Bob Cain wrote:
> 
> 
> Michel Rouzic wrote:
> 
>> Any suggestiongs for a $10 microphone?
> 
> 
> Radio Shack sells a small electret capsule for about a third of that 
> which is of surprisingly good quality.  It requires a resistor, a 
> capacitor a battery and a cable with 1/8" plug on it.  The simple 
> circuit diagram used to be printed on the package that it comes in.

He has no soldering iron :-(
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Michel Rouzic wrote:
> Jim Adamthwaite wrote:
> 
>>Michel Rouzic wrote:
>>
>>>Just wondering, how do you calculate the voltage multiplication out of
>>>the impedance of each part?
>>
>>The voltage multiplication ratio IS the turns ratio.  This is often not
>>on the label, but can be deduced.
>>
>>As a first approximation, the load impedance which you connect to the
>>output of the transformer determines how much load-side current which
>>will flow for a given output signal.  (Ohm's law: I=E/R).
>>
>>In our step up example, The input (mike) voltage will be 1/25th of the
>>output voltage, and the input current drawn from the mike MUST be 25
>>times higher than the output load current (for power in & out to be the
>>same).
>>
>>The transformer input will therefore look (from the mike's point of
>>view) like a load with an impedance of 1/625th ( 1/(25*25) ) of
>>whatever load you connect to the output.
>>
>>So the impedance ratio is the square of the turns ratio.  If you know
>>the rated i/p & o/p Z's, the turns ratio (N) is:  N = sqrt( Zs / Zp)
>>
>>If you vary the load you connect to the output, the input impedance will
>>vary proportionally.
>>
>>Transformers do not have a fixed impedance, the manufacturer is just
>>specifying the design-centre range for optimal performance.
>>
>>
>>
>>>Anyways I guess a 230 to 12 volt (or less) transformer will do it,
>>
>>right?
>>
>>Yes, a mains transformer will do fine for voice quality.  Treble
>>response will probably be dropping before you reach 20KHz due to high
>>inter-turn secondary winding self-capacitance.
>>
>>As the mike signal power is so low you need not concern yourself about
>>core non-linearity issues.
>>
>>A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy
>>experimentation.
>>
>>BTW, does your sound card have a microphone (high gain) input?
> 
> 
> yes it does and that's what i'm using, but because I need to amplify it
> to the maximum I get lots of noise.
> 
> However i just realized that my soldering iron is dead (doesn't warm up
> and testing the two power connectors's resistance show no conductivity)
> and that i have the choice between either investing in a new one as I
> use it like once every three years, otherwise buy a $10 microphone.
> 
> Any suggestiongs for a $10 microphone?

http://jameco.com/webapp/wcs/stores/servlet/CatalogSearchResultView?langId=-1&storeId=10001&catalogId=10001&searchType=k&searchValue=microphone&categoryId=504510
http://jameco.com/webapp/wcs/stores/servlet/CatalogSearchResultView?langId=-1&storeId=10001&catalogId=10001&searchType=k&searchValue=microphone&categoryId=504520
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Michel Rouzic wrote:
> Jim Adamthwaite wrote:
> 
>>Michel Rouzic wrote:
>>
>>>Just wondering, how do you calculate the voltage multiplication out of
>>>the impedance of each part?
>>
>>The voltage multiplication ratio IS the turns ratio.  This is often not
>>on the label, but can be deduced.
>>
>>As a first approximation, the load impedance which you connect to the
>>output of the transformer determines how much load-side current which
>>will flow for a given output signal.  (Ohm's law: I=E/R).
>>
>>In our step up example, The input (mike) voltage will be 1/25th of the
>>output voltage, and the input current drawn from the mike MUST be 25
>>times higher than the output load current (for power in & out to be the
>>same).
>>
>>The transformer input will therefore look (from the mike's point of
>>view) like a load with an impedance of 1/625th ( 1/(25*25) ) of
>>whatever load you connect to the output.
>>
>>So the impedance ratio is the square of the turns ratio.  If you know
>>the rated i/p & o/p Z's, the turns ratio (N) is:  N = sqrt( Zs / Zp)
>>
>>If you vary the load you connect to the output, the input impedance will
>>vary proportionally.
>>
>>Transformers do not have a fixed impedance, the manufacturer is just
>>specifying the design-centre range for optimal performance.
>>
>>
>>
>>>Anyways I guess a 230 to 12 volt (or less) transformer will do it,
>>
>>right?
>>
>>Yes, a mains transformer will do fine for voice quality.  Treble
>>response will probably be dropping before you reach 20KHz due to high
>>inter-turn secondary winding self-capacitance.
>>
>>As the mike signal power is so low you need not concern yourself about
>>core non-linearity issues.
>>
>>A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy
>>experimentation.
>>
>>BTW, does your sound card have a microphone (high gain) input?
> 
> 
> yes it does and that's what i'm using, but because I need to amplify it
> to the maximum I get lots of noise.
> 
> However i just realized that my soldering iron is dead (doesn't warm up
> and testing the two power connectors's resistance show no conductivity)
> and that i have the choice between either investing in a new one as I
> use it like once every three years, otherwise buy a $10 microphone.
> 
> Any suggestiongs for a $10 microphone?

http://jameco.com/webapp/wcs/stores/servlet/CatalogSearchResultView?langId=-1&storeId=10001&catalogId=10001&searchType=k&searchValue=microphone&categoryId=504510

-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Michel Rouzic wrote:

> Any suggestiongs for a $10 microphone?

Radio Shack sells a small electret capsule for about a third of that 
which is of surprisingly good quality.  It requires a resistor, a 
capacitor a battery and a cable with 1/8" plug on it.  The simple 
circuit diagram used to be printed on the package that it comes in.


