Making an Audio Amplifier with a TL082

Thread Starter

Fredje

Joined Jun 1, 2022
19
Hello everyone,
For our schoolproject we need to have a loudspeaker. I wanted to build an audio amplifier circuit but the problem is we can't buy any related IC's nor an amplifier specific for audio.

So I tried making a simple non inverting amplifier with a TL082 but I had the feeling it didn't really work.

Is it possible to use a TL082 for amplification of audio? how should the circuit look alike?

Kind regards,
 

Ian0

Joined Aug 7, 2020
9,668
As this is homework help, we need to see your best effort so far. The clue I can give you is that you need something on the output to increase the current.
 

Thread Starter

Fredje

Joined Jun 1, 2022
19
What I already tried is building a NI Amplifier and I used a 47k and a 27k resistor to have +/- x2 amplification. I checked on the oscilloscope and the circuit was working as it should. But once I tried connecting the loudspeaker to it. I got a signal that looked like PWM.
1671698696728.png
Should I add a capacitor in parallel with the load on the output to increase the current?
 

Ian0

Joined Aug 7, 2020
9,668
Look at the TL082 datasheet, and you will find graphs of output current, which show that the maximum available is about 25mA.
How much current do you need for the loudspeaker?
 

Thread Starter

Fredje

Joined Jun 1, 2022
19
I am using the ABS-210-RC as loudspeaker. In the datasheet the current isn't specified. All I get is:
https://www.farnell.com/datasheets/2869760.pdf

  • Rated Impedance : 8Ω ±15%
  • Rated Power : 1W to 1.5W
  • Rated Resonant Frequency : 350Hz ±20%
  • Rated Frequency Range : fo to 20,000 Hz
  • Rated Sound Output Level, 10cm : 94dB ±3
  • Operating Temperature Range : -10°C to +40°C
  • Storage Temperature Range : -20°C to +60°C
  • Weight : 13.2g ±5%

I don't think the loudspeaker needs that much current. But are you implying that the TL082 can't give enough current to drive the loudspeaker?

1671701404532.png
 

MrChips

Joined Oct 2, 2009
30,712
I am using the ABS-210-RC as loudspeaker. In the datasheet the current isn't specified. All I get is:
https://www.farnell.com/datasheets/2869760.pdf

  • Rated Impedance : 8Ω ±15%
  • Rated Power : 1W to 1.5W
  • Rated Resonant Frequency : 350Hz ±20%
  • Rated Frequency Range : fo to 20,000 Hz
  • Rated Sound Output Level, 10cm : 94dB ±3
  • Operating Temperature Range : -10°C to +40°C
  • Storage Temperature Range : -20°C to +60°C
  • Weight : 13.2g ±5%

I don't think the loudspeaker needs that much current. But are you implying that the TL082 can't give enough current to drive the loudspeaker?

View attachment 283615
Correct.
You can calculate the required current by using the power equation,
Power W = I x I x R

Also the transducer is only a part of the loudspeaker. You need an enclosure for the transducer.
 

Thread Starter

Fredje

Joined Jun 1, 2022
19
Also the transducer is only a part of the loudspeaker. You need an enclosure for the transducer.
Okay, so when I calculate the current needed for the loudspeaker I need a current between 350 and 430 mA. So it is not possible to use the TL082, because it can't deliver enough current to drive the loudspeaker? (or I need to put 'something' after the circuit to deliver more current)

Also, what do you mean with enclosure for the transducer?
Thanks for your help!
 

Ian0

Joined Aug 7, 2020
9,668
Okay, so when I calculate the current needed for the loudspeaker I need a current between 350 and 430 mA. So it is not possible to use the TL082, because it can't deliver enough current to drive the loudspeaker? (or I need to put 'something' after the circuit to deliver more current)

Also, what do you mean with enclosure for the transducer?
Thanks for your help!
Here’s some reading for you
https://www.renesas.com/us/en/document/apn/r13an0008-boosting-op-amp-output-current

If you don’t put the speaker in a box, then you have two audio signals from it, one from the front and one from the back, and they are of opposite polarity. What will happen?
 

MrChips

Joined Oct 2, 2009
30,712
Okay, so when I calculate the current needed for the loudspeaker I need a current between 350 and 430 mA. So it is not possible to use the TL082, because it can't deliver enough current to drive the loudspeaker? (or I need to put 'something' after the circuit to deliver more current)

Also, what do you mean with enclosure for the transducer?
Thanks for your help!
It means a box to hold the transducer (loudspeaker).
The transducer produces a front wave and a back wave.
The back wave is out of phase with the front wave and the two will cancel.

The basic enclosure is the infinite speaker baffle board. Its purpose is to prevent the back wave from reaching the listener.
 

dl324

Joined Mar 30, 2015
16,845
I need a current between 350 and 430 mA. So it is not possible to use the TL082, because it can't deliver enough current to drive the loudspeaker? (or I need to put 'something' after the circuit to deliver more current)
You can put a class AB amplifier on the output of the opamp.
 

Audioguru again

Joined Oct 21, 2019
6,673
I looked in Google for "opamp in audio power amplifier circuit" and found the first one that does not work because it uses a 54 years old 741 opamp that does not work in the 6V powered circuit.
Your TL082 opamp can be used in that circuit to drive the two little transistors if it has a 10V or 12V supply.

Your tiny speaker produces no low frequencies.
 
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