OPA1642: What would suit my phono stage circuit in my amplifier

Hi Sam,

I think in this case, you could use almost any amplifier. In this design, Q101 and Q103 create a low-noise FET front end on the amplifier, so the choice of the op amp shouldn't change loading on the source all that much. The noise performance of these FETs will also dominate the noise behavior of the overall circuit, so chosing the absolute lowest-noise op amp may not be necessary.

OPA1642, or OPA1688 are good choices for a FET or CMOS op amp in this application. You could also consider OPA1652 as another option here.

If you'd prefer to use a bipolar input op amp, I'd suggest OPA1662 or OPA1602. OPA1612 could certainly be used here, but it may be overkill in this application since noise performance of this circuit is likely to be dominated by the noise from the FET input stage.

Since all of these options are only available in surface-mount packages, you might want to look at our DIP adapter EVM, which can adapt many common SMT op amp packages to a DIP socket: www.ti.com/.../dip-adapter-evm

Hi Kai, that is actually low input noise. Some of those Technics parts are quite low in noise.

Regards
Sam

Sam, Kai,

I realize looking back at my answer above that I worded it a little poorly.

In this case, because of the way the circuit is designed, the voltage and current noise of the op amp itself effectively appear inside the feedback loop, and so should be corrected for by the op amp's loop gain itself (at least until the op amp runs out of loop gain at high frequency). In this sense, the JFET noise will be the dominant factor in the overall noise performance of the circuit, and choosing an ultra-low-noise op amp may not be strictly necessary.