# Utilizing a signal in the needed form to drive a load

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.

• 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. Nov 28, 2019 at 8:53
• @Bimpelrekkie it will operate at a constant frequency. In that case, can I account its resistance as fixed? Nov 28, 2019 at 8:57
• 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. Nov 28, 2019 at 9:01
• @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. Nov 28, 2019 at 9:06
• 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/… Nov 28, 2019 at 9:14