This low-pass filter, taken from the Synthesizer Arturia Minibrute is rated at 15 MHz.
$$\frac{1}{2\pi RC} = \frac{1}{2\pi \times 100\Omega \times 100\text{ pF}} = 15,915,494.3092$$
Why would you aim so high?
Wouldn't a 68 nF do the job as well, or would it cost amplitude of a 10 V peak to peak signal?
$$\frac{1}{2\pi RC} = \frac{1}{2\pi \times 100\Omega \times 68\text{ nF}} = 23.4051386719\text{ kHz}$$
There's one thing you missed out: The gain-bandwidth product of the operational amplifier.
Even if you are correct that the input filter has a cutoff frequency of 15.9 MHz in theory (neglecting the output impedance of the audio source), the actual cutoff is dominated by the operational amplifier because of the fact that the GBW of TL062 is 1 MHz.
So it's not possible that this amplifier has a cutoff frequency of higher than 1 MHz.
$$ \mathrm{ GBW = A_v \cdot BW \\ \Rightarrow 1\ 10^6 = (1+\frac{33k}{10k}) \cdot BW \\ \Rightarrow BW = 232.56\ kHz } $$
As you can see, the 100pF at the input filter does nothing for the audio input frequencies. So even if you remove that capacitor, the bandwidth will not change. However, there's a risk of radio frequencies being picked up if the input comes from a very long cable (thus the cable acts as an antenna). The input filter helps these frequencies to be chopped off for the sake of the amplifier's stable operation.
If you have a chance, I suggest you simulate the circuit.
PS: It's not uncommon for the audio equipment to have cutoff frequencies higher than audible frequencies (e.g. 150kHz).
so you suggest to keep the 100pF capacitor? you can keep it. It has nothing on audible frequencies. But, as I stated in my answer, it helps the radio frequencies to be chopped off for the sake of the amplifier's stable operation.
\$\endgroup\$
Commented
Aug 31, 2021 at 10:36
can i place the 100R and 100pF in front of those 100K resistors? Normally that's what you should do. Because, if you place the 100p after summing, the 100p capacitor will interact with those 100k resistors and make the cutoff frequency way lower. PS: The comments section under an answer is not a suitable place for asking related questions. You should have posted a new question and indicate this current question as "related". Anyway, do this way next time.
\$\endgroup\$
Commented
Aug 31, 2021 at 11:58
The impedance of an audio source would not be 0 ohms so the filter frequency would not be 16 MHz.
That's why also 68nF you suggest is a bad idea, if source impedance is 1 kohm, the cutoff frequency would be 2 kHz.
Typically audio inputs of professional devices have an RF blocking capacitor to filter out high frequency signals from getting to the amplifier input and cause problems in the amplifier which can't handle them, or to prevent high frequency signals from leaking out from the device.
