Would this work as a variable high pass filter?

[theleakydiode]

Would this arrangement work as a variable high pass filter at the input of an audio amp? I've tried LTspice but I can't work out how to work it. Also what variable resistor value should I use for it have give good adjustability?


I assume it would do something but what would the rolloff look like when plotted?

I'm a bit of a noob,
Thanks.

[bob91343]

The way it's set up you have two high pass filters in parallel.  Turning the pot varies the contribution of one filter.  With the pot at max the filter uses one capacitor.  With the pot at zero, the frequency is dropped one octave.  In between I think you will get a combination of the two.  Of course this isn't a sharp filter so the results won't be startling.

Imagine the cutoff characteristic of the filter in each extreme pot setting, and the characteristic would be a curve in between the two.

Just a guess.

[Berni]

Yep as bob said this is two filters in parallel.

You will probably get bit of a step in your cutoff response where you can run that step up and down with the potentiometer.

The better way is to adjust that resistor to ground. This is what will actually shift the cutoff frequency back and forth. The values for that can be calculated using the online RC high pass filter calculators.

Also if you expect the cutoff to be very sharp, this will not do it. Sharp cutoff filters need a different design or multiple stages.

[thequantizer]

Try simulating it and you can see how it will behave. We have a post that includes a video on how to simulate a RC High Pass Filter in KiCad. Just modify the circuit to look like your design and see how it works!

 High Pass Filter Calculator

[magic]

I've tried LTspice but I can't work out how to work it.

Set V1 value to AC 1.
Replace VR1 with a resistor and set its value to {pot}.
Press s and add .step param pot 0 1000 100 or similar.
Set simulation command to AC and choose your frequency range.
Enjoy

[mikerj]

A 10k variable resistor will give a -3dB range of approximately 110-250Hz, assuming negligible source impedance and very high load impedance.  I have attached a simple LTSpice model that you can experiment with.