mc1458 op-amp audio amp

Thread Starter

Rednecklawrence

Joined Jul 15, 2015
18
Hey, I was wondering if it would be possible to use a mc1458 dual op-amp to amplify a signal from an mp3 player, computer, etc, to drive two 8ohm 2watt speakers. Is it possible?
 

Roderick Young

Joined Feb 22, 2015
408
The LM1458 is not made for driving low impedance loads like speakers. Usually, your load is like 1k or higher in resistance. That said, it could sort of work. What you would do is put a capacitor of 10 - 100 uF between the output and the speakers. You would also put capacitors of perhaps 1 uF between the inputs and the MP3 player. You would configure the op-amp for the gain that you want, remembering that the ic only has that limited drive capability. The speakers might be soft.

A better choice might be to use two LM386's, or some dual audio amplifier chip designed especially for that purpose.
 

MikeML

Joined Oct 2, 2009
5,444
AFAICR, the peak current out of a '58 is like +-25mA, which would be like 18mArms. Pout = I^2*R so you could expect 0.018^2*8 = 2.5mW without distortion... That's not even enough to drive 8Ω headphones...ν
 

OBW0549

Joined Mar 2, 2015
2,984
Hey, I was wondering if it would be possible to use a mc1458 dual op-amp to amplify a signal from an mp3 player, computer, etc, to drive two 8ohm 2watt speakers. Is it possible?
An MC1458 has a peak output current of about ±25 milliamps (0.025 amps), which will give you an ac output current of 17.7 mA rms. That amount of current into an 8Ω speaker will give you 0.0025 watts of power. If you listen very, very carefully in a very quiet room you probably would be able to hear it...
 

AnalogKid

Joined Aug 1, 2013
8,103
Hey, I was wondering if it would be possible to use a mc1458 dual op-amp to amplify a signal from an mp3 player, computer, etc, to drive two 8ohm 2watt speakers. Is it possible?
No. Calculate the peak current and voltage needed to pump 2 W RMS into 8 ohms, and you'll see that a 1458 can't make the current. You can add a booster circuit to its output stage. Search for opamp booster circuit.

ak
 
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