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Multiply op amp to divide the noise

HOFF Remy
Prodigy 50 points
Other Parts Discussed in Thread: OPA627

Hi all,

I ever work in an accurate op amp topology for an audio preamp.

I  heard some works about a topology wich consist of multiply the number of op amp (in parallel, with a 10R out to put the out together).

Two op amp should decrease the noise by 3dB, 4 op amp by 6db, etc.

Had you experiment this or have a opinion ?

 

  • 0
    TI__Guru**** 189401 points

    Hoff,

    Just buy the OPA627 and be done with it. It is the golden standard in Audio op amps. Heck, I even bet my good friend JD would agree with that statement! :)

    I don't see how paralleling op amps could lower noise unless you put one op amp inside the feedback loop of another op amp which makes my head hurt.

    -d2

  • 0 in reply to Don Dapkus
    TI__Expert 3840 points

    Hi Hoff,

    If each of the op amp outputs are summed with equivalent resistors (as ballast resistors isolating each op amp output from the other), then it should be possible to reduce the noise. Note each op amp has its own feedback path and gain-setting resistors with the ballast resistors outside of the feedback loop. While each op amp noise source is not correlated, the noise will combine at the summed output in an RMS fashion with the key being that each op amp's noise voltage will be reduced by the voltage divider created by the ballast resistors; divide by 2 or 4 depending upon number of op amps, 2 and 4 respectively.

    I would concur with Don that the OPA627 is a very well known standard op amp and his advice of just buying one is definitely the easy way to go. If that particular device's noise spec is not low enough TI surely has other lower noise ICs to choose from.

    Best of Luck,

    JD

  • 0 in reply to John De Celles
    TI__Expert 3840 points

    Hi Hoff,

    Attached is a quick write-up, exemplifying how you could reduce overall output noise by paralleling op amps. Paralleling 2 op amps to reduce noise by -3dB and paralleling 4 op amps to reduce noise by -6dB.

    Best Regards,

    JD1033.OpAmp_Vonoise_Reduction_121912.pdf

  • 0 in reply to John De Celles
    Prodigy 50 points

    Hi John,

    Thank you very much for your explanations and your support.

  • 0 in reply to John De Celles
    Expert 2056 points

    I get "403 - Forbidden: Access is denied."