mc1458 op-amp audio amp

Discussion in 'The Projects Forum' started by Rednecklawrence, Nov 3, 2015.

  1. Rednecklawrence

    Thread Starter New Member

    Jul 15, 2015
    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?
  2. Roderick Young


    Feb 22, 2015
    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.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    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
  4. OBW0549

    Distinguished Member

    Mar 2, 2015
    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...
    Sinus23 and DickCappels like this.
  5. Rednecklawrence

    Thread Starter New Member

    Jul 15, 2015
    I was hoping to get away from the LM386's cause I don't have any... allright. thanks anyways!
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
    If you have a bunch of the MC1458 op amps, then you can connect them in parallel, get 250 mA out per 10 units.
  7. dl324

    AAC Fanatic!

    Mar 30, 2015
    You could put a current booster on the 1458's output.
    Sinus23 likes this.
  8. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    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.

    Sinus23 likes this.