1

for the LM4952 chip (class AB amplifier), I wanted to add an NE5532 OA in voltage follower configuration at its input. That to take care of whatever input source will be plugged into it. Is it a good idea or just a waste of money?enter image description here

Status Re
  • 121
  • 6
  • 2
    What was your reason for wanting to add this part? Input sources, taking care of? Be more specific. – Andy aka Feb 16 '22 at 18:04
  • 1
    So I will always have a low impedance source at the end of it feeding the LM4952. Not having to warry if the audio input is an headphone output or a line out or bluetooth signal or something else – Status Re Feb 16 '22 at 18:28
  • 1
    The circuit doesn't show a voltage follower. At least, not for the voltage you want it to follow. –  Feb 16 '22 at 19:09

2 Answers2

2

I think it wise to put a buffer stage before the LM4952 because its input resistance varies with its gain, which is kind of lame.

But your circuit has some errors. You want your input coming into the non-inverting input, AC-coupled to +6V. Something like this will get you closer:

enter image description here

td127
  • 2,932
  • 6
  • 13
1

You need to make sure that the NE5532 is configured to have its audio input at around 6 volts (50% of the power rail voltages) because it isn't able to deal with input voltages that are close to its negative rail (0 volts in your circuit).

The knock-on effect of this is that you will then need to arrange for the correct DC voltage level to be superimposed on the amplified signal from the op-amp to suit your power-amp. This involves adding a series capacitor and possibly a biasing network to provide the right signal offset for the power amp. It may be simpler if the power amp is expecting an input voltage that swings around the 0 volts rail of course.

Or, you add a negative rail generator for the NE5532

Andy aka
  • 434,556
  • 28
  • 351
  • 777
  • Isn’t the LM4952 doing the same? I.e. biasing the input to around half supply? – Status Re Feb 22 '22 at 09:24
  • 1
    The inputs of the LM4952 cannot force the op-amp output to be correct @StatusRe – Andy aka Feb 22 '22 at 09:26
  • I mean, that if I bias the buffer (ne5532), I don’t need to do what you described here: “this involves adding….. – Status Re Feb 22 '22 at 09:28
  • 1
    Have you read the data sheet for the device? – Andy aka Feb 22 '22 at 09:38
  • I have. About the bypass pin 9 . Do i need to feed in my half supply? On another project with lm 4880 ( different chip same architecture) in order to use it with dual supply i have taken the bypass capacitor out and connected the bypass pin direct to ground – Status Re Feb 22 '22 at 09:46
  • 1
    I have no idea what other project you are talking about. Regards pin 9; do what the data sheet recommends and try looking at page 1 to see how they couple the inputs. I'm surprised you missed it; it was that clear and on the first page. Maybe you didn't *read* the data sheet but just glossed-over it? – Andy aka Feb 22 '22 at 09:48
  • 1
    Yes the input capacitor, i didn’t realize I didn’t add them at its input pins. Thanks – Status Re Feb 22 '22 at 10:05
  • If you are done with this Q and A you should formally accept one of the answers or raise a query in the form of a comment @StatusRe – Andy aka Feb 08 '23 at 12:02