Audio amplifier using only 1 op-amp [single supply]

In summary, the student is trying to amplify a microphone signal using different circuits, and is having trouble with gain. He is also trying to figure out how to filter out certain frequencies. He is using an LM386 amplifier which he plans to buy tomorrow.
  • #1
Bassalisk
947
2
As the thread suggests, I am trying to amplify the signal from a microphone.

Now, I have a circuit which uses 2 op amps with dual supply.

That circuit works pretty well.


I have to make now, a amplifier using only one op amp, single supply.


The sound itself isn't of much importance, I just need the signal, it can be distorted(a little),

because I am not sending that signal to a speaker, but to a LED driver, in bar mode.


I attached a circuit.

Can this be done with only 1 op amp, and if it can, can somebody suggest me a circuit?

Thank you.

p.s. I am using elecrtet microphone.
 

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  • #2
my browser is giving trouble can't see your sketch
anybody else getting 502 errors on IE?

anyhow,
check LM386 it's a versatile little audio amplifier
 
  • #3
Hmmm. I will buy it tomorrow. This may as well solve my problem!

It even works with single supply! Thank you mr. Jim!
 
  • #4
Not sure I get your question.

Why not just use any op amp with a resistor in the feedback and a resistor in the input? Gain will be -RF/Ri if the + terminal is grounded. If the negative output is a problem...put your input into the positive terminal...ground the former input resistor...and the same feedback resistor. Gain will be (1+ RF/Ri)

If you need to filter out high end frequencies...put a capacitor in parallel with the feedback resitor. If you want to get rid of lower frequencies...put a resistor in series with the input resistor?

Break frequencies happen at 1/(2*pi*R*C)?

The basics of op amps right? Am I missing something...probably!

I'm more than sure the LM386 will work great...but wouldn't pretty much any op amp work as long as it has the required power you need?
 
  • #5
psparky said:
Not sure I get your question.

Why not just use any op amp with a resistor in the feedback and a resistor in the input? Gain will be -RF/Ri if the + terminal is grounded. If the negative output is a problem...put your input into the positive terminal...ground the former input resistor...and the same feedback resistor. Gain will be (1+ RF/Ri)

The basics of op amps right? Am I missing something...probably!

I'm more than sure the LM386 will work great...but wouldn't pretty much any op amp work as long as it has the required power you need?

Problem was mainly because, my microphone was driving the op amp into negative saturation.

So I had to raise the voltage on the +ive lead. That solved the problem. Or so I thought. Now I had problem with gain. I put a 100 000 ratio resistors, but op-amps frequency characteristics knocked in, and I was pretty much nowhere. Then I thought, why not use again 2 op amps with single supply. I tried that, with different resistor ratios, and I was almost there, but I couldn't get the gain needed. I wasn't amplifying all frequencies equally enough(I think that was the problem). I did work on this like half an hour(spent 4h working on other parts of this project), was really tired, I will try again tomorrow(this with 2 op amps)

So I will probably go with this IC mr. Jim suggested. That looks like a winner, and I don't have to bust my head with 2 op amps.
 
  • #6
Wow...the LM86 costs a whopping 2 dollars! Not bad.

For fun...play with some capcitors in the feedback in paralell...and some capacitors in series to see if you can cut off low and high frequencies outlined to what I said above.

If you get it to work...you just designed a basic "equalizer". Put in a variable resistor in the feedback and you now have a volume control.
 
  • #7
Oh...I was just able to really zoom in on your drawing...you certainly did use to op amps as non inverting amps...cool.

I guess having an op amp powerful enough is your only issue. Might want to check the specs on the LM386 before you get it. Then again...for $2, no biggy.
 
  • #8
psparky said:
Wow...the LM86 costs a whopping 2 dollars! Not bad.

For fun...play with some capcitors in the feedback in paralell...and some capacitors in series to see if you can cut off low and high frequencies outlined to what I said above.

If you get it to work...you just designed a basic "equalizer". Put in a variable resistor in the feedback and you now have a volume control.

Yes I am enjoying this very much. And here at my store, LM386 is a dollar :P

Will try that!

This project was something my teaching assistant gave me, you know, for fun. Problem is, I don't have oscilloscope at home, nor dual supply, so I am limited to my lab at university.
 
  • #9
LM324 is a great little single supply opamp but not much current drive and not real fast.

It'll run from a 9v battery or wall-wart .

I bought a tube of them, lifetime supply, for just a few bucks..
4 amps in a 14 pin DIP!
 
  • #10
jim hardy said:
my browser is giving trouble can't see your sketch
anybody else getting 502 errors on IE?

anyhow,
check LM386 it's a versatile little audio amplifier

It's been bad the last few days, I couldn't get in for a few hours two days ago and this is the first time I can get in today. Yes, 50x error.
 

1. How does an audio amplifier using only 1 op-amp work?

An audio amplifier using only 1 op-amp is a simple circuit that uses an operational amplifier (op-amp) to increase the amplitude of an audio signal. The op-amp is configured as a non-inverting amplifier, where the input signal is connected to the non-inverting input and the output is fed back to the inverting input through a feedback resistor. This creates a closed loop with high gain, allowing the op-amp to amplify the input signal.

2. What are the advantages of using only 1 op-amp for an audio amplifier?

One of the main advantages of using only 1 op-amp for an audio amplifier is its simplicity. With just one op-amp and a few additional components, it is possible to create a functional audio amplifier. This makes it a cost-effective and space-saving option compared to multi-op-amp circuits. Additionally, using only 1 op-amp reduces the chances of noise and distortion in the output signal.

3. Can an audio amplifier using only 1 op-amp be used with a single supply voltage?

Yes, an audio amplifier using only 1 op-amp can be designed to work with a single supply voltage. It is important to choose an op-amp with a rail-to-rail output, which means it can output a signal that reaches the full range of the supply voltage. This allows for a wider dynamic range and louder output signal. Additionally, capacitors can be used to create a virtual ground, allowing the op-amp to work with a single supply voltage.

4. What are the limitations of using only 1 op-amp for an audio amplifier?

Using only 1 op-amp for an audio amplifier may not provide enough gain for some applications. Additionally, it may not be suitable for high power or high fidelity audio signals. The single supply voltage may also limit the output voltage swing of the amplifier. It is important to consider the specific requirements of the audio signal and choose an appropriate op-amp and circuit design for optimal performance.

5. Can an audio amplifier using only 1 op-amp be used for other applications besides audio amplification?

Yes, an audio amplifier using only 1 op-amp can be used for other applications besides audio amplification. The same circuit can be used for signal conditioning and amplification in various electronic systems, such as sensors, filters, and communication devices. However, the circuit may need to be modified to accommodate for different input and output signal requirements.

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