BA4560 output volume pointers ?

Discussion in 'General Electronics Chat' started by Slider2732, May 20, 2009.

  1. Slider2732

    Thread Starter Member

    May 6, 2009
    17
    0
    The basis of my question is that i'm not getting enough volume from a BA4560 op-amp. It's running from the clicks of a 555's output and out to an 8ohm .5W speaker.

    Several audio circuits i've built use the warm sounding BA4558 (without the '-1' as I believe that signifies later ones, where the internal structure was changed and they sound a little gritty). In the past i've used this chip from salvaged boards many times and run the output to headphones. One circuit for 8-bit sound sample playback used a 386 as audio amplifier and that was nice and loud, from an 8ohm .25W speaker. Unfortunately I have no more 386's, but did have a Rohm BA4560 for this project.
    The project is a metronome. My wife happily uses it for her piano playing but said she'd like a bit more volume.
    Following a 741's amplification circuit here: http://talkingelectronics.com/projects/OP-AMP/OP-AMP-1.html near the bottom of the page, I altered the BA4560 stage last night to incorporate the voltage divider and gain. The result was a volume exactly the same ! The components however did work, as tweaking values etc resulted in different tones from the speaker, or less volume.

    My deduction from these trials, is that the BA4560 is outputting at full volume already, from the tiny 555 click sound ?
     
  2. Slider2732

    Thread Starter Member

    May 6, 2009
    17
    0
    Forgot to mention that power is 6V.

    I just tried a TDA1517 6W power amp in the circuit, following the output of the BA4560 and using that as input. The output is slightly less (using 1000uF cap as in the datasheet example circuit), but the tone much more rounded. I'll try the 1517 on its own.
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Don't you believe the spec's in the datasheets?

    An opamp is designed to drive a load that is 2000 ohms and higher because its max output current is very low. An 8 ohm speaker is like a dead short to the output of an opamp.

    A power amplifier is designed to drive a low impedance speaker because its output current is much higher than an opamp.

    An LM386 has an output power of only 0.2W at clipping into an 8 ohm speaker with a 6V supply.

    An opamp will have an output power of only 0.004W at clipping into an 8 ohm speaker with a 6V supply, if you can fiond an opamp that works with a supply as low as 6V.

    A TDA1517 has two outputs that produce 4.5W each at clipping into 4 ohm speakers with a 14.4V supply. The power is 2.7W each into 8 ohm speakers. If the supply is only 6V then the output power into 8 ohm speakers is very low, maybe only 0.2W.

    The TDA1517 is not a dual opamp. It has its inputs already biased and has negative feedback. It has a voltage gain of 10 times.
     
  4. Slider2732

    Thread Starter Member

    May 6, 2009
    17
    0
    Most of the differences with this project have been in the output stage. My usual form of amplifying is into 32ohm earphones, something none too difficult to achieve. Usual choice has been the BA4558 and these have been found to work well at 6V for various purposes.
    The TDA1517 was found on an old PC modem card and, while the specs do call for a higher voltage for general use, these are functional down to 6V, with much less power being output of course.
    No problems with op-amp and power amp differences, my view was that while the 4560 gave a reasonable volume, a real amp would be preferable for the 0.5W speaker.

    Thanks for the figures :)
     
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