Electronic (electret?) replacement for crystal Microphone

[nina.p20]

I have several projects using the old crystal microphone.
I'd like suggestions how to change it to a more modern, electret or
cap. ones...
TIA
Nina

 

[John Woodgate]

I read in sci.electronics.design that nina.p20 <nina.p20@gmail.com>
wrote (in <1124171442.463015.187060@g14g2000cwa.googlegroups.com&gt about
'Electronic (electret?) replacement for crystal Microphone', on Mon, 15
Aug 2005:

I have several projects using the old crystal microphone.
I'd like suggestions how to change it to a more modern, electret or
cap. ones...
TIA
Nina

Electret is best. Cheap and quite good performance. You need to add a

simple op-amp with 20 to 40 dB gain, depending on what sensitivity of
the crystal mic your project designer assumed.

Of course, you don't need to feed the op-amp output into such a high
impedance as the crystal mic needed, but there is no need to modify that
input circuit unless you want to.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[nina.p20]

Thank you very much Mr. Woodgate.
As I need to work on very small devices, I have to use discreet
components, as transistors, and I *think* that the output has to have a
very high impedance...
As I'm new to newsgroups, I don't know if it's possible to attach a
schematic...
Regards,
Nina

 

[John Woodgate]

I read in sci.electronics.design that nina.p20 <nina.p20@gmail.com>
wrote (in <1124174322.044095.130160@z14g2000cwz.googlegroups.com&gt about
'Electronic (electret?) replacement for crystal Microphone', on Mon, 15
Aug 2005:

Thank you very much Mr. Woodgate.
As I need to work on very small devices, I have to use discreet
components, as transistors,

A discrete transistor amplifier will take up a LOT more room than an
op-amp.

and I *think* that the output has to have a
very high impedance...

No, it doesn't, unless the rest of your circuit uses a rather uncommon
technique (capacitive feedback or 'charge amplifier').

As I'm new to newsgroups, I don't know if it's possible to attach a
schematic...

It is possible to put 'ASCII-art' diagrams on this newsgroup, but real
graphics have to be put on alt.binaries.schematics.electronics.

I think you should tell us exactly what you are trying to do. It sounds
like a project beyond your current grasp of electronics. I say that not
to insult you but to prevent you being disappointed or even running into
really serious problems.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Don Lancaster]

nina.p20 wrote:

I have several projects using the old crystal microphone.
I'd like suggestions how to change it to a more modern, electret or
cap. ones...
TIA
Nina

The key rule is that an electret microphone requires a dc bias.
Typically +5 volts through a 3.3K resistor.


--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com