The OP-HPF High Pass Filter

I wanted to have an Isolator-style high pass filter device to play with.

I found this design at that uses a very common op-amp, the TL072.

And there I found the design for a 555-driven negative voltage generator, needed for the TL072:

The only case I got is that Walkers biscuits box. Well English. I punched two holes to mount a rotary switch and a 50k pot, and added big buttons.

The rotary switch will select between 3 different max-cutoff frequency, which will be controlled by the right pot. I chose 220nF, 150nF, and 66nF. The smaller the cap, the higher the Cf.

Here I soldered the 4 wires of the rotary switch and the 2 wires of the 50k pot.

You can see the breadboard with the TL072 for the filter and the 555 used to get a -12V negative rail.

Got all that stuff inside the box.

Here it is. A very British design indeed.

Quick demo. Plug your PC in a PA.

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