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LME49860: Replacing NJM5532 with LME49860

user5217667
Prodigy 20 points
Part Number: LME49860

Hi there,

I  intend to change 2 NJM5532 opamps with LME49860 in a Yamaha CX-50 preamp because only this opamp is able to  withstand  + -21V supply voltage (and obviously due to much better sonic characteristics of the latter).

However: the original design seems to be a bit upside down and  I am not sure if  a direct replacement,  without any modification of the original circuit, is possible  without damaging these IC's.

I also believe that some of the decoupling capacitors can be taken out (?) but I am not sure how this would influence the original  circuit. Finally, I am afraid that the circuit might start to oscillate after the replacement,  as it was specifically designed for NJM5532 and may become more noisy for the same reason.

I know these questions are a bit challenging,  but it would be interesting to know expert's opinion about this issue. 

Thank you and best regards,

Zeljko

  • 0
    TI__Guru** 102045 points
    Hi Zeljko,

    Welcome to e2e.
    LME49860 is specified for a capacitive load of 100pF, if the load is greater than this it must be isolated using a series resistor at the output. If you worry about instability you could add this resistor at the output.
    These devices are pin to pin compatible so it could fit as a replacement.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Prodigy 20 points

    Hi Ivan,

    Thank you very much for the advice.

    Replacing this op-amp was an easy task, and the results were impressive indeed, much better sound picture and transparency and  much clearer voices (I listen mostly to the classical music).

    One might say that there is too much subjectivity in my verdict,  but I would say that all this was worthwhile.

    However, now there is a newly emerging problem - radio interference, due to some of the connecting cables being too long and acting like antenna. How can I kill these parasitic frequencies  without influencing otherwise excellent performance of this chip and frequency range?

    It is barely notable but when everything goes quiet some crackling sound (although barely audible) appears, and it looks like radio interference (although, I am not surprised with this phenomenon because there are many transistors and diodes in the muting circuit which seem to behave like radio receiver).

    Would it be of help if I add some "pF" value ceramic capacitor  between the input and the ground after the buffer circuit? I have observed that similar solution was applied in my old Denon  CD player DCD 3300 . (I do not use tone controls, I rather by-pass them by means of a switch).

    Thank you again and best regards,

    Zeljko