help!!!with capacitor values for phantom power

[nandax]

as u guys see in the schematic I would like to powering the electret microphone
and connected to mic pre amps, and the mic pre amp has input impedance of 47 Kohm,
because the microphone has XLR connector, I connect the pin 2 in series with c1 before it goes to input of pre amp;
my question is if i put 6.8uF capacitor in series, would it be high pass filter? because the input impedance of mic pre amp (m040 pre amp) 47k, so the cut off frequency will be 0.5 Hz?
will it be ok? because the Frequency range of pre amp: approx. 10 Hz...100 kHz
do i have to use same value of capacitor for pin 3?

thanks..

 

[duffy]

Yes, it's a high-pass filter - but that electret doesn't seem to be wired right. 3-pin electrets usually have a separate supply, ground and output.

 

[nandax]

Yes, it's a high-pass filter - but that electret doesn't seem to be wired right. 3-pin electrets usually have a separate supply, ground and output.

I just look from the schematic Phantom power feeding unit for microphone in
Powering microphones

 

[Nigel Goodwin]

I just look from the schematic Phantom power feeding unit for microphone in
Powering microphones

Phantom power isn't for feeding electret inserts, it's for feeding condensor mikes - and is usually 48V.

This is why it connects to an XLR socket.

What type of microphone are you using, and what are you trying to do with it?.

 

[nandax]

Phantom power isn't for feeding electret inserts, it's for feeding condensor mikes - and is usually 48V.

This is why it connects to an XLR socket.

What type of microphone are you using, and what are you trying to do with it?.

i am using **broken link removed**
this microphone

 

[Nigel Goodwin]

OK, so it's a proper mike, not just an insert.

So you need proper phantom power, and I would suggest you make the preamp a balanced one as well. You might have a look at:

**broken link removed**

Or here:

**broken link removed**

 

[nandax]

OK, so it's a proper mike, not just an insert.

So you need proper phantom power, and I would suggest you make the preamp a balanced one as well. You might have a look at:

**broken link removed**

Or here:

**broken link removed**

the preamp i used is M040
do u think it is ok?

 

[Nigel Goodwin]

the preamp i used is M040
do u think it is ok?

No, it's not very suitable, you really need a balanced preamp with a fairly low impedance input.

 

[nandax]

No, it's not very suitable, you really need a balanced preamp with a fairly low impedance input.

but it worked before, I put c1 and c2 6.8uF, the problem is when i connect it to the amplifier circuit and to the speaker and there is also noise there,
thats why i wonder if it is because the value of capacitor is not right?

 

[Nigel Goodwin]

but it worked before, I put c1 and c2 6.8uF, the problem is when i connect it to the amplifier circuit and to the speaker and there is also noise there,
thats why i wonder if it is because the value of capacitor is not right?

The capacitors won't introduce noise - but the resistors feeding the phantom power are also feeding the PSU noise directly in to the input of the amplifier. By using a proper impedance balanced amplifier this is cancelled out.

 

[nandax]

The capacitors won't introduce noise - but the resistors feeding the phantom power are also feeding the PSU noise directly in to the input of the amplifier. By using a proper impedance balanced amplifier this is cancelled out.

but the impedance from microphone is 300 ohms,
and the pre amp input impedance is about 47k ohms, so it is impedance bridging right?
so i think the impedance value is ok right?

 

[Nigel Goodwin]

but the impedance from microphone is 300 ohms,
and the pre amp input impedance is about 47k ohms, so it is impedance bridging right?
so i think the impedance value is ok right?

No, 47k is far too high - something like 4.7K or less would be usually for a low impedance mike input. But been phantom powered it's important that the preamp is balanced, otherwise you're just feeding noise to the input.

 

[nandax]

No, 47k is far too high - something like 4.7K or less would be usually for a low impedance mike input. But been phantom powered it's important that the preamp is balanced, otherwise you're just feeding noise to the input.

but in impedance bridging Z load >> Zsource right?
thats why i though the impedance of pre amp>> than mic impedance,
do u know how to feed the input from balance mic with phantom supply to unbalance pre amp ?

 

[Nigel Goodwin]

but in impedance bridging Z load >> Zsource right?
thats why i though the impedance of pre amp>> than mic impedance,

Yes, but you want around five to ten times the impedance, not hundreds. A preamp with 47K input will have a far lower gain and probably more noise.

do u know how to feed the input from balance mic with phantom supply to unbalance pre amp ?

Yes, you place a preamp with a balanced input between them - or you could use a microphone transformer, assuming it's balanced/unbalanced.

 

[nandax]

Yes, but you want around five to ten times the impedance, not hundreds. A preamp with 47K input will have a far lower gain and probably more noise.



Yes, you place a preamp with a balanced input between them - or you could use a microphone transformer, assuming it's balanced/unbalanced.

so is it because the input impedance too high, the noise occurs in the output?
because i Use the +12 volt voltage supply from PC

 

[Nigel Goodwin]

so is it because the input impedance too high, the noise occurs in the output?
because i Use the +12 volt voltage supply from PC

Partially, but mostly because you aren't using a balanced input - as I keep telling you. You're feeding power supply noise directly in the input of the amplifier.

 

[nandax]

Partially, but mostly because you aren't using a balanced input - as I keep telling you. You're feeding power supply noise directly in the input of the amplifier.

now i am using dynamic microphone, with Xlr connector also, and i would like to connect it to GSm modem. it has microphone + and microphone - connection, and i amplify the signal by connect the microphone to mic pre amp (kemo M040)
the connection like in the schematic..
but when i tried too call the modem, i can hear the voice from the mic, but also a lot of noise there
is there any suggestion to get rid of that noise?

 

[Nigel Goodwin]

If it has a microphone input, why are you using a preamp?.

 

[nandax]

If it has a microphone input, why are you using a preamp?.

because i tried connected directly o microphone input , and I could not hear anything,
I ever tested it with the microphone from handset and it works.
that s why i think it might be because of the signal from dynamic microphone is not loud enough

 

[audioguru]

The Kemo preamp does not have a low impedance balanced input but it might work if the dynamic mic is connected with a short length of shielded audio cable.