Isolating Capacitance between Filters

[DylanBenton]

Hi Everyone,

not sure if this is a really simple question I'm struggling with, but i was wondering how you isolate capacitance? I have a LPF next to a HPF at the start of a TL071 Buffer circuit, but the cap to ground of the LPF is in parallel to the ones in the HPF. Is there an easy way to stop interactivity between the two by isolating those capacitors?

Im trying to have them as switchable filters, but im struggling to implement it properly.

[PRR]

Welcome.

....the cap to ground of the LPF is in parallel to the ones in the HPF.

So?

And it is not really "in parallel". The HPF caps have another 1Meg in series.

[PRR]

Simming shows both networks doing about what you expect for either one alone. There is an interaction, but for well-spaced frequencies and very well spaced impedances it is part-dB.

[zesak]

If you are concerned that your HPF is loading down the LPF or for some other reason,
you can always put in another TLO buffer between those two sections.
And if you are concerned that your LPF may be loading down whatever is driving it or for some other reason, put a buffer in front of LPF too.
You will end up with three TLO buffers but you get that better cap "isolation".

[idy]

It looks like the beginning of many circuits. Typical. Adding more buffers will make it bulletproof, but is this a stomp box or a tank?

[DylanBenton]

Thanks everyone.

Turns out I'm an idiot and I hadn't set my multimeter to relative and the leads were adding capacitance which led my mind down a rabbit hole...

Was that simulation done in spice? I need to ready more tutorials on it