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As I said on the other site, an 8 ohm speaker needs hundreds of milliamps, but an opamp has a max output of only 20mA.
So use an LM386 power amp IC instead.
1K resistors for Rb,
a 1M resistor for R2,
a 1K resistor for R1,
a 10uF cap as already seen,
a .47uF cap for the coupling cap from the mic to the IC,
a LM741 IC and a 68uF cap out of the IC to the speaker....
1K resistors for Rb,
a 1M resistor for R2,
a 1K resistor for R1,
a 10uF cap as already seen,
a .47uF cap for the coupling cap from the mic to the IC,
a LM741 IC and a 68uF cap out of the IC to the speaker....
The component values don't really matter, it's a preamp, NOT a power amp, and can't be used to feed a loudspeaker. I would suggest feeding the output of that to a poweramp, like the LM386, if you want to make a complete amplifier.
However, asking for a gain of 1000 from a 741 is also rather hopeful?, no doubt audioguru will tell us the bandwidth you could expect at that gain? - it won't be much!.
A 741 opamp will have high distortion when driving an 8 ohm speaker with an output power more than only 1.6mW because its max output current is only 20mA. 250mW from a power amp IC into 8 ohms is a peak current of 250mA.
The 741's high frequency response will drop above only 200Hz when it has a gain of 1000.
The 68uF cap that feeds the speaker will reduce low frequencies below 400Hz.
So your "amplifier" doesn't have any power, doesn't have any high frequency response and doesn't have any low frequency response. No wonder it sounds terrible.
Not every piece of audio can be amplified with only one chip.
Basically, what you want to do is adjust the 1M resistor. then adjust the others until you get high quality sound. Ignore the volume. If you can hear the quality, then you are about half way there. Then add another amplifier that can handle higher voltage and current, so that no chip will heat up.
You can probably copy your design and chain them together (connect output of the 1st circuit to the input of the 2nd, etc), Now connect the output of the last circuit to the speaker or earphone. Then you will have at least a 2-stage amplifier.
I have worked with the 741 about a few years ago, and I stopped using it because I wanted to use more transistors. Also, some transistors amplify better at higher frequencies.
Don't use an old 741 opamp for an audio preamp. It runs into trouble at high output levels above only 9kHz when it has any amount of gain.
Use a TL071 audio opamp which is less expensive, has much lower distortion and noise and has a bandwidth to 100kHz. Inexpensive and very good TL072 dual and TL074 quad opamps are also available.
I wonder if he has a bias resistor for the electret microphone. It is not shown on his schematic.
Perhaps he wouldn't have ANY output if it were omitted.
You got this guy setup for a gain of 1000 that is a lot 3.5 mv and you got saturation then the LM 741 don't recuparetes fast either and might latch up the output cut the gain by some factor then listen to others help about power handling even an LM386 can handle an 8 ohm speaker try higher power amp capability. and if you intend to use a 9v battery forget it will work once and die and time to change battery again. there are 100 ohms speakers for intercomms quality is another question
I wonder if he has a bias resistor for the electret microphone. It is not shown on his schematic.
Perhaps he wouldn't have ANY output if it were omitted.
Hi, I finished an LM386 based amp this week and was wondering if there are any other IC's that I could try out in place of the LM386; a direct equivalent with the same pinout that I can drop right in the socket. I'm mostly curious to know if there is a chip that consumes less power so the batteries can last longer. Also, is the LM386 considered to be a power hog, or is it pretty efficient compared to similar chips?
I'd also like to know about LM386 equivalent chips that can produce more volume output as well. I will use the amp plugged into the wall outlet sometimes and wouldn't mind having a chip I can drop in for more volume when current consumption and battery life isn't a factor.
Lastly, can anyone tell me the most efficient power amp IC('s) they know of - regardless of pinout? Something that provides a reasonable amount of volume and will not drain batteries quickly. Any tips on limiting current drain when designing an amp circuit? I'd like to build a very energy efficient amplifier in the future.
Apologies for the barrage of questions. Any info on this at all is appreciated. Thanks.
Hi, I finished an LM386 based amp this week and was wondering if there are any other IC's that I could try out in place of the LM386; a direct equivalent with the same pinout that I can drop right in the socket. I'm mostly curious to know if there is a chip that consumes less power so the batteries can last longer. Also, is the LM386 considered to be a power hog, or is it pretty efficient compared to similar chips?
I'd also like to know about LM386 equivalent chips that can produce more volume output as well. I will use the amp plugged into the wall outlet sometimes and wouldn't mind having a chip I can drop in for more volume when current consumption and battery life isn't a factor.
Lastly, can anyone tell me the most efficient power amp IC('s) they know of - regardless of pinout? Something that provides a reasonable amount of volume and will not drain batteries quickly. Any tips on limiting current drain when designing an amp circuit? I'd like to build a very energy efficient amplifier in the future.
Unfortunately it's not as simple as that - power output is (mainly) dependent on the impedance of the speaker, and the power supply feeding the amplifier. The main contribution from the amplifer is that it will stand the voltage supplied to it, and be capable of supplying the current demanded by the load, both without getting too hot and destroying itself.
The LM386 is a decent little chip, but if you want longer battery life there are a number of amplifier chips specifically designed for such use, but they are usually lower output power, and higher distortion.
For good battery life and output power you need a high effeciency PWM amplifier chip, sometimes called a digital power amp. These waste very little power compared to class A, AB or B designs (they are called class D, the D stands for digital though). Search around for them, "class D low voltage amplifier" might find something suitable.
If you want longer battery life then just turn down the volume!
You could also use a bigger speaker that uses less power to sound as loud as a smaller speaker. Headphones use very low power.
With a 9V supply, an LM386 draws about 4.3mA without sound, and about 122mA at clipping into an 8 ohm speaker. A modern class-D amplifier would draw about 10mA without sound and about 85mA at the same lloudness as the LM386 is at when it is barely clipping.
The modern class-D amplifier is in a tiny case with many "surface-mount" little pins very close together.
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