Bob
-- 

"Things should be described as simply as possible, but no simpler."

                                              A. Einstein

Jim Adamthwaite wrote:
> Michel Rouzic wrote:
> >
> > Just wondering, how do you calculate the voltage multiplication out of
> > the impedance of each part?
>
> The voltage multiplication ratio IS the turns ratio.  This is often not
> on the label, but can be deduced.
>
> As a first approximation, the load impedance which you connect to the
> output of the transformer determines how much load-side current which
> will flow for a given output signal.  (Ohm's law: I=E/R).
>
> In our step up example, The input (mike) voltage will be 1/25th of the
> output voltage, and the input current drawn from the mike MUST be 25
> times higher than the output load current (for power in & out to be the
> same).
>
> The transformer input will therefore look (from the mike's point of
> view) like a load with an impedance of 1/625th ( 1/(25*25) ) of
> whatever load you connect to the output.
>
> So the impedance ratio is the square of the turns ratio.  If you know
> the rated i/p & o/p Z's, the turns ratio (N) is:  N = sqrt( Zs / Zp)
>
> If you vary the load you connect to the output, the input impedance will
> vary proportionally.
>
> Transformers do not have a fixed impedance, the manufacturer is just
> specifying the design-centre range for optimal performance.
>
>
> > Anyways I guess a 230 to 12 volt (or less) transformer will do it,
> right?
>
> Yes, a mains transformer will do fine for voice quality.  Treble
> response will probably be dropping before you reach 20KHz due to high
> inter-turn secondary winding self-capacitance.
>
> As the mike signal power is so low you need not concern yourself about
> core non-linearity issues.
>
> A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy
> experimentation.
>
> BTW, does your sound card have a microphone (high gain) input?

yes it does and that's what i'm using, but because I need to amplify it
to the maximum I get lots of noise.

However i just realized that my soldering iron is dead (doesn't warm up
and testing the two power connectors's resistance show no conductivity)
and that i have the choice between either investing in a new one as I
use it like once every three years, otherwise buy a $10 microphone.

Any suggestiongs for a $10 microphone?

On Sat, 25 Feb 2006 14:44:13 +1100, Allan Herriman
<allanherriman@hotmail.com> wrote:

[snip]
>You probably should be using a tiny audio transformer, rather than a
>mains transformer.
>Radio Shack (or their equivalent in your part of the world) should
>have these in stock.
>
>Look at part 237-1146-ND from digikey:
>http://dkc3.digikey.com/PDF/T061/1619.pdf
>You could shop around and find an equivalent transformer for one
>hundredth  the price.

... or even cheaper if you pull one out of a 1970s style transistor
radio.

Regards,
Allan

Mark wrote:
> why are you trying to use a speaker as a mic
>
> a speaker makes a terrible mic
>
> get a cheap radio shack condensor mic with a built in prepamp...it will
> work 1000% better than any speaker
>
> most comouter "mic" inputs are designed to supply a small DC voltage
> for these condensor mics so you will be all set to go...
>
> (P.S. I'm not talking about +48 so called phantom power used in
> professional audio gear)

Maybe it makes a terrible mic, but that's all I had under the hand, and
the advantage is since it came by two I could use one as a speaker and
the other as a mic in order to calibrate the two.

No radio shack around here, and I'm not going to town very often
anyways, so I really better count on what I already have.

why are you trying to use a speaker as a mic

a speaker makes a terrible mic

get a cheap radio shack condensor mic with a built in prepamp...it will
work 1000% better than any speaker

most comouter "mic" inputs are designed to supply a small DC voltage
for these condensor mics so you will be all set to go...

(P.S. I'm not talking about +48 so called phantom power used in
professional audio gear)


Mark

Michel Rouzic wrote:
> 
> Just wondering, how do you calculate the voltage multiplication out of
> the impedance of each part?

The voltage multiplication ratio IS the turns ratio.  This is often not
on the label, but can be deduced.

As a first approximation, the load impedance which you connect to the
output of the transformer determines how much load-side current which
will flow for a given output signal.  (Ohm's law: I=E/R).

In our step up example, The input (mike) voltage will be 1/25th of the
output voltage, and the input current drawn from the mike MUST be 25
times higher than the output load current (for power in & out to be the
same).

The transformer input will therefore look (from the mike's point of
view) like a load with an impedance of 1/625th ( 1/(25*25) ) of
whatever load you connect to the output.

So the impedance ratio is the square of the turns ratio.  If you know
the rated i/p & o/p Z's, the turns ratio (N) is:  N = sqrt( Zs / Zp)

If you vary the load you connect to the output, the input impedance will
vary proportionally.

Transformers do not have a fixed impedance, the manufacturer is just
specifying the design-centre range for optimal performance.


> Anyways I guess a 230 to 12 volt (or less) transformer will do it,
right?

Yes, a mains transformer will do fine for voice quality.  Treble
response will probably be dropping before you reach 20KHz due to high
inter-turn secondary winding self-capacitance.

As the mike signal power is so low you need not concern yourself about
core non-linearity issues.

A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy
experimentation.

BTW, does your sound card have a microphone (high gain) input?

Jim A.

Michel Rouzic wrote:

   ...

> Just wondering, how do you calculate the voltage multiplication out of
> the impedance of each part? Anyways I guess a 230 to 12 volt (or less)
> transformer will do it, right?

The voltage ratio is equal to the turns ratio. The impedance ratio is 
the square of that. You want an audio transformer for best results. A 
power transformer will be lossier at high frequencies.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������