1
\$\begingroup\$

At the output of an LM741 opAmp I have 16Vpp sine wave @ no load. I want to use this sine wave on an 8 ohms load with 1.5W power . Therefore I need 3.5 Vrms and 0.43 Arms on the load. Now, if I directly connect the load to the output of the opAmp, the voltage on the load drops to 0 immediately, and I assume this results from the fact that max current output of opAmp is around 20mA so it is not enough obviously.

Also I want to be able to adjust the power on the speaker, i.e the amplitude of the incoming sine wave.

So, what is the best method to drive that load with adjustable levels of output voltage? I would appreciate if anyone supplies an answer not involving buy this regulator or buy this converter etc. (***)Rather I prefer things like building a transistor amplifier circuit etc. Anyway, I am also open to other advices.

*** : actually, I have to design all these steps for a project. That's why I ask the fundamental methods. I know how silly it seems not using a commercial IC. By the way, the output of the 741 is the direct source of the sine wave. It is a sine wave generator(wien bridge oscillator) actually. I wonder can I do the amplification part seperately from that 741 oscillator circuit.

p.s : don't think matters but the load is a speaker which will be driven at 1kHz.

\$\endgroup\$
5
  • \$\begingroup\$ p.s : don't think matters but the load is a speaker. It does matter, speakers are somewhat inductive and don't have a constant resistance over frequency like a resistor does. \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 28, 2019 at 8:53
  • \$\begingroup\$ @Bimpelrekkie it will operate at a constant frequency. In that case, can I account its resistance as fixed? \$\endgroup\$
    – muyustan
    Commented Nov 28, 2019 at 8:57
  • 2
    \$\begingroup\$ I still would not approach it like that, in theory a speaker + amplifier could be such that the combination would oscillate. That can be at a frequency you don't use but the amplifier doesn't care about that, it will still oscillate. But you're over asking, what you need is an audio power amplifier so just buy a module for that. There is no need to build a circuit around the 741 opamp you have. If you insist on using a 741, find an existing design for a PA based on a 741. They do exist. But buying a module is much much simpler. \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 28, 2019 at 9:01
  • \$\begingroup\$ @Bimpelrekkie actually, I have to design all these steps for a project. Thats why I ask the fundamental methods. I know it seems silly not using a commercial IC. By the way, the output of the 741 is the direct source of the sine wave. It is a sine wave generator(wien bridge oscillator) actually. I wonder can I do the amplification part seperately from that 741 oscillator circuit. \$\endgroup\$
    – muyustan
    Commented Nov 28, 2019 at 9:06
  • 1
    \$\begingroup\$ I suggest that you search for wien bridge oscillator designs and audio amplifiers to see what is commonly used. I think you can combine the oscillator and amplifier. I would build a "power opamp" based on the 741 and some transistors. Here's an example of that: electronicecircuits.com/electronic-circuits/… \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 28, 2019 at 9:14

1 Answer 1

Reset to default
1
\$\begingroup\$

You are looking for an audio amplifier, there are tons of these within your requirements, just need a little search.

Just make sure to adjust your signal levels to what you need.

\$\endgroup\$
3
  • \$\begingroup\$ The link you have provided is broken, but I get the point. Thanks. \$\endgroup\$
    – muyustan
    Commented Nov 28, 2019 at 8:58
  • \$\begingroup\$ @muyustan i fixed it \$\endgroup\$
    – Damien
    Commented Nov 28, 2019 at 8:59
  • \$\begingroup\$ your answer is actually the solution to the case, however I am more of looking for a solution not involving a direct purpose IC. Anyway thanks. \$\endgroup\$
    – muyustan
    Commented Nov 28, 2019 at 9:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.