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LME49724 is a balanced audio op amp, correct?

Eric Koester
Prodigy 85 points
Other Parts Discussed in Thread: LME49724, INA163

Hi,

I want to know if the LME49724 is a balanced op amp similar to the Burr Brown INA163 and the THAT1570?

With the INA163 and THAT1570, the input impedance is said to be set with resistors that are parallel to the + and - inputs of the op amp, rather than with a series resistors connected to the + and - input pins.  You'll see this configuration in the data sheets for both referenced parts.  You'll note that there are NO series resistors connected to the inputs of these chips.

Bottom line:  Can I apply this same input configuration to the LME49724 for the application of a balanced microphone pre-amp?

Thanks,
Eric 

  • 0
    TI__Expert 3840 points

    Hi Eric,

    The LME49724 is a fully differential op amp; ie differential signal in/differential signal out with external gain-setting resistors as shown in Figure 1 of the datasheet. It is not the same as the INA163 which is an instrumentation amplifier nor is it the same as the THAT1570, as you have noted that the gain setting resistors are topologically different.

    You could probably apply the LME49724 as a balanced mic pre-amp presuming that there isn't loading on the mic pre, but not with the same topology as the other noted amplifiers due to the gain setting resistors.

    Best Regards,

    JD

     

     

  • 0 in reply to John De Celles
    Prodigy 85 points

    Thanks for the definitive response John.

    I'll be honest.  I was not able to tell from the datasheets of the 3 parts that they were different typologies inside.  Each data sheet says it's a differential input audio amplifier, so I concluded they were all the same and could be implemented in the same way.

    For my future reference, are there any clues in the LME49724 datasheet that would tip off a designer that these parts are different from other differential audio amplifier op amps and need to be connected differently?  If not, could some clues be added to the next revision of the data sheet?

    Thanks for your information,
    Eric 

  • 0 in reply to Eric Koester
    TI__Expert 3840 points

    Hi Eric,

    I guess with the similar title descriptions and promotional info the parts could sound like they are the same. The subtle differences can be gleemed from the connections shown in the application circuits and block diagrams.

    The INA163 is an instrumentation amplifier with 3 independent amplifiers internal to the IC with a single-ended output as shown by the block diagram on the first page of the datasheet. It is differential input but single-ended output with internal gain-setting resistors, except for RG. This type of amplifier is great for high gain and high common mode rejection as used in mic preamps.

    The THAT1570 is a diff-in/diff-out part with two pin connections, RG1 & RG2, which allow for gain control as with the INA163. Feedback resistors are external and connect to the RG gain connection.

    The LME49724 is a diff-in/diff-out IC, but the gain configuration is as shown in Figure 1 of the datasheet. The key difference of this part compared to the others would be the input impedance due to the gain-setting resistors, which if too low could load down the input source.

    Best Regards,

    JD

     

  • 0 in reply to John De Celles
    Intellectual 415 points

    "Can I apply this same input configuration to the LME49724 for the application of a balanced microphone pre-amp?"

    Eric - You wouldn't want to use the LME49724 as a microphone preamp. Among the many reasons are that the required input resistors will increase the overall source impedance and thus increase noise. The INA163 or THAT1570/THAT1583 current feedback topologies with their low voltage noise are better suited.