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OPA1656: Impedance of the supply rail - flat across the bandwidth

Gary Follett
Prodigy 10 points
Part Number: OPA1656
Other Parts Discussed in Thread: LM4562,

Hello,

I am designing a phono pre-amp and found application report SNAA046A–July 2007–Revised May 2013.  Can I please ask two questions.

1) Can I replace the LME49710 / LM4562 referred to in the report with the OPA1656 without changing any of the values in the circuit design in the report?

2) The report states that "power supply rails must present a low and more importantly flat impedance across the audio bandwidth to preserve the audible spectral balance and overall integrity of the input signal" and "impedance of the supply rails is addressed in this application."  Can you please explain the operation of U4 and U5 in the "Figure 2. Passive EQ RIAA Phono Pre-Amplifier Topology" which presumably are addressing the impedance of the supply rails?

kind regards

Gary

  • 0
    TI__Expert 6400 points

    Hi Gary,

    Thank you for your questions.

    I understand the author of the application report consider the phono-pre amp as very noise sensitive application, so the ripple filter U4/U5 was addressed.

    However, the current design is not good to OPA1656 due to the phase margin.
    I will prepare several design to achieve compatible performance to the application report.

    Thank you for your patience.

    Best regards,
    Iwata Etsuji