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Magic number in recommended RIAA phono preamp design procedure

Eugene Zagidullin
Prodigy 10 points
Other Parts Discussed in Thread: LM833

I refer to AN-346 "High-Performance Audio Applications of the LM833". The overall design procedure is quite clear for me. I only don't catch what magic number 8.058 means (page 5). I'm trying to adapt this design procedure to some kind of gain limited (about 100) differential amplifier instead of op amp. Even with open loop gain taken into consideration while computing feedback divider I can get recommended 19.3dB attenuation at 1kHz. Maybe this number is a clue?

  • 0
    TI__Guru*** 147446 points
    Eugene,

    The number isn't obvious to me. Perhaps is came about after much trial and error.
    I do not see much need for phonograph pre-amplifiers these days. Why not just use the LM833 circuit in the application note?
    What advantage do you expect from the fixed gain amplifier?