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LM1972 for mixer volume control

Jay Shoemaker
Intellectual 650 points
Other Parts Discussed in Thread: PGA4311, LM1972, PGA2311

Hello,

I'm building a "digitally controlled analog mixer" with some mic inputs and stereo linear inputs. I need each channel to have a volume slider. 

We considered the PGA4311, but a) it's expensive and b) it has some extra features we don't need. Our microphones are going to be differential, so we are putting an opamp (NE5523) on the input of the mics anyhow, so we have plenty of gain already. The PGA4311 has additional gain that we don't really need. 

So we are now considering the LM1972. Will this work for my needs? I know it has some attenuation, and it has a "mute" function, but will it work as expected as a "volume control" for each of the mics and inputs? Will we be able to create the curve you'd most likely associate with a volume slider on a mixer board where all the way up is on and all the way down is off? Or will there be an issue with the sliders not going from 0 to 100?

Hopefully my question is clear enough. Please feel free to ask me if you need clarification. Thank you for your time!

Jay

  • 0
    TI__Guru* 98965 points
    Hi Jay,

    Some details about the attenuation stepping are on LM1972 datasheet figure 16 and table 1.
    What kind of volume slider are you planning to implement? LM1972 is digitally controlled through 3-wire serial interface.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Intellectual 650 points
    Hello Ivan,

    We are creating a digitally controlled analog mixer. It will have a differential microphone preamp, and a line-level input. The microphone and the line-level inputs will both be digitally controlled with a 3-wire Serial Interface.

    On the microphone input, we are debating the LM1972 or the PGA4311. Because we are using differential inputs, we are using an op amp as the input for the microphone's differential signal pair. Because of that, we can boost the microphone at the opamp, and then attenuate with the LM1972. Or we can use the Op Amp with unity gain, and then use the PGA4311 with it's 32db boost. What are the pros and cons of each in this use case?

    On the line-level inputs, I'm pretty sure the LM1972 is going to work fine. We assume that the source player will have enough boost to send a normalized signal, then all we need to do is attenuate the signal with the LM1972. Does this sound like a resonable solution to you? I'm just trying to figure out what might make best sense.

    Thanks for your input.

    Jay
  • 0 in reply to Jay Shoemaker
    TI__Guru* 98965 points
    Hi Jay,

    PGA4311 has the advantage that is 4-channel. But if your system requires only two channels LM1972 looks like a better option.
    One thing that could be a disadvantage of LM1972 is that it states in the datasheet that a buffer at the output might be required for a good system operation while PGA4311 claims to be able to drive loads without buffering.
    If you don't need the four channels of PGA4311 you could take a look at PGA2311 which has the same functionality but this one is stereo.

    Best regards,
    -Ivan Salazar
    Texas Instruments