Maker Pro
Maker Pro

condenser mics

J

Jamie

Jan 1, 1970
0
Are powered (2 wire, 3 volt average) condenser mic's noted for
losing their gain, producing crappie audio or both over time?

As I don't do that much repair work, I have some equipment
the owner states is producing low audio on TX. I can not see
anything wrong via the service monitor. So, i've deduced that
maybe the mic element is just producing crappie audio, which is a
2 wire powered condenser type in an standard HT dual band.. 150mhz&440Mhz.
What do you guys think?

P.S.
I don't have a real service manual for this unit, but I have
measured the injected deviation voltage at the varicaps of the
oscillators for the VHF and UHF.

They average around 200 mv PP via a normal audio conversation.

The modulation index seems to be correct on the service monitor.


http://webpages.charter.net/jamie_5"
 
Are powered (2 wire, 3 volt average) condenser mic's noted for
losing their gain, producing crappie audio or both over time?

I don't think they are noted for it but there are a few websites that
mention
charge leakage in electret microphones.

Some types of condensor microphone have active polarisation.
Electret microphones have charge trapped in a plastic film.

Here is a website with a comment saying
"It used to be that the charge would leak off in a few years, but that
has been solved. It also used to be that electret microphones were
inferior to externally polarized condenser microphones. That, too, is
no longer the case."
http://familyoralhistory.us/news/view/who_invented_the_electret_condenser_microphone/

I can't find it now but I vaguely recall reading somewhere that
condenser
microphones from the 1960's and 1970's may not work due to charge
leakage.

Radio transmitters generally have automatic gain control on the audio
so
a small drop in the microphone sensitivity should not make any
difference.

There might be other reasons for a microphone to produce bad sound
after
years such as the plastic film decaying or it being gunged up due
to being owned by a heavy smoker. I had a few bits of secondhand
radio equipment that stank due to being owned by smokers.

I expect some of the older people here who have been doing audio
for many years will have somthing to say on the subject.
You could try asking an audio group.

Bob
 
E

Eeyore

Jan 1, 1970
0
Jamie said:
Are powered (2 wire, 3 volt average) condenser mic's noted for
losing their gain, producing crappie audio or both over time?

These are 'electret mics' and not usually given the title condenser which is
reserved for a different construction and method of operation entirely.

And yes, early ones in particular are so noted to the extent of completely
losing output.. They will also do so if exposed to crappy environmental
conditions, especially humidity.

Graham
 
J

Jamie

Jan 1, 1970
0
I don't think they are noted for it but there are a few websites that
mention
charge leakage in electret microphones.

Some types of condensor microphone have active polarisation.
Electret microphones have charge trapped in a plastic film.

Here is a website with a comment saying
"It used to be that the charge would leak off in a few years, but that
has been solved. It also used to be that electret microphones were
inferior to externally polarized condenser microphones. That, too, is
no longer the case."
http://familyoralhistory.us/news/view/who_invented_the_electret_condenser_microphone/

I can't find it now but I vaguely recall reading somewhere that
condenser
microphones from the 1960's and 1970's may not work due to charge
leakage.

Radio transmitters generally have automatic gain control on the audio
so
a small drop in the microphone sensitivity should not make any
difference.

There might be other reasons for a microphone to produce bad sound
after
years such as the plastic film decaying or it being gunged up due
to being owned by a heavy smoker. I had a few bits of secondhand
radio equipment that stank due to being owned by smokers.

I expect some of the older people here who have been doing audio
for many years will have somthing to say on the subject.
You could try asking an audio group.

Bob

I purchased a electra 2 wire mic from the shaft and
will temporary solder it in to take measurements.

From what I can gather, it appears the audio is nasally sounding
and seems only to be responding at high output in a narrow portion
of the audio spectrum, this is taken from the element output.

I also noticed noise at the element that seems to me, excessive.

Thanks.


http://webpages.charter.net/jamie_5"
 
J

Jasen Betts

Jan 1, 1970
0
I purchased a electra 2 wire mic from the shaft and
will temporary solder it in to take measurements.

From what I can gather, it appears the audio is nasally sounding
and seems only to be responding at high output in a narrow portion
of the audio spectrum, this is taken from the element output.

I also noticed noise at the element that seems to me, excessive.

Thanks.

It it an electret or a condenser?
 
Top