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PGA2311 based volume control PCB components

Marko Frelih
Prodigy 60 points
Other Parts Discussed in Thread: PGA2311, DRV134, INA137, INA134

Dear Sirs and Madams!

I am building PGA2311 based preamp and since I am newbie, I just want to know, which components reside beside volume control IC in professional preamp. At the PGA2311's left and right output pins I've already add active bandpass filter with LME49710 (20 Hz - 20 kHz) with calculated gain 1 (RC values beside LME49710). What else is missing? I am sorry for kind of stupid question in advance. And, what kind of resistors and capacitors should I use with LME49710 for top audio performance?

Sincerely yours,

Marko

  • 0
    TI__Mastermind 27715 points

    Hello Marko,

    The passive components in your signal path should definitely be selected with care as they will have an significant effect on your system's performance. Thankfully, some resources exist to help you do this.

    My colleague John Caldwell wrote an excellent article showing how many common ceramic capacitors can introduce distortion, and to avoid this by using caps of dielectric type C0G or NP0:
    Signal Distortion from High-K Ceramic Capacitors

    Here are some documents on resistor selection for high-performance audio applications:
    Audio Noise Reduction Through the Use of Bulk Metal Foil Resistors
    Selecting Resistors for Preamp, Amplifier and Other High-end Audio Applications

    Depending on the characteristics of what's connected at the input and output of your preamp circuit, AC-coupling capacitors may be required as well.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps 

  • 0 in reply to Ian Williams
    Prodigy 60 points

    Thank you very much for guidelines, going to read them! But, I also cannot "decode" what are that DRV134/135 (Line Drivers) used for, i.e., will I need them for quality audio signal transport from preamp to power amp?

  • 0 in reply to Marko Frelih
    TI__Mastermind 27715 points

    Hello Marko,

    A line driver such as the DRV134 is only necessary if the power amp will connect to your preamp with differential (balanced) cables such as XLR or TRS. A DRV134 on each output channel would convert the single-ended PGA2311 output to differential and would easily drive the signal across the cable. A differential line receiver such as the INA134 or INA137 would be used on the other end to convert back to single-ended before the power amp.

    If the power amp will connect to your preamp using single-ended (unbalanced) cables such as RCA, then the line driver is unnecessary. This is also true if the power amp will be on the same PCB as the preamp.

    Best regards,

    Ian Williams