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

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Discussion Overview

The discussion revolves around designing an audio amplifier using a single operational amplifier (op-amp) with a single supply, specifically for amplifying signals from a microphone. Participants explore various circuit configurations and components suitable for this application, including the LM386 and other op-amps.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes their existing circuit using two op-amps with dual supply and expresses the need to create a simpler circuit with a single op-amp.
  • Another participant suggests the LM386 as a versatile audio amplifier that works with a single supply.
  • Some participants discuss the basic principles of op-amp configurations, including feedback and gain calculations, indicating that many op-amps could potentially work for the application.
  • Concerns are raised about the microphone driving the op-amp into negative saturation, leading to adjustments in voltage and gain settings.
  • One participant mentions experimenting with capacitors in feedback to create an equalizer effect and control volume.
  • Another participant notes the LM324 as a single supply op-amp option, though it has limitations in current drive and speed.

Areas of Agreement / Disagreement

Participants generally agree that the LM386 is a suitable option for the project, but there are differing opinions on whether other op-amps could also work effectively. The discussion remains unresolved regarding the optimal configuration and components for the amplifier.

Contextual Notes

Participants express limitations in their setups, such as not having access to an oscilloscope or dual supply, which may affect their experimentation and results.

Who May Find This Useful

Individuals interested in audio amplification, circuit design, and those working with operational amplifiers in single supply configurations may find this discussion beneficial.

Bassalisk
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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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Engineering news on Phys.org
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
 
Hmmm. I will buy it tomorrow. This may as well solve my problem!

It even works with single supply! Thank you mr. Jim!
 
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?
 
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.
 
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.
 
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.
 
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.
 
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.
 

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