairs inside the outer jacket.


I prefer last solution with separate mic and earphone/tx pair, but mic needs driver/buffer if distanse is more a few meters....

And cheap and possible screened Kat-5 cables working well for analog transmission.

With right drivers with complex C//R impedance out and terminate impedance, you can send 20 Hz - 20000 Hz pretty long way on CAT-5 cable without diskant loss.


/xxargs
 

paulux

Advanced Member level 4
Joined
May 16, 2005
Messages
112
Helped
11
Reputation
22
Reaction score
2
Trophy points
1,298
Activity points
2,339
Re: loading on electret mic

Is there any circuit including both mic & low noise amplifier? What considerations do we have when optimizing the noise of this system?
Any comments are welcomed. Thanks
 

xxargs

Full Member level 4
Joined
Jul 28, 2002
Messages
229
Helped
44
Reputation
88
Reaction score
2
Trophy points
1,298
Activity points
4,642
Re: loading on electret mic

paulux said:
Is there any circuit including both mic & low noise amplifier? What considerations do we have when optimizing the noise of this system?
Any comments are welcomed. Thanks


mic-amplifier inside cheap soundcard give more noise than elecret mic itself in many time (depend of very noise Power supply from computer). if you want high dynamic, you must have noise under control and possible rice to line level before transporting on long cable...

in Public adress-world using balanced line in most case to depress noise and inteference for mic and interconnection between equipment.

but if you only want S/N enougt for playing network game with headset, you not need spend time on high quality input...



xxargs
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top