Hi, I am in process of upgrading my DIY Amp based on TPA 3116D2. Right now C11 & C13 are changed to good quality film caps and I am very impressed by the sound quality as it is now. In pursuit of refining it further, I am thinking of changing C12 & C14 as well if it can bring further improvements on the sound quality. Attached is the TPA3116D2 datsheet screenshot as well.
I would be inclined to use exactly the same type of capacitor for all four of them because of what is in the datasheet ( https://www.ti.com/document-viewer/tpa3116d2/datasheet ):
In section 7.2, you see that both inputs go to a fully differential amplifier. If this fully differential amplifier had a stiff input common-mode loop that kept the input common-mode voltage constant, then you could argue that any type of non-microphonic capacitor should do for C12 and C14, but there is no indication that it has such a common-mode loop (and output common-mode loops are far more usual anyway). Without it, C12 and C14 essentially have the same function as C11 and C13; the whole path from the signal source via C11, the positive input resistor, the negative input resistor and C12 determines how the input voltage is converted to a current that drives the amplifier.
This also seems consistent with section 7.3.7 of the datasheet:
"To use the TPA31xxD2 family with a single-ended source, ac ground the negative input through a capacitor equal in value to the input capacitor on positive and apply the audio source to either input. In a single-ended input application, the unused input should be ac grounded at the audio source instead of at the device input for best noise performance. For good transient performance, the impedance seen at each of the two differential inputs should be the same."
In section 7.2, you see that both inputs go to a fully differential amplifier. If this fully differential amplifier had a stiff input common-mode loop that kept the input common-mode voltage constant, then you could argue that any type of non-microphonic capacitor should do for C12 and C14, but there is no indication that it has such a common-mode loop (and output common-mode loops are far more usual anyway). Without it, C12 and C14 essentially have the same function as C11 and C13; the whole path from the signal source via C11, the positive input resistor, the negative input resistor and C12 determines how the input voltage is converted to a current that drives the amplifier.
This also seems consistent with section 7.3.7 of the datasheet:
"To use the TPA31xxD2 family with a single-ended source, ac ground the negative input through a capacitor equal in value to the input capacitor on positive and apply the audio source to either input. In a single-ended input application, the unused input should be ac grounded at the audio source instead of at the device input for best noise performance. For good transient performance, the impedance seen at each of the two differential inputs should be the same."
