Max ratings of electret mic

[pimpom]

Can anyone please give me an idea of the maximum safe P.S.
voltage of the ubiquitous cheap electret microphone used in
portable recorders, cheap headphones-mic combos, lapel mikes,
etc.? I mean those that have a built-in FET buffer/amplifier and
are generally used with a P.S of 5V or less. TIA.

 

[Phil Allison]

"pimpom"

Can anyone please give me an idea of the maximum safe P.S. voltage of the
ubiquitous cheap electret microphone used in portable recorders, cheap
headphones-mic combos, lapel mikes, etc.? I mean those that have a
built-in FET buffer/amplifier and are generally used with a P.S of 5V or
less. TIA.

** See: http://en.wikipedia.org/wiki/Electret_microphone

See the schematic - it shows a resistor in series with the FET which MUST
be there for it to work.

The supply voltage can be anything from 1.5 volts up to 12 volts, depending
on the particular capsule while the resistor can be from 2.2kohms up to
10kohms.

The voltage appearing across the FET will be half or less than the supply
voltage.



...... Phil

 

[pimpom]

"pimpom"


** See: http://en.wikipedia.org/wiki/Electret_microphone

See the schematic - it shows a resistor in series with the FET
which MUST be there for it to work.

The supply voltage can be anything from 1.5 volts up to 12
volts, depending on the particular capsule while the resistor
can be from 2.2kohms up to 10kohms.

The voltage appearing across the FET will be half or less than
the supply voltage.

Thanks for the reply. I understand the principles and I already
looked up some catalogs, but none specified the max P.S. voltage.
What I wanted to know was whether it would be safe (for the FET)
to operate the microphone at something like 9-12V. I guessed it
would be, but wanted confirmation.

I expected that, like you said, the max ratings would differ for
different models. But just as it would be unusual for a
general-purpose low-power BJT to have a max Vce rating of less
than 20V, I hoped that someone would be able to cite some voltage
that could be expected to not exceed the max Vds rating of the
vast majority of electret mikes.

 

[pimpom]

"pimpom"


** See: http://en.wikipedia.org/wiki/Electret_microphone

See the schematic - it shows a resistor in series with the FET
which MUST be there for it to work.

The supply voltage can be anything from 1.5 volts up to 12
volts, depending on the particular capsule while the resistor
can be from 2.2kohms up to 10kohms.

The voltage appearing across the FET will be half or less than
the supply voltage.

Thanks for the reply. I understand the principles and I already
looked up some catalogs, but none specified the max P.S. voltage.
What I wanted to know was whether it would be safe (for the FET)
to operate the microphone at something like 9-12V. I guessed it
would be, but wanted confirmation.

I expected that, like you said, the max ratings would differ for
different models. But just as it would be unusual for a
general-purpose low-power BJT to have a max Vce rating of less
than 20V, I hoped that someone would be able to cite some voltage
that could be expected to not exceed the max Vds rating of the
vast majority of electret mikes.

 

[Phil Allison]

"pimpom"

"Phil Allison"
Thanks for the reply. I understand the principles and I already looked up
some catalogs, but none specified the max P.S. voltage. What I wanted to
know was whether it would be safe (for the FET) to operate the microphone
at something like 9-12V. I guessed it would be, but wanted confirmation.

I expected that, like you said, the max ratings would differ for different
models. But just as it would be unusual for a general-purpose low-power
BJT to have a max Vce rating of less than 20V, I hoped that someone would
be able to cite some voltage that could be expected to not exceed the max
Vds rating of the vast majority of electret mikes.

** Err - you just completely changed the nature of your question.

P.S. voltage is one thing, max Vds of the FET is another.

The whole point is that there IS a current limiting resistor - and if
the PS voltage goes up, the SO must the value of that resistor.

Plus - what the **** are you on about ????

Your dopey Q simply has no context.

Just like you.




...... Phil

 

[pimpom]

"pimpom"


** Err - you just completely changed the nature of your
question.

P.S. voltage is one thing, max Vds of the FET is another.

Why? Since the electret itself is tied to gate and source, the
limiting voltage is the max Vds of the FET. Sure, the load
resistor drops some of the supply voltage, but by how much is not
precisely predictable. The FET charcteristics are unknown; and
even if typical values are given, there are tolerances - often as
much as +/-50% for Idss. Then there's the swing from steady-state
when there's an input. That swing may be of the order of
millivolts under normal signal conditions, but there could be
circumstances, intended or unintended, where the swing is much
more, theoretically up to the P.S. voltage.

The whole point is that there IS a current limiting
esistor - and if the PS voltage goes up, the SO must the
value of that resistor.

In typical applications, yes. But what if I or someone else want
to use the unit in an Atypical application? For example, I may
want to keep circuit component count to a minimum by supplying
the mic directly from a convenient, well filtered supply of +20V,
but, for some reason, also want to keep the load resistor low. Or
even use an inductive load. The max Vds (and possibly
dissipation) rating will then be the ultimate limiting factor.

Plus - what the **** are you on about ????

See above.

Your dopey Q simply has no context.

Just like you.

That was uncalled for. But I'll take it in the spirit of Usenet
and just shrug.

 

[Phil Allison]

"pimpom"

"Phil Allison"

Why?

** Because there is a resistor between the damn PS and the FET !!!!

The numbers are not the same nor simply related.


(snip more mind numbing drivel)

In typical applications, yes.

** Err - like ones that actually work ??

But what if I or someone else want to use the unit in an Atypical
application?

** The YOU spell it out for us - fuckwit.

See above.

** Pure lunacy.

That was uncalled for. But I'll take it in the spirit of Usenet and just
shrug.

** Piss off - you ridiculous WANKER !!



....... Phil

 

[pimpom]

"pimpom"


** Because there is a resistor between the damn PS and the FET
!!!!

The numbers are not the same nor simply related.


(snip more mind numbing drivel)

I can't believe that you don't know the difference between limits
imposed by voltage and that by current.

** Err - like ones that actually work ??

Can't you imagine using a device for anything other than its main
application? I can. Like using a screwdriver as a lever when
nothing else is available. It "actually works", you know. I just
take care to select the proper size.

** The YOU spell it out for us - fuckwit.

When someone asks you for directions to a place, do you demand
that he reveals everything he intends to do in that place? Maybe
*you* do at that. I simply asked if anyone knew the max voltage
rating. What I want to do with that information is my business. I
did NOT ask for help in designing something or if an electret mic
is suitable for a specific application. I simply asked for one
piece of information. If you don't know, shut the **** up. Moron.

** Pure lunacy.




** Piss off - you ridiculous WANKER !!

It's people like you who are driving others away from Usenet. And
yet you blame GG, newbies and anything else you can think of
except yourselves. Move your ass up out of your chair and go see
a shrink. You need some serious therapy.

 

[Phil Allison]

"pimpom"



** Piss off - you ridiculous FUCKING WANKER !!

 

[pimpom]

"pimpom"



** Piss off - you ridiculous FUCKING WANKER !!

You're repeating yourself. Yawwwn.
Can't think of any argument that makes sense, eh?

 

[Phil Allison]

"pimpom"

** Get fucked you vile little shit.

 

[pimpom]

"pimpom"

** Get fucked you vile little shit.

Oh, I do. All the time. OTOH, how long has it been since you got
laid - not couning those desperate homo sessions? A year?

You can congratulate yourself on one thing, though. Although
you're only the third person I've ever flamed over the internet,
you're the very first on whom I've ever used vulgar language. You
must have caught me in a good mood. Congratulations.