help in a mic preamp

[audioguru]

43 ohms needs a peak current of about 70mA to be loud in an earphone. A TL07x opamp has a max peak output of about 20mA so it will sound less loud and will severely distort if the volume is turned up.

 

[wakeke]

we can't get it to drive the headphones. we've been changing the values of the resistors, and the Vcc but we get no favorable output.
we changed the TL074 to a LM741 but still no output...
the mic preamp is working.

 

[audioguru]

Because you saved your schematic as a fuzzy JPG file type instead of as a very clear GIF or PNG file type, I cannot see the pins numbers on the mixer opamp.

You should remove the volume control R21 from the output. Maybe it is burned out.

 

[wakeke]

here's the summing/mixer circuit as PNG...the mic preamp circuit is the same...

 

[audioguru]

Your schematic will be correct when you remove the R23 and R24 pots.

 

[wakeke]

Your schematic will be correct when you remove the R23 and R24 pots.

however, how can we control the left and right output if we don't have a balance?

thanks!

 

[Nigel Goodwin]

however, how can we control the left and right output if we don't have a balance?

It's only mono, why you want to alter the levels?.

 

[elnino86]

hi wakake,what software are you using to simulate your circuit?

 

[wakeke]

hi wakake,what software are you using to simulate your circuit?

I'm using Multisim 9...

 

[wakeke]

It's only mono, why you want to alter the levels?.

yeah, it's mono, got the wrong construction for summing/mixing...the 2 mic preamps are separated and will be summed to other audio preamps for the channels (left & right)...

will change the schematic for it...thanks!


by the way...Merry Xmas to all (for those who celebrate it)...

 

[wakeke]

got the mic preamp to work using dynamic mic (w/ a batt.) but if used with non-batt. dynamic mic, it doesn't produce sound,...would it be the supply voltage too low for a dynamic mic? thanks! & merry Xmas!

 

[audioguru]

got the mic preamp to work using dynamic mic (w/ a batt.) but if used with non-batt. dynamic mic, it doesn't produce sound,...would it be the supply voltage too low for a dynamic mic? thanks! & merry Xmas!

A dynamic mic does not need power. R1 in your circuit should be removed.
A dynamic mic is a moving coil in a magnet exactly like a tiny speaker and it generates a signal.

An electret mic has a FET transistor inside that is powered from R1 in your circuit. Your circuit is wired for a 2-wires electret mic and must be changed if you use a 3-wires electret mic.
Some electret mics have their own battery for power and then R1 in your circuit should be removed.

 

[wakeke]

A dynamic mic does not need power. R1 in your circuit should be removed.
A dynamic mic is a moving coil in a magnet exactly like a tiny speaker and it generates a signal.

ok, will try to remove R1...we thought that a dynamic mic lacks supply in power from our circuit because there's no sound being produced and then we tried one with an internal batt. in it and it worked...

An electret mic has a FET transistor inside that is powered from R1 in your circuit. Your circuit is wired for a 2-wires electret mic and must be changed if you use a 3-wires electret mic.
Some electret mics have their own battery for power and then R1 in your circuit should be removed.

we're using a 2-wired electret mic & it did need power from the previous trials...but in the end we will use dynamic mic for this amplifier project...

Thanks! Merry Xmas

 

[wakeke]

just to clear it up...removing R1, so there's still be a connection between the supply and the dynamic mic? specifically the positive of the mic?...

 

[audioguru]

just to clear it up...removing R1, so there's still be a connection between the supply and the dynamic mic? specifically the positive of the mic?...

I don't know what you are talking about. A mic is never connected to a supply voltage. A dynamic mic is a coil of wire. It will burn if it is connected to the supply.
An electret mic is powered through a 10k resistor.

Here is the way both mics are connected to your preamp:

 

[wakeke]

I don't know what you are talking about. A mic is never connected to a supply voltage. A dynamic mic is a coil of wire. It will burn if it is connected to the supply.
An electret mic is powered through a 10k resistor.

Here is the way both mics are connected to your preamp:

tried that one w/ the dynamic mic but no sound came out...

 

[audioguru]

Maybe you burned out your dynamic mic by connecting it to the power supply. Measure its resistance. It should be about 250 ohms.

A dynamic mic has an output of 10mV RMS when you closely talk to it.
The opamp has a max gain of 101 so its output is 1.01V RMS.
The opamp is not strong enough to drive a speaker nor headphones.

 

[wakeke]

no,we didn't burn out the dynamic mic..

still working when connected to an audio component..

about 550ohms..

 

[audioguru]

Your preamp is also an audio component. The dynamic mic should have worked there too.

 

[wakeke]

yeah, it should have,but it didn't