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CD4066B: CD4066 Audible Pop when Switching

Luke Galea
Intellectual 340 points
Part Number: CD4066B
Other Parts Discussed in Thread: TS5A22364

I am using the CD4066 to choose one instrument (GUITAR IN Pin 1 / SITAR IN Pin 3) and output the selected one to a common output PEDAL IN (Pin 2). The appropriate LED would also light when selecting either input.

I am currently testing the circuit shown in the schematic below with the addition of 2.2MOhm resistors at GUITAR IN, SITAR IN and PEDAL IN. The circuit works fine, however I am getting a very audible Pop when switching the input. Does anyone know what can be done to reduce this pop? 

  • 0
    TI__Genius 10974 points

    Hi Luke,

    The "pop" noise you are hearing occurs when there is charge previously built up on the selected channel that has not been able to be discharged.  Thus, this charge gets discharged through the speaker when switched causing an audible popping sound.

    To help reduce this issue, you need a way to make sure there is a discharge path (such as implementing an external shunt resistor) attached to the unselected inputs so they will not have any built up charge when switched to.

    In addition, we have switches in our portfolio that have built-in pop/click noise reduction that handles this for you. Please take a look at the TS5A22364 as an example and possible solution to use instead of the CD4066.

    Thanks!

    Bryan

  • 0 in reply to Bryan Marshall
    TI__Genius 10974 points

    >"To help reduce this issue, you need a way to make sure there is a discharge path (such as implementing an external shunt resistor) attached to the unselected inputs so they will not have any built up charge when switched to."

    In my case I have 2.2MOhm resistor between GUITAR IN and Ground, another 2.2MOhm resistor between SITAR IN and Ground and another 2.2MOhm resistor between PEDAL IN and Ground. Shouldn't the 2.2MOhm act as a shunt resistor?

    Regards,
    Luke

    Hi Luke,

    Reopening this thread. The issue with the 2.2MOhm resistor is that it may be too large of a resistor to discharge the node fast enough between transitions. I would advise to use a lower value if you can to better assist in the discharging process.

    Thanks!

    Bryan

  • 0
    Intellectual 340 points

    Hi Bryan, I agree regarding the 2.2MOhm being too large. What range of values would you suggest? Would 100KOhm work perhaps?

  • 0 in reply to Luke Galea
    TI__Genius 10974 points

    Hi Luke,

    So it depends on how quickly you are switching between your inputs. The faster you are switching, the more quickly you need to discharge that node. You could need 50 ohms or 100kOhms could be good enough, that is something you might need to do some trial and error to see what value would work in your application.

    Thanks!

    Bryan