microphone amplification with OPA134?

[whiz115]

i'm newbie and i want to build an amplified electret mic
can i use OPA134 to do that? thank you!

i want to experiment with op amps and i can't think a better way to use that IC.
if you can...recomend me some other uses.
the power supply i'm going to use is a lithium battery 3,6V 1300mA.

Thank you.

 

[Nigel Goodwin]

i'm newbie andi want to build an amplified electret mic
can i use OPA134 to do that? thank you!

Yes you can, and it's a nice low noise device.

 

[whiz115]

thank you for the fast answer!
can you recommend me something else...after finishing
my experiment?

 

[Nigel Goodwin]

Something else in what line?.

 

[whiz115]

it was intended to be used for a school practice on how to amplify weak signals...but i never used it. So i don't know what to do with it! it's specs are best suitable for audio...so probably something with audio?

btw...it didn't worked well with the electret...i heard my voice for 1-2 seconds and not very loud and then it stopped responding...i attached the following circuit to the OPA134 input pins...

O-----------/\/\/\-------||----O out+
|
3,6V @ mic
|
O-----------------------------O out-

what is wrong?

 

[Nigel Goodwin]

What's wrong is it's a jumbled collection of text! - use a paint package and draw the complete circuit, then we can comment on it.

 

[Hero999]

I hope you're not just planning to connect the out+/- to the inverting and non inverting pins of the OPA134; it won't work because you need some negitive feedback. Google op amp inverting amplifier.

 

[whiz115]

Nigel Goodwin i've made it in a hurry but it looks ok to my browser... anyway heres the circuit of what i connected...

Hero999 can you see the above drawing??

 

[audioguru]

No resistor value?
No capacitor value?
No OPA134 preamp circuit schematic with parts values?
No schematic showing the biased electret mic connected to the OPA134?
No load value for the opamp?

The minimum supply voltage for an OPA134 opamp is 5V, not 3.6V. Look at its datasheet. Maybe you forgot to power the opamp? Maybe you forgot to bias the opamp?

 

[whiz115]

No resistor value?
No capacitor value?
No OPA134 preamp circuit schematic with parts values?
No schematic showing the biased electret mic connected to the OPA134?
No load value for the opamp?

The minimum supply voltage for an OPA134 opamp is 5V, not 3.6V. Look at its datasheet. Maybe you forgot to power the opamp? Maybe you forgot to bias the opamp?

Hi! and thank you for you interest...

i thought that resistor and capacitor values are somewhat common...
anyway... to my case i'm using 1uF for the coupling capacitor and a 4K7 resistor which i had spare at the moment

the circuit goes directly to the input of the op amp...and there is no other circuit other than that of the electret.

i have read the manual of the op amp and it clearly says that the power supply range is from 2,5V to 18V.

@Hero999 from what i see from the manual there is no phase inversion to the OPA134...

 

[whiz115]

heres the link to the PDF... what am i doing wrong?

https://www.ti.com/lit/gpn/opa134

 

[audioguru]

The first page of the datasheet clearly shows that the supply voltage for the opamp is a minimum of plus and minus 2.5V which is 5V.

The opamp needs to be powered.
It needs to have its "+" input correctly biased.
It needs to have negative feedback to set its closed loop gain to a reasonal amount to avoid distortion.

This is how the preamp circuit should be connected:

 

[whiz115]

nice!!!

1) tell me...the R2,R3 what is for?
2) can i remove C4 if i use batteries?
3) R4 exists for the gain?

thanks again!

 

[Nigel Goodwin]

nice!!!

1) tell me...the R2,R3 what is for?

They bias the opamp to where it needs to be, effectively creating a 'split supply'.

2) can i remove C4 if i use batteries?

No, it's even more important for batteries - and should ALWAYS be included on any electronic project.

3) R4 exists for the gain?

The gain is set be the feedback resistors, one fixed, one adjustable.

 

[whiz115]

ok! now everything is very clear to me!
thank you all for contributing to my op amp lessons!

one last thing...what's going on between C1,R2,R3 and pin 3?
signal comes from C1 and we cross a DC??? what's the result?
a AC with bigger amplitude?

sorry if i'm saying nonsense...

 

[Nigel Goodwin]

I suggest you try googling for "opamp tutorial" or "741 tutorial", you will find plenty of sites that will teach you about opamps.

 

[audioguru]

R2 and R3 create a reference DC voltage for the opamp's pin 3 input that is half the supply voltage. Then the AC signal can swing the opamp's input an equal amount above it and below it. Then the opamp's output can swing equally above and below its resting DC voltage.

The opamp has a gain (amount of amplification) which is the ratio of the feedback resistors plus one.

 

[whiz115]

the AC signal can swing the opamp's input an equal amount above it and below it.

the weak AC voltage from the electret becomes half the power supply AC voltage and enters pin 3

that is what i understand... is it correct?

 

[audioguru]

the weak AC voltage from the electret becomes half the power supply AC voltage and enters pin 3

that is what i understand... is it correct?

No. The weak signal from the microphone modulates the DC voltage at pin 3.

The DC voltage at pin 3 is half the power supply voltage because the two resistors in the voltage divider have equal values and the input of the opamp has a very small current.

 

[whiz115]

No. The weak signal from the microphone modulates the DC voltage at pin 3.

one very last question....
i hope that someone can answer or else i'll stay with a big ?

this modulated signal how does it look like? i'm asking this because i feel that by doing that stuff with R2,R3 resistors we have already amplified our weak signal coming from the electet!

i know it's impossible to be as simple as that, because op-amps and transistors would be useless! if we could amplify so easily a AC signal.