Hey synth builders!
I would like to add the following filter to my rack. It sounds amazing <3
However, I would really like to add a high-pass switch to it. I found that this is possible for the MS-20 filter design (see this for example). However, would it be also possible for this design in some way?
Thanks in advance!
G’day there,
Adding a HP mode to a diode ladder filter is something I’m looking into as well.
My understanding is that you can’t do it by simply changing where you connect the input, like you would with an op-amp based filter such as the MS-20 filter you’ve pointed to.
One approach, which I haven’t had much luck simulating, but am trying to breadboard, is to take the LP output of the filter, and subtract it from the original input signal and see if that gets you a HP filter. Care needs to be taken with the phase and polarity of the signals - I’m not sure what it looks like in @moritzklein’s version, but in the EMS/TB-303 style diode ladder filters the LP out is around 180Deg out of phase. Plus, I’m not sure what will happen when you have resonance cranked up…
Sorry, not much concrete help, if I do get anything working I’ll be sure to share. Do let me know how you get on!
Cheers
No HP but a Band pass add , see in this thread 
ooohh <3 love it. I also didn’t have bandpass yet. In that case, I will try and add a low-pass / band-pass switch to the design instead
One approach, which I haven’t had much luck simulating, but am trying to breadboard, is to take the LP output of the filter, and subtract it from the original input signal and see if that gets you a HP filter.
Interesting approach indeed. Might not be easy since you have to get the phase/amplitude completely right, so in all cases, it requires extra fiddling in practice. This is a demonstration of the technique:
next video will be exactly on this topic, should be up in about two weeks!
Thanks for all the videos mate! I love them! Can’t wait to build it!