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 ?
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.
Audio Applications Engineering Manager
Dallas, TX USA
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,
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.
Thank you very much for your explanations and your support.
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