Good morning,
My name is Cristian, I have been reading the Forum for 2 months (approximately). I'm interested in the world of audio, in fact, reading the forum and its recommendations, I already built the first circuit with an OPAMP NE5532.
Now, I have a problem, I need a maximum output of 3.5V (peak to peak, 3Vp-p would be acceptable too), since the ADC input of the microcontroller I am using works with that maximum voltage. I already managed to do it with a simple voltage divider on the output (as the attached image shows). However, I would like an alternative, an OPAMP that can be fed with + -1.75 or + 3.5V at 0V, to be able to feed my complete circuit using only a 3.6V battery. Is there an OPAMP with those characteristics?
The input is an electret microphone.
I know that the LM5532 can be powered with + -1.75V, but the recommended minimum is + -5V.
I hope you can help me, I would be very grateful.
My name is Cristian, I have been reading the Forum for 2 months (approximately). I'm interested in the world of audio, in fact, reading the forum and its recommendations, I already built the first circuit with an OPAMP NE5532.
Now, I have a problem, I need a maximum output of 3.5V (peak to peak, 3Vp-p would be acceptable too), since the ADC input of the microcontroller I am using works with that maximum voltage. I already managed to do it with a simple voltage divider on the output (as the attached image shows). However, I would like an alternative, an OPAMP that can be fed with + -1.75 or + 3.5V at 0V, to be able to feed my complete circuit using only a 3.6V battery. Is there an OPAMP with those characteristics?
The input is an electret microphone.
I know that the LM5532 can be powered with + -1.75V, but the recommended minimum is + -5V.
I hope you can help me, I would be very grateful.
Attachments
LTC6228 has low noise and distortion and sufficient BW
LTC6229 Datasheet and Product Info | Analog Devices
LTC6229 Datasheet and Product Info | Analog Devices
Wouldn't it be better to reduce the gain? Change R12 to the appropriate value. Lowering the supply voltage will only cause hard clipping of the output signal.
I would have gone for 2 stages with 15x gain and 5 times gain but get rid of output potential divider.
You might get instability with the 200k.
Thank you all for your answers, I will look at the technical sheet and simulate each of the OPAMPs that you suggested to me. 😀
Yesterday reading the NE5532 datasheet again, I realized that at high frequencies (20k Hz approx) the gain is drastically reduced, I had only simulated at low frequencies. So I separated the amplification in 2 stages of 15x. By simulating the new circuit, I obtained an output of 3Vp-p over the entire frequency range. Thanks to both.
Yesterday reading the NE5532 datasheet again, I realized that at high frequencies (20k Hz approx) the gain is drastically reduced, I had only simulated at low frequencies. So I separated the amplification in 2 stages of 15x. By simulating the new circuit, I obtained an output of 3Vp-p over the entire frequency range. Thanks to both.
Now I understood your question. The problem is that the OPAMP input signal is 30 mV when speaking at a distance of 30 centimeters or more from the electret microphone. But if you hit the microphone or talk too close, there are peaks of 130mV, so amplifying that voltage could burn out my ADC input. I made the voltage divider to protect my ADC input.
The 1/4" electret has a Resistor to +3.6V, being 2.2k probably. With this resistor it outputs 5mVeff at 1Pa = 94dB.
If you want to measure 114dB the output will be 150mVpp. So it makes sense to amplify only 20 times for 3Vpp.
R11 can be dropped completely, only adding to the noise. R12 is 20*2.2k = 44k use 47k, a small 33p across it makes the preamp more stable.
No need to attenuate the output.
Ground is the negative rail, because the mike is connected there.
R9 and R10 should be only 15k (for 3V) and go to a 3.3u capacitor to ground and the +in opamp (virtual gnd at +1.5V).
Put a 100 ohm resistor (stability) in series with the output cap and a 100k to gnd behind it.
Low noise Mini Electret Microphone PreAmplifier - Electronics-Lab
https://www.mouser.in/datasheet/2/670/cma_4544pf_w-1776632.pdf
If you want to measure 114dB the output will be 150mVpp. So it makes sense to amplify only 20 times for 3Vpp.
R11 can be dropped completely, only adding to the noise. R12 is 20*2.2k = 44k use 47k, a small 33p across it makes the preamp more stable.
No need to attenuate the output.
Ground is the negative rail, because the mike is connected there.
R9 and R10 should be only 15k (for 3V) and go to a 3.3u capacitor to ground and the +in opamp (virtual gnd at +1.5V).
Put a 100 ohm resistor (stability) in series with the output cap and a 100k to gnd behind it.
Low noise Mini Electret Microphone PreAmplifier - Electronics-Lab
https://www.mouser.in/datasheet/2/670/cma_4544pf_w-1776632.pdf
